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MEMOIRS AND PROCEEDINGS

MANCHESTER LITERARY & PHILOSOPHICAL SOCIETY.

(MANCHESTER MEMOIRS.)

Volume LV. (1910-11,

MANCUKSTKR :

-,6, GEORGE STRKKT.

1911.

o'■,67^7^(^^

i/

NOTE.

The authors of the several papers contained in this volume are themselves accountable for all the statements and reasonings which they have offered. In these par- ticulars the Society must not be considered as in any way responsible.

CONTENTS.

MEMOIRS.

I. On the Origin of Cometary Bodies and Saturn's Rings. By Henry Wilde, D.Sc, D.C.L., F.R.S. Plates I.— III. pp. I— 20

(Issued separately 1 November nth, igio).

II. Notes on Scattering during Radio-active Recoil. By Walter Makower, M.A., D.Sc, and Sidney Russ,

D.Sc. With 2 7 ext-figs pp. 1—4

{Isstied separately, December i6th, igio).

III. The Development of the Atomic Theory : (2) The Various Accounts of the Origin of Dalton's Theory. By Andrew Norman Meldrum, D.Sc. pp. i — 12

(Issued separately, Dece/nber 17th, iqio),

IV. The Development of the Atomic Theory : (3) Newton's Theory, and its Influence in the Eighteenth Century. By Andrew Norman Meldrum, D.Sc. ... pp. i — 15

{Isstced separately, December 17th, igio).

V. The Development of the Atomic Theory : (4) Dalton's Physical Atomic Theory. By Andrew Norman Meldrum, D.Sc pp. i — 22

(Issued separately, March 7th, igir).

VI. The Development of the Atomic Tlieory : (5) Dalton's Chemical Theory. By Andrew Norman Meldrum, D.Sc. ... ... pp. I- 18

(Issued separately, March 7th, igil).

VII. The Behaviour of Bodies floating in a Free or a Forced Vortex. By Prof. A. H. Gibson, D.Sc. With Text-Jig. ... ... ... ... ... ... pp. I — 19

(Issued icparately, March 7th, igil).

VIII. Studies in the Morphogenesis of certain Pelecypoda : (i) A Preliminary Note on Variation in Unio pictorum, Unio Tiimidtis, and Anodonta cygnea. By Margaret C. . March, B.Sc. Plate mid j Text-Jigs pp. i — 18

(Issued separately, March 14th, igri).

VI CONTENTS. «

IX. On an Abnormal Spike of Ophioglossum vulgatum. By

H. S. IIOLDEN, B.Sc, F.L.S. With 6 Text-figs. pp. i— 13 (Issued separately, March 2ist, i<)ii).

X. The Boric Acids. By Alfred Holt, M.A., D.Sc.

With 2 Text-figs pp. 1—9

{Isszced separately-, April 20th, igii).

XI. Studies in the Morphogenesis of certain Pelecypoda : (2) The Ancestry of Trigonia gibbosa. By Margaret COLLEY March, B.Sc. Plate and 3 Text-figs. ... pp. i — 12 {Issiied separately, A iril 20th, iQii).

XII. Some Physical Properties of Rubber. By Prof, Alfred Schwartz and Philip Kemp, M.Sc.Tech. With 11 Text-figs pp. I — 22

(Issued separately, May 2nd, igii).

XIII. The Manner of Motion of Water Flowing in a Curved

Path. By Prof. A. H. Gibson, D.Sc pp i— S

(Issued separately. May 4th, igii).

XIV. On the Periodic Times of Saturn's Rings. By Henry

Wilde, D.Sc, D.C.L., F.R.S pp. 1—3

(Issued separately. May 8th, igii).

XV. Studies in the Morphogenesis of certain Pelecypoda : (3) The Ornament of Trigonia clavellata and some of its Derivatives. By Margaret Colley March, B.Sc.

With IS Text-figSk pp. i — 13

(Issued separately. May 30th, igii).

XVI. A Plesiosaurian Pectoral Girdle from the Lower Lias. By

D. M. S. Watson, JM.Sc. With 2 Text-figs. ... pp. 1—7

(Issued separately. May igtk, igii).

XVII. The Upper Liassic Reptilia. Part 3. Microdeidiis Macro- pterus (Seeley) and the Limbs of Alicrocleidiis homalo- spondylus (Owen). By D. M. S. Watson, M.Sc. With

3 Text-figs pp. 1—9

(Issued separately. May 2gth, igii).

CONTENTS.

Vll

XVIII. Notes on some British Mesozoic Crocodiles. By D. M. S.

Watson, M.Sc. With 4 Text-figs. pp. i-

{Issued separately, May 2<)th, igii).

XIX. The Development of the Atomic Theory : (6) The Re- ception accorded to the Theory advocated by Dalton. By Andrew Norman Meldrum, D.Sc... ... pp. i-

(Iss7ted separately, May zgtk, iQii).

XX. The Conditions that the Stresses in a Heavy Body should be purely Elastic Stresses. By R. F. Gwyther,

M. A.

{Issued separately. May 22nd, igii).

pp.

I — 12

XXI. Uioptriemeters. By Prof. W. W. Halbane Gee and

A. Adamson. With 8 Text-Jigs pp.

{Issued separately, June ist, igii]-

-16

XXII. The Development of the Atomic Theory : (7) The Rival Claims of William Higgins and John Dalton. By Andrew Norman Meldrum, D.Sc pp. i-

{Issued separately, June 12th, igii).

XXIII. On a Specimen of Osteocella Septeiitrionalis (Gray). By Sydney J. HiCKSON, F.R.S. With 3 Text-figs.... pp. {Issticd separately, Jjtne i6th, igii).

I — 15

XXIV. An Account of some Remarkable Steel Crystals, along with Some Notes on the Cr}'stalline Structure of Steel. By Ernest F. Lange, M.I.Mech.E., etc. 2 Pis. ... pp. i— 15 {Issued separately, August 2/st, igii).

PROCEEDINGS i.— xxviii.

General Meetings i., iv., vii., ix., xi., xxiii., xxvii.

Annual General Meeting ... ... ... ... ... ... xxv.

Report of Council, 191 1, with obituary notices of Prof. Stanislao Cannizzaro, Rev. Robert Harley, Prof. J. H. van't Hoff, and Sir William Huggins, O.M., K.C.B. xxix. — xlii.

Treasurer's Accounts... ... ... ... ... ... ... xliii.^ — xlv.

List of the Council and Members of the Society ... ... ... xlvi. — Ixi.

List of the Awards of the Dalton J\Iedal Ixi.

List of the Wilde Lectures Ixii. — Ixiii.

List of the Presidents of the Society Ixiv. — Ixv.

INDEX.

M = Memoirs. P= Proceedings. Abnormal Spike of Opliioglossnm vitlgatum. By H. S. Holden. IM. 9. Action of hydrogen-peroxide on quinone. By E. Knecht. P. xxiv. Adamson, A. and Gee, W. W. H. Dioptriemeters. M. 21. Alpha and ^ rays, scattering of. By E. Rutherford. P. xviii. Alpha particles, large scattering of. By H. Geiger. P. xx. Ancestry of Trioonia gibbosa. By M. C. Marcli. M. 11. Animal metabolism, influence of atmospheric pressure and humidity on. By

W. Thomson. P. xxii. Anodonta cygnea, variation in. By M. C. March. M. 8. Atmospheric pressure and luimidity, influence on animal metabolism. By

W. Thomson. P. xxii. Atom, structure of. By E. Rutherford P. xviii.

Atomic Theory, development of. By A. N. Meldrum. M. 3, 4, 5, 6, 19, 22» Bealey, Dr. Adam, and Dr. Dalton. iiy F. Nicholson. P. xii. Behaviour of bodies floating in a vortex. By A. H. Gibson. M. 7. Bodies floating in a vortex, behaviour of. By A. H. Gibson. M. 7. Boric Acids. By A. Holt. M. 10. Brain, convolutions of. By G. Elliot Smith. P. v. British Mesozoic crocodiles. By D. M. S. Watson. M. 18. Cannizzaro, Stanislao, obituary notice of. By A. N. M. P. xxxii. Cometary bodies, origin of. By H. Wilde. M. i. Convolutions of the brain. By G. Elliot Smith. P. v. Crocodiles, some British Mesozoic. By D. M. S. Watson. M. 18. Crystalline structure of steel. By E. F. Lange. M. 24. Dalton, J. and A. Bealey. By F. Nicholson. P. xii.

and W. Higgins, rival claims of. By A. N. Meldrum. M. 22.

Dalton's atomic theory, reception of. By A. N. Meldrum. M. 19. Dalton's chemical theory. By A. N. Meldrum. M. 6. Dalton's physical atomic theory. By A. N. Meldrum. M. 5. Dalton's theory, accounts of origin of. By A. N. Meldrum. M. 3. Dawkins, W. Boyd. Origin of Roman numerals i. — x. P. xvi. Development of the Atomic Theory. By A. N. Meldrum. M. 3, 4, 5, 6,.

19, and 22. Dioptriemeters. By W. W. H. Gee and A. Adamson. M. 21. Elastic stresses in a heavy body. By K. F. Gwylher. M. 20. Exhibit of cast of Gibraltar skull. By G. Elliot Smith. P. xviii. Exhibit of Gyi)iiiosporanginin. By F. E. Weiss. P. xxvii. Gee, W. W. H. and Adamson, A. Dioptriemeters. M. 21. Geiger, H. The large scattering of the a particles. P. xx.

INDEX. IX

Gibraltar skull, exhibit of cast of. By G. Elliot Smith. P. xviii. Gibson, A. H. Behaviour of bodies floating in a free or a forced vortex. M. 7.

The manner of motion of water flowing in a curved path. i\I. 13.

Gwyther, R. F. The conditions that the stresses in a heavy body should be

purely elastic stresses. M. 20. Gymnosporangiiu)i, parasitic on the common Juniper. Exhibited by F. E.

Weiss. P. xxvii. Harley, Rev. Robert, obituary notice of. By F. N. P. xxxv. Hickson, S. J. On a specimen of Csteocella septentrionalis (Giay). M. 23. Higgins, W. and J. Dalton, rival claims of. By A. N. Me'drum. M. 22. Hoff, J. H. van't, obituary notice of. By N. S. P. xxxvii.

reference to death of. By F. Jones. P. xvii.

Holden, H. S. On an abnormal spike of Ophioglossutn vulgaltim. M. 9. Holt, A. The boric acids. M. 10.

and Myers, J. E. The hydration of metaphosphoric acid. P. xvii.

Huggins, Sir William, obituary notice of. By H. S. P. xxxix.

Hybrid of Oxlip {Primula elaiior) and Primrose {P. acaidis). Exhibited

by F. E. Weiss. P. xxiv. Hydration of Metaphosphoric acid. By J. E. Myers and A. Holt. P. xvii. Hydrogen peroxide, action of on quinone. By E. Knecht P. xxiv. Influence of atmospheric pressure and humidity on animal metabolism. By

W. Thomson. P. xxii. Jones, F. Reference to death of Prof. J. IT. van't Hoft. P. xvii. Kemp, P. Demonstration of effects of heat on pure rubber strip. P. x.

and Schwartz, A. Some physical properties of rubber. M. 12.

Knecht, E. On the action of hydrogen peroxide on quinone. P. xxiv. Lange, E. F. An account of some remarkable steel crystals, along with

some notes on the crystalline structure of steel. M. 24. I>arge scattering of the a particles. By H. Geiger. P. xx. Lower Lias Plesiosauiian pectoral girdle. By D. M. S. Watson. ]\L 16. Makower, W. and Russ, S. Notes on Scattering during Radio-active

Recoil. M. 2. Manner of motion of water flowing in a curved path. By A. H. Gibson.

M. 13. March, M. C. Studies in the Morphogenesis of certaia Pelecypoda : (i) A

preliminary note on variation in Unio pictortmi, Unio iuinidus, and

Anodonta cygnea. M. 8. (2) The ancestry of Triooiiia gibbosa.

^L II. (3) The ornament of Trigonia davellata and some of its

Derivatives. i\L 15.

X INDEX.

Meldrum, A. N. The Development of the Atomic Theory : (2) the various accounts of the origin of Dalton's theory. M. 3. (3) Newton's theory, and its influence in the iSth century. M. 4. (4) Dalton's physical atomic theory. M. 5. (5) Dalton's chemical theory. M. 6. (6) The reception accorded to the theory advocated by Dalton. M. 19. (7) The rival claims of W. Higgins and J. Dalton. M. 22.

Obituary notice of Stanislao Cannizzaro. P. xxxii.

Metaphosphoric acid, hydration of. By J. E. Myers and A. Holt. P. xvii. Microckidus homalospondyhis (Owen), limbs of. By D. M. S. Watson.

M. 17. Microckidus macropierus (Seeley). By D. M. S. Watson. M. 17. Morphogenesis of certain Pelecypoda. By M. C. March, (i) M. 8. (2)

M. II. (3) M. 15. Myers, J. E. and Holt, A. The hydration of metaphosphoric acid. P.

xvii. Newton's theory, and its influence in xviiith cent. By A. N. Meldrum.

M. 4- Nicholson, F., Dr. Adam Bealey and Dr. Dalton. P. xii.

Obituary notice of Rev. R. Harley. P. xxxv.

Obituary Notices. — Cannizzaro, S. P. xxxii. Harley, Rev. R. P. xxxv.

Hoff, J. H. van't. P. xxxvii. Huggins, Sir W. P. xxxix. Ophiogkssum znc^gafutii, abnormal spike of. By II. S. Holden. M. 9. Origin of cometary bodies and Saturn's rings. By H. Wilde. M. i. Origin of Roman numerals i. — x. By W. Boyd Dawkins. P. xvi. Ornament of Tngonia clavellata and some of its derivatives. By M. C.

March. M. 15. Osteocella sepkntrionalis (Gray). By S. J. Hickson. M. 23. Oxlip and Primrose hybrid. Exhibited by F. E. Weiss. P. xxiv. Pavonazzo marble, exhibit of. By G. P. Varley. P. x. Pelecypoda, morphogenesis of. By M. C. March. M. 8, 11, and 15. Periodic times of Saturn's rings. By II. Wilde. M. 14. Physical properties of rubber. By A. Schwartz and P. Kemp. M. 12. Plesiosaurian pectoral girdle from the Lower Lias. By D. M. S. Watson.

M. 16. Prevention of tarnishing of silver-on-glass parabolic mirrors. By T. Thorp.

P. iii. Primrose and Oxlip hybrid. Exhibited by F. E. Weiss. P. xxiv, Priimda elatior and P. acaulis, hybrid of. Exhibited by F. E. Weiss. P.

xxiv. Quinone, action of hydrogen peroxide on. By E. Knecht. P. xxiv. Radio-active Recoil, scattering during. By W. Makower and S. Russ. M. 2.

INDEX. XI

Reception of Dalton's atomic theory. By A. N. Meldruni. M. 19.

Remarkable steel crystals. By E. F. Lange. M. 24.

Roman numerals i. — x., origin of. By W. Boyd Dawkins. P. .xvi.

Rubber, physical properties of. By A. Schwartz and P. Kemp. M. 12.

Rubl)er strip, effects of heat on. By P. Kemp. P. x.

Russ, S. and Makower, W. Notes on Scattering during Radio-active

Recoil. M. 2. Rutherford, E. The scattering of the a and p rays and the structure of the

atom. P. xviii. Saturn's rings, origin of. By H. Wilde. M. i. Saturn's rings, periodic times of. By H. Wilde. M. 14. Scattering during Radio-active Recoil. By W. Makower and S. Russ. M. 2. Scattering of the « and (3 rays and the structure of the atom. Bv E.

Rutherford. P. xviii. Schwartz, A. and Kemp, P. Some physical properties of rubber. M. 12. Sigillai-ia and Sfigmarropsis. By F. E. Weiss. P. x. Silver-on -glass parabolir mirrors, prevention of tarnishing of. By T. Thorp.

P. iii. Smith, G. Elliot. Convolutions of the Brain. P. v.

Exhibit of cast of Gibraltar skull. P. xviii.

Smith, Norman. Obituary notice of J. II. van't Hoff. P. xxxvii.

Stansfield, M. Obituary notice of Sir W. Iluggins. P. xxxix.

.Steel, crystalline structure of. By E. F. Lnnge. M. 24.

Steel crystals, account of some remarkal^le. By E. F. Lange. .M. 24.

Sfigiirarinpsis and Sigillayia, By F. E, Weiss. P. x.

Stresses in a heavy body. By R. F. Gwyther. M. 20.

.Stromeyer, C. E. Process for reproducing sulphide segregations in steel on

photographic paper. P. iii. Structure of the atom. By E. Rutherford. P. xviii. Studies in the Morphogenesis of certain Pelecypoda. By M. C. March.

(I) M. 8. (2) M. II. (3) M. 15. Sulphide segregations in steel reproduced photographically. By C. E.

Stromeyer. P. iii. Thomson, W. On the influence of atmospheric pressure and humidity on

animal metabolism. P. xxii. Thorp, T. Prevention of tarnishing of silver-on-glass parabolic mirrors.

P. iii. Trigonia clavdlata and some of its derivatives, ornament of. By M. C.

March. M. 15. Trigonia gibbosa. ancestry of. By M. C. March. M, 11. Unio pictorum . variation in. By M. C. March. M. 8. Unio titjuidiis, variation in. By M. C. March. M. 8. [ov^r

Xii INDEX.

Upper Liassic Keptilia. Part 3. By D. M. S. Watson. M. 18. Variation in Uniopictoniw, U. ivmidiis. and Anodojjia Cygnta. By M. C.

March. M. 8. Various accounts of the origin of Dalton's theory. By A. N. Meldruni.

M. 3- Varley. G. P. Exhibit of specimen of Pavonazzo marble. P. x. Vortex, behaviour of bodies floating in. By A. II. Gibson. M. 7. W.ater flowing in a curved path, manner of motion of. By A. II. Gibson.

M. 13. Watson, D. M. S. Notes on some British Mesozoic Crocodiles. M. 18.

Plesiosaurian pectoral girdle from the Lower Lias. M. 16.

Upper Liassic Replilia. Part 3. Microcleidiis maitoptenis (.Seeley)

and the limbs of Microcleidiis homalospoiidylus (Owen). M. 17. Weiss, F. E. Exhibit of fungus Gyinnosporangiufn parasitic on the common

Juniper. P. xxvii. Exhibit of hybrid of Oxlip (Primula dalior) and Primrose (/'. acii/is\.

v. xxiv.

On Sigillaria and Stigiiiariopsis. P. x.

Wilde, H. On the origin of cometary bodies and .Saiuins rings. .\L i. On the periodic limes of Saturn's rings. M. 14.

Manchester Memoirs, Vol. Iv. (1910), No. \.

I. On the Origin of Cometary Bodies and Saturn's Rings.

By Henry Wilde, D.Sc, D.C.L., F.R.S.

Received and read Ociobcr 4th, igio.

As the first Halley Lecture which 1 delivered before the University of Oxford in May last* contained some matters new to astronomical science, it has appeared to me that an abridgment of the lecture, with some additions which have since presented themselves to me, would be of value in continuation of my papers recently published by the Society.f

While the principle of dualism is abundantly manifest in every department of knowledge and fully recognized in the attractions and repulsions in molecular physics, the phenomena of the repulsive energy of celestial bodies have so far been unduly obscured by the more general principles of moving force and the attraction of gravitation.

The doctrine that the solar system, as at present constituted, was formed by the successive condensations of a nebular substance rotating about a central position, has been more firmly established during recent years through the great advances made in stellar photography, by which many of the nebula; are visualized in various stages of evolution as right- and left-handed spirals, and clearly indicating the direction of their revolutions.;!:

* Clarendon Press. Frowclc. 19 1 o.

t Manchester Memoirs, vols. 53, 54, 1909, 1910.

Phil. Mag. (6), vols. 18, 19, 1909, 1910. X "Celestial Photographs," by Isaac Roberts, F.R.S. Vols, i, 2, 1893. 1899.

November iit/i, igio.

2 Wilde, Origin of Conietary Bodies and Saturn's Rings.

The more interesting of these nebulse are, M.31 Andromedse, M.51 Canum, M.ioo Comae, M 74 Piscium, and many others from which the origin of planetary systems may be inferred with the same degree of pro- bability as in the historical sequences observable in chemistry, geology, biology, or in any other department of the natural sciences.

That the subsequent condensations of planetary nebulae into spherical bodies would be attended by the evolution of an amount of heat sufficient to make them vividly incandescent, is an obvious conclusion drawn directly from experimental science. It will be further evident that, after the heat of compression had attained its maximum, the self-luminous planets would ultimately become dark bodies through the radiation of their heat into free space.

It is very generally admitted that the sun, notwith- standing his vast dimensions, would, by continuous loss of heat, ultimately become a dark body like each member of the planetary system. It is also known that the internal parts of the sun are in a gaseous condition and under immense pressure. Some idea of the repulsive force exercised by this pressure may be formed from the ejection of enormous masses of incandescent gas from the surface of the sun to the height of 200,000 miles, with an estimated velocity of 166 miles per second.*

Assuming the secular cooling of the sun to be continu- ous, the liquefaction and final solidification of his outward parts would follow in natural sequence in accordance with common experience of cooling bodies, while the central parts would remain in their primitive gaseous condition. From strict analogy, it may justly be inferred that all the planetary bodies have gone through the same stages of

* Young, American Journal of Science, 1 871, p. 468.

Manchester Memoirs, Vol. Iv. (1910), No. |. 3

cooling as those outlined in the instance of the central body.

The notion that the earth and, inferentially, the other planets are solid bodies throughout, finds no support from a reasonable consideration of the constituents of the earth's crust, so far as they are accessible to observation. The late distinguished Professor of Geology in Oxford University (Sir Joseph Prestwich), in his classical work on Chemical, Physical, and Stratigraphical Geology, has clearly demonstrated from the uplift of continental areas and mountain chains, the welling out of basaltic lavas over many thousand square miles of surface and of great thickness, that a comparatively thin crust enveloping a fluid interior is a necessary condition to satisfy the requirements of geologists and physicists. More signifi- cant still is the succession of foldings of the earth's crust and stratigraphic contortions of small curvature, both of which features indicate a thickness of solid crust less than twenty-five miles. How far the imprisoned gases at the centre of the earth and the aqueous vapours near the surface may have contributed respectively to produce these geological changes, it is unnecessary now to discuss, but in the instance of the moon, which has neither water nor an atmosphere, the evidence of intense volcanic action manifested on its surface can only be accounted for by the ejective force of the gaseous substances in its interior, similar to that by which the incandescent gases from the surface of the sun are projected.

The fine series of photographic enlargements of the moon executed by MM. Loev/y and Puiseux, of the Paris Observatory, show the greater part of its surface, from the equator to the poles, covered with extinct volcanoes in every stage of formation, similar to those on the terrestrial elobe. Some of these volcanoes are twelve

4 Wilde, Origin of Cometary Bodies and Saturn's Rings.

thousand feet in height, with their craters upwards of forty miles in diameter, and are striking evidence of the immense repulsive force which produced them.

It has for a long time been considered on good evidence that the planetoids between the orbits of Mars and Jupiter (now numbering more than 600) are the fragments of a large planet which had formerly revolved in an orbit about the same distance from the sun as Ceres, and had been shattered by some internal convulsion. This hypothesis was put forward by Olbers the discoverer of Pallas in 1802, and was made the subject of a memoir by Lagrange in which he determined the explosive force necessary to detach a fragment of a planet that would cause it to describe the orbit of a comet. The nebulosities of the dense atmospheres of some of these planetoids concealing their disks indicate an incipient change of planetary into cometary bodies.

Attempts have been made during recent years to discredit the explanation offered by Olbers of the origin of the planetoids, by assuming that the annulus or convolute of nebular substance failed to resolve itself into a sphere, but was broken up into a number of small bodies.

There is no inherent improbability in the idea of a nebular convolution resolving itself into a number of discrete spherical bodies as many of such are to be seen in the convolutions of spiral nebulae, of which M.ioo Com;c and M.74 Piscium are the most striking examples. The convolutions of these nebulae contain nebular stars which are involved symmetrically and follow the curvature of the convolutions. M.ioo Comae is further interesting from the fact of its showing elongated fissions of the convolutions previous to their development into spherical bodies. Such discrete bodies, revolving in a circular orbit of the same diameter would, by their mutual

Manchester Memoirs y Vol. Iv. (19 lo), No. 1. 5

attractions, ultimately coalesce to form a single planet, as postulated in my paper in connexion with the contraction of the radius vector of Neptune.*

As the orbits of all the planets are nearly in the plane of the ecliptic, and also of comparatively small eccentricity, it would become necessary to further assume that all the rings of discrete bodies should revolve in the same plane of the ecliptic, and in orbits nearly circular as do the other planetary bodies ; but Olbers found that Pallas had the large orbital inclination of 34°7, and many others are inclined from 26 to 15 degrees.

The eccentricities of some of the planetoids are also very large, that of yEthra being 0380, Juno 0'257, and Pallas 0"238. The periodic times vary between 7"86 years (Hilda) and 175 years (Eros) with the correlated large differences in their mean distances from the sun; Hilda being 3'95 astronomical units, and Eros only v\6 units which thereby intersects the orbit of Mars, 1*52 units.

The large differences observable in the elements of the planetoids, clearly indicate them as fragments of a large planet, in accordance with the conclusions arrived at by Olbers in 1802. The illustrious astronomer further assumed that the orbits of all the fragments would inter- sect each other at the point where the explosion occurred. Subsequent observations have, however, shown (which I shall confirm further on) that this supposition, while applicable in many instances, does not hold good as a generalization.

It will now be evident, without further discussion, that had the exploded major planet been a solid body throughout as hard as steel, it would still be revolving in

* Afanchester Memoirs, vol. 54, 1910. Phil. Mag., (6) vol. 19, 1910, p. 604.

6 Wilde, Origin of Couietary Bodies and Satuni's Rings.

its orbit, and would thus have deprived the world of an interesting chapter of astronomical science.

A review of the history of cometary astronomy brings out the remarkable fact that, while much has been written on the nature and motions of comets, few, if any, serious attempts have been made to account for their origin. The general opinion of modern astronomers, in accordance with the views of Kant* and Laplace,f is that these bodies are strangers to the solar system, which have been captured in the course of their lawless wanderings from the depths of the stellar universe

The principal objection to this supposition is the immense distance of the solar system from the fixed stars. The best determination of the distance of the nearest of them was made by Dr. Gill at the Cape of Good Hope in 1881, which showed that a Centauri had a parallax of 075", indicating a distance of about 25 billion miles, or 9,000 million miles more distant from Neptune than that planet is from the sun. As the attraction of gravitation at the orbit of Neptune is only one forty- second millionth of that at the solar surface, the attractive force at the distance of the fixed stars may be considered a negligible quantity in determining the motions of cometary bodies having their origin in other planetary systems. Granting for the moment that comets actually belong to other stellar systems, the problem of their origin and formation would still present itself for solution to earnest inquirers into the nature and causes of things.

The discoveries in cometary astronomy, more espe- cially those of Schiaparelli, that the orbits of certain comets are identical with those of well-known streams of

■ Kant's " Natural History and Theory of the Heavens," Chap'er 3. t Laplace's " Systeme du Monde," 1824.

Manchester Memoirs, Vol, Iv. (1910), No. \. 7

meteors, as instanced in the comets of Tempel and of Biela in relation to the November meteors, clearly point to the conclusion that the place of origin of these erratic bodies is within the confines of the solar system, and that they have, consequently, always been members of it. Moreover, all meteoric bodies, as is well known, are mechanical mixtures of elementary substances or their compounds, and further indicate them as the ejectamenta of planetary bodies.

That comets are planetary ejectamenta, principally from the larger planets, may be justly inferred from the prodigious force manifested by the ejections from other celestial bodies to which attention has already been directed.

The determining cause of the ejection of a comet from any planet would be found in the conjunctive attractions of one or more of their number acting upon that part of the surface from which the cometary matter was ejected. The orbital direction of a comet would be determined solely by the position of the breach in the crust in relation to the orbital motion at the moment of discharge. The motion would be direct when its discharge coincided with the orbital motion of the planet, and retrograde when it was in the opposite direction, as shown in the annexed plate. And, according as the discharge was more or less at right angles to the plane of the planetary orbit, so would the angular direction of the comet in relation to the ecliptic be determined. The discharge of cometary bodies from vents in high planetary latitudes would necessarily have the greatest inclination to the ecliptic. It may be observed in this connexion that some of the large craters on the moon's surface, and of the terrestrial active volcanoes, Hecla and Mount Erebus, are also in high latitudes.

8 Wilde, Origin of Covietmy Bodies and Saturn's Rii/gs.

To those who are not familiar with the problems of experimental mechanics, it may be of some advantage to demonstrate more fully the direct and retrograde motions of cometary bodies by further illustrations than those shown in my Halley lecture.

It is common knowledge, based on well-established observations, that the axial and orbital rotations of all the planets are in the same direction, the sun also revolving on its axis in the same direction as the planets.

As a consequence of the common direction of the axial rotations, the adjoining circumferential parts revolve in opposite directions to each other, as will be seen in the annexed diagram of the Sun and Jupiter. Hence, while the circumferential parts of the planets next to the sun revolve from west to east, the sun apparently revolves from east to west, as is manifest from the motion of the dark spots across the solar disk.

That the circumferences of moving circles rotate about their centres in contrary directions at opposite extremities of their diameters is an axiomatic truth which finds its concrete expression in the diagram referred to. This geometrical relation is also practically illustrated in the reaction steam engine of Hero of Alexandria, in which a hollow globe is made to revolve by two jets of steam issuing in contrary directions from opposite extremities of its diameter. Other instances of direct and retrograde motion may also be seen in the Catharine wheels of ordinary firework displays, and in hydraulic turbines with multiple jets around their circumferences.

Halley's original conception of concentric spheres rotating within the earth, with a differential motion, is fruitful in leading to the further idea that the ejection of comets from a planet may be periodic from causes within

Mane lie ster Memoirs, Vol. Iv. (1910), No. \. 9

itself, in like manner to the eleven years maximum sun-spot ejections of elementary gaseous substances. For it is only necessary to assume that, after the ejection of cometary matter through the double thickness of two concentric shells, the differential motion would retard, or wholly prevent, the further discharge until the vents were again coincident.

The planet Jupiter, from his vast dimensions, is the most interesting member of the solar system for the study of planetary and cometary evolution. The great red spot on his surface is generally considered to be caused by luminous vapours at great depths within the globe, if not by the actual incandescent crust of that part of the planet. The great extent and permanency of this spot indicate it as the locus of one of the vents through which comets and cometary satellites have been ejected at different periods of the history of the planet.

It is now generally recognized that certain groups of periodic comets are associated in some way unknown with the larger planets respectively ; the comets of short period belonging to Jupiter, as nearest to the sun, and the long period comets (of which Halley's is the most notable member) to Neptune and intermediate planets.

All the motions of periodic comets are well explained on the assumption of their moving in elliptical orbits more or less elongated, but the vast tabulated periodic times of comets supposed to move in parabolic and hyperbolic curves are necessarily ultra-speculative.

As the attraction of solar gravitation extends far beyond the orbit of Neptune, the motion of a body on the line of an open curve would ultimately be arrested and a comet would necessarily return over the same track, approximately, with a retrograde motion as an unknown

lO Wilde, Origin of Cometary Bodies and Saturn's Rings.

member of the solar system. Halley's comet, however, is considered to move in an elh'ptical orbit and has, there- fore, the longest periodic time of which astronomers have certain knowledge.

As the principle of conservation holds good alike for celestial and terrestrial bodies, the moving force of comets will not exceed the attraction of gravitation beyond the limits of the solar system, and will be much less through the conversion of molar into molecular motion by friction of the discrete particles of cometary matter among them- selves during the act of ejection, as also from the resistance of the medium through which they move in their orbits, and especially near the sun.

The principle of conservation, as will be obvious, will hold equally for the comets ejected from the planets of other stellar systems. Hence the absurdity of bringing cometary bodies into the solar system which contains within itself the power of evolving its own comets. Moreover, it will be further evident that this immigration notion might be extended to include the Earth and other planets as bodies from other stellar systems, captured by the Sun in their wanderings from outer space.

Jupiter, with his system of satellites, is generally regarded as a miniature solar system formed by the successive condensations of a nebular substance surround- ing the planet. The laws of attraction, moving force, and Kepler's laws have the same relations among his satellites as in the planetary system. The binary progression of the periodic times of the three adjoining major satellites, lo, Europa, and Ganymede (which are very nearly in the ratio of I, 2, 4) indicates an orderly process of evolution similar to that of the binary progression of the planetary distances.

Manchester Memoirs, Vol. Iv. (1910), No. I. 11

The erratic movements and irregular orbits of the three outer Jovian satellites recently discovered have, however, presented a new problem for solution in con- nexion with the nebular theory of the evolution of satellites, as it was found that the orbital motion of the outermost one was in a retrograde direction.

An attempt has been made to explain the anomaly by assuming that Jupiter at an earlier period of his history performed a semi-revolution about his polar axis, and that all the inner satellites turned over, in like manner, in opposition to the orbital direction of their erratic outer member.

An insuperable objection to this ingenious hypothesis is the absence of any causal connexion between the assumed inversions of the axial motions of planets, together with their satellites, and their orbital revolutions, and, consequently, leaves untouched the problem of the retrograde orbital motion of a satellite, which it is the precise object of the hypothesis to explain. The fallacy involved in the scheme will at once be apparent when applied to the orbital rotationsof all the planets which are clearly independent of the positions of their axes of rotation in relation to the plane of the ecliptic. And here it may be useful to apply Newton's ' First rule of reasoning in philosophy,' as laid down in the " Principia " that, ' we are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances ; for Nature does nothing in vain, and more is in vain when less will serve, for Nature is pleased with simplicity, and affects not the pomp of superfluous causes.'

I have already said that when a comet is ejected from a planet opposite to the orbital motion its direction would

12 Wilde, Origin of Covietarv Bodies and Saturn's Rings.

be retrograde to that of the planet from which it was ejected.

The orbital velocity of Jupiter being eight miles per second, a body ejected from its interior at a much greater velocity (which I will call the critical velocity) would, by the diminished attraction of the planet, conjointly with the action of solar gravity, revolve with a retrograde motion in an irregular and much enlarged orbit in accordance with the observations {Plate i). And if ejected with a velocity much greater than that necessary to retain it within the sphere of the planet's attraction, the body would move in a separate and elliptical orbit as a comet.

Considering the comparative minuteness of Jupiter's three outer satellites, which are estimated to be less than thirty miles in diameter, and that the orbits of J VI and J VI I are both inclined at 30" to the plane of the ecliptic, and have nearly the same periodic times and distances, these small bodies are hardly entitled to rank as satellites, but may rightly be regarded as planetary ejectamenta. Nevertheless, the discovery of them is of great importance, as furnishing another indirect proof of the planetary origin of comets.

Applying the foregoing principles of direct and retro- grade motion of cometary bodies to the explosion of a whole planet between Mars and Jupiter, the fragments projected opposite to the orbital motion would be retarded, and by the action of solar gravity revolve in a smaller orbit than that of the planet before the explosion. On the other hand, the motion of the fragments coincident with the orbital direction would be increased, and by the diminished action of the sun's attraction, revolve in a larger orbit in accordance with the observations. In neither of these cases, however, would the orbits of the

Manchester Memoirs, Vol. Iv. (1910), No. 1. 13

fragmentary bodies again intersect each other at the point of the planet's orbit where the explosion occurred.

All the observations which I have made on the evolution of the Jovian satellites and cometary ejecta, are applicable alike to the Saturnian and other systems of planetary satellites. The evidence of orderly progression in the periodic times of the inner satellites of Saturn differs in one respect from that indicated by the satellites of Jupiter in similar positions, as the times of revolution of the first and third satellites are in the ratio of i and 2, and the times of the second and fourth are also in the same ratio, as was first pointed out by Sir John Herschel.*

Notwithstanding that the actual surface of Jupiter is covered with dense vapours of great depth, just as the terrestrial globe at one period of its history was enveloped with an atmosphere of aqueous vapour which has since condensed to form the oceans, several facts, in addition to those advanced indicate that the Jovian planet has a solid crust of considerable thickness.

The remarkably bright round spots which suddenly appear on the planet at irregular intervals, and have been described by Lassell, and also by Dawes, as having some resemblance to lunar craters,j- indicate considerable vol- canic activity below the atmospheric envelope. The eruptive matter from the Jovian craters also produces the appearance of belts on his outer surface as well as those seen on Saturn and Uranus. That these belts and bands are caused by volcanic dust ejected to great heights from the interior parts of planetary bodies is highly probable from observations made on the great eruption of Krakatoa in 1883.+

* " Outlines of Astronomy," p. 368, 1864.

t Monthly Notices Roy. Ast. Soc, vol. 10, 1850; Ibid., vol. 18, 1857. X " The Eruption of Krakatoa and Subsequent Phenomena." Report of the Krakatoa Committee of the Royal Society, 1888.

14 Wilde, Origin of Cometary Bodies and Saturn s Rings.

The ejecta from this volcano reached a height of more than 30 miles, forming a belt 20° wide on each side of the equator, and made two successive revolutions round the globe in the course of twenty-five days. The optical phenomena attending the eruption also included blue, green, and copper-coloured suns similar to the transient colours observed on the belts of Jupiter.

The problem of the origin of Saturn's rings has for a long time engaged the attention of natural philosophers, but no solution has yet been offered of sufficient im- portance to gain the general assent of astronomers. The first of these attempts was made in 1755 by Kant in his " Natural History and Theory of the Heavens," wherein he assumes that Saturn at an early period of its history had the characteristics of a comet and moved in an orbit of great eccentricity. That its tails gradually contracted upon the planet to form a cometic atmosphere of vapours which subsequently changed into the form of a ring entirely separated from the body of the planet.

In the " Systeme du Monde " of Laplace the rings are supposed to be the original nebular substance uncon- densed into the form of satellites. This opinion has since been strongly held by astronomers and other scientific investigators and utilised as an illustration of the nebular theory of the origin of planetary systems.

Recent spectroscopic and mathematical investigations have, however, shown that the rings consist of a vast number of minute bodies, in confirmation of the views previously advanced by J. D. and J. Cassini in the Memoirs of the F rend I Academy of Sciences in 1705 and 1715.

In neither of the explanations of the origin of Saturn's rings by Kant and Laplace is there any suggestion of the

Manchester Memoirs, Vol. Iv. (1910), No. I. 15

interior of the planet as being the birthplace of these singular appendages. It is therefore with some amount of diffidence that 1 venture to affirm that they are the ejectamenta of Saturn when its diminishing energies were insufficient to eject a cometary satellite, or a comet with its train of meteorites beyond the sphere of its gravita- tional attraction. And here it may be well to remark that all meteoric and other small discrete bodies are not formed directly from the universal nebular substance, but are necessarily fragments of the solid or liquid parts of a globe, which had a long previous history, involving the evolution of the several series of elementary substances of which the globular body was composed.

The dimensions of Saturn's rings are drawn up in the following table for a new determination of the times of their revolutions, and are based upon the commonly accepted equatorial diameter of the planet = 73.860 miles or the semi-diameter of 36,930 miles.

The dimensions have been calculated from scaled measurements which I have made of reproductions of the fine photographs of Saturn taken at the Lick* and other Observatories during recent years, and which surpass in accuracy those calculated from observations and micro- metric measurements.

The radial dimensions of the rings on the line of the equatorial diameter of the planet have the same propor- tional relations at different angles about this diameter, and constitute the basis of the method of measurements which I have adopted.

In accordance with the notation of O. Struve, now generally adopted, I have designated the rings A, B, and C, in the order of their distances from the planet.

* Todd, "Stars and Telescopes," 1900.

1 6 Wilde, Origin of Conic tary Bodies and Satunis Rings.

ELEMENTS OF SATURN'S RINGS.

Distance from centre of Saturn.

Time of Revolution.

Rings.

Sat. Units.

Miles.

h. m.

Exterior A.

2-30

84,937

12 48

Breadth

026

9,602

„

Mid-breadth ...

2-17

80,138

II 45

Interior A.

2-04

75,337

10 42

Interval

007

2,585

,.

Exterior B. ...

1-97

72,752

10 9

Breadth

0-47

17,357

,, ,,

Mid-breadth ...

1735

64,073

8 24

Interior B.

1-50

55,395

6 44

Exterior C.

1-50

55,395

6 44

Breadth

023

8,493

,, ,1

Mid-breadth ...

1-385

51,148

6 00

Interior C.

1-27

46,901

5 15

liall Space

027

9,971

,. „

Sat. Ball

TOO

36,930

10 13

Mimas

336

1 24,084

22 37

Manchester Mejnoirs, Vol. h. (1910), No. \. 17

The velocity with which a body is ejected from the interior of a planet, as I have said, determines whether it shall be designated a comet, a cometary satellite, or a cometary ring. If the latter, it will be obvious that, from whatever part of the circumference of the planet the discharge takes place, the ejected matter will necessarily move in the same direction as the axial rotation. More- over, if the discharge continued without interruption during one or more rotations of the planet a complete ring of discrete bodies would be formed in accordance with the accepted theory and observations.

It will be further evident from the three orders of cometary discharge specified above, the formation of the outer ring A preceded that of the next inner ring B, as shown by the interval of 2,585 miles of clear space between them.

That the second ring was formed some time sub- sequently to the first, is highly probable from the long period of intermittent discharges observable in terrestrial volcanoes, and also in celestial explosive action, of which there are abundant instances in planetary volcanoes and variable stars.

That the third and dusky ring C of Saturn represents its last and final effort of cometary evolution is shown by the wide separation of the discrete bodies of which the ring C is composed, and further indicated by its semi- transparency through which the body of the planet is distinctly visible.

I have not included in the table of distances the now well-recognized subdivisions of the exterior ring A and of the dusky ring C, so distinctly seen in the photographs, but they are sufficiently definite for a measurement to be taken of their width, which is approximately 230 miles.

1 8 Wilde, Origin of Conietary Bodies and Satunis Rings.

The thickness of the rings is difficult to determine on account of the great distance of Saturn from the earth, and has been estimated by Herschel as not exceeding 250 miles. Assuming this value to be approximately correct, the vent in the crust of the planet through which the matter of the rings was ejected may not have been larger than those from which it is assumed the outer satellites of Saturn and Jupiter were also ejected.

The polar compression of Saturn is well determined by the photographic method when the edge of the ring alone is visible, and is in the ratio of 10 to 1 1 of the equa- torial diameter. The value of the compression from good

observations varies between and

9"02 1 01 9

Turning now to the times of revolution of Saturn's rings respecting which there are wide differences of opinion, arising from the fact that there are no distinctive marks on their surfaces from which their rotations can be determined.

Laplace and also Herschel were content to consider the rings as one body, and both assigned the period of its rotation to be 10 hours 32 minutes, as being the time of a satellite revolving at the same distance as the middle of its breadth.

Later investigators have, however, found it necessary to recognize, from the discrete constitution of the rings, the different times of revolution of their outer and inner circumferences, but have still treated them as one body, and assigned a period of 12 hours 5 minutes for the outer circumference, and 5 hours 50 minutes for the inner edge of the dusky ring C.

From the fact that the ring A is separated from the inner ring B by a clear space of 2,585 miles, the time of

Manchester Memoirs, Vol. Iv. (1910), No. 1. 19

its revolution may be determined independently of the times of B and C.

As the ring A is postulated to be the first annular ejection from the planet, its outer edge would be the extreme limit of the ejective force, and it would conse- quently revolve in the same time as a satellite at the same distance, in accordance with Kepler's third law. Now the period of Mimas, the first satellite of Saturn, is 22 hours 37 minutes, hence we have for the outer edge of the ring a periodic time of 12 hours 48 minutes ; and ii hours 45 minutes as the time of rotation at the middle of its breadth.

Dealing with the second ring B in the same manner, we have for the outer edge a period of 10 hours 9 minutes, and for the middle breadth, 8 hours 24 minutes as the period of revolution.

The determination of the time of revolution of the dusky crape ring C presents some difficulty on account of the wide separation of the discrete particles of which it is composed, and its apparently close contact with the interior of the ring B, but as by Kepler's law the time of revolution of the interior of B would be 6 hours 44 minutes, the exterior parts of C may be assumed to revolve at the same rate, and the inner edge of C in 5 hours 15 minutes.

From the principle of the transformation of energy it may be rightly inferred that some of the molar motion of the vast assemblage of discrete particles constituting the rings would be converted into heat, with a consequent slow •contraction of their orbits. The observations collected by O. Struve in favour of such contraction have been discussed by astronomers, but without so far arriving at any definite conclusion.

20 Wilde, Origin of Covietary Bodies and Saturn's Rings,

The resemblance of Saturn's rings to the Zodiacal Light is briefly indicated by Kant in a short chapter of his ' Theory of the Heavens,' in which he accounts for its origin by assuming that the fire of the sun raises from its surface vapours similar to those which formed Saturn's ring, and by their motion around the sun formed an .expanded plain in the plane of the sun's equator, or in the figure of a convex lens.

Modern investigators have since carefully observed this singularly interesting object, and mostly agree that it is a vast accretion of cometary and meteoric particles from outer space and extending beyond the earth's orbit, but none of them, so far as I know, has suggested the interior of the sun as the place from which the Zodiacal substance has been ejected.

That cometary and meteoric matter may have contri- buted to the volume of discrete bodies surrounding the sun and extending to some distance within the orbit of Mercury has some degree of probability in its favour, but the extreme tenuity of the outermost parts of the Zodiacal substance, together with its immense distance from the central body, appears to me to be better accounted for on the supposition of its consisting of the lighter elementary substances in a state of extreme sub-division ejected during solar eruptions, as in the instance of the ejection of enormous masses of hydrogen observed by Young which I have already adduced.

CORRIGENDUM and ADDENDUM.

Page 6 line 18,/^?;- " 9000 million miles " read " 9000 times." onnn v r>. 7S^ I'^n /tnn = ic; c\\ i r\if\ f>r\n c\r\f\ nnilf>Q

Manchester Memoirs, Vol. L V. {No. 1),

Plate I.

CoMETARY Satellites with Retrograde Motion.

Manchester Memoirs, Vol. L V. {No. 1).

Plate II.

Scaled Diagram of Saturn's Rings.

Manchester Memoirs, Vol. L V. {No. 1). Plate III.

Manchester Memoirs, Vol. Iv. (1910), No ?J.

II. Note on Scattering during- Radio-active Recoil.

By Walter Makower, M.A., D.Sc,

AND

Sidney Russ, D.Sc.

Received and read November ijtii, igio.

In the course of some experiments on the recoil of radium B from radium A, it was found that not only did a surface directly exposed to the recoil stream become active, but surfaces situated outside the direct stream also received active deposit. It was thought that these effects were due to reflection or scatterinij from the surfaces

Fig. I.

upon which the recoil-atoms fell, and a few preliminary experiments were made to test this hypothesis. The experiments, which were carried out in a high vacuum, were made in the following way. A plate S was mounted as shown in Figure i in such a way that it was outside

December j6t/i, igio.

2 Makowek, Scattermg during Radio-active Recoil.

the recoil-stream coming from the active wire P, coated with radium A, but so that recoil-atoms reflected or scattered from the copper reflector O could reach it. The distance from the wire to the reflector O was 1*4 cms., and that from the reflector to the surface V2 cms. After an exposure of ten minutes in vacuo, the plate S was removed and found to be active, and the nature of the

\^

Fig. 2.

active matter on the plate was ascertained by measuring its rate of decay with an a-ray electroscope. After expos- ing a plate for ten minutes to the radium B expelled from the wire, the activity should at first rise and attain a maximum after 27 minutes, and then fall ofl" with time aS indicated by the dotted curve {Figure 2), which has been

Manchester Memoirs, Vol. Iv. (1910), No. %. 3

calculated theoretically. It will be seen that curve B, which represents the results of the experiment just described, hardly rises at all, remaining nearly constant at first, and beginning to decay after about 20 minutes. The curve indicates that more than half of the active matter reaching S was radium C, and not radium B. This result can be explained if, when the radium B impinges on the reflector, a small portion of it is scattered on to S, but the greater part remains on the reflector, and subse- quently gives rise to radium C, a small fraction of which is then directly projected on to the plate S. That the admixture of radium B with radium C on S is to be attributed to reflection is probable, since the matter reach- ing a surface by direct radiation from a wire coated with radium A consists only of radium B. An experiment was performed under these conditions, and the decay curve of the activity collected on a surface after an exposure of ten minutes to the radium A was obtained. The points lying on the curve A {Figure 2) were determined in this way, and we have seen that the curve itself was obtained by calcu- lation for these experimental conditions. In an experi- ment in which a plate was situated so as to receive radium B from a source of radium A, only after a number of reflections, the proportion of radium C reaching the plate was even greater than in the case already cited. The fact that in the case of a single reflection considered above, radium B and radium C reached the plate S in almost equal proportions was a little surprising ; for it has been shown that when a surface is coated with radium B, under normal conditions the number of atoms of radium C which succeed in escaping from the surface by recoil is only of the order of one thousandth of the total number formed.* The composition of the activity on the plate S

* Makower & Russ, r/iiL Mag., Jan., J910.

4 Makower, Scattering during Radio-active Recoil.

can therefore only be explained either if the quantity of radium B reflected at O is very small, or if the chances of recoil are greater under the present experimental con- ditions than in the previous experiments. The latter explanation seems to be the correct one, for we have seen that radium B and radium C reach the surface S in almost equal proportions, and the a-ray activity of the plate S was found to have about -^^^ the activity of the surface Q when tested 20 minutes after the recoil from the wire P had ceased. Now it can be calculated from these facts that, if a small fraction x of the radium B recoil-atoms reaching Q are reflected on to the plate S, the fraction of radium C recoil-atoms subsequently reaching S to the total number formed on O must be about lo.r. Taken in conjunction with the fact that the activity of O was only twenty times that of S, this result leads to the conclusion that the proportion of radium C atoms which succeed in recoiling from the surface O is greater than the fraction (one thousandth) previously obtained. Though it is not possible to be quite sure of this deduction from the above evidence, the conclusion is not unreasonable since the atoms of radium B deposited from the wire P by recoil are lightly distributed over the surface Q without any risk of being covered by surface films as might easily be the case with any other method of deposition. The whole question of the scattering of recoil-atoms is at present receiving more careful examination.

]\TancJiestey Memoirs , Vol. /:-. (1910), No. 3.

III. The Development of the Atomic Theory : (2) The various Accounts of the Origin of Dalton's Theory.

By x^NDREW NOKMAN MELDRUM, D.Sc.

(Carnegie Kcsearrh Felloiv).

(Communicakd by Professoi- H. B. Dixo/i, M.A., F.R.S.) Received June, igio. A'cad Novetnher ist, igio.

The origin of Dalton's theory remains one of the outstanding problems in the history of chemistry. Yet the amount of material at hand for the study of the subject is considerable. Dalton's note-books, discovered within the last twenty years in the rooms of the Man- chester Literary and Philosophical Society, contain material of the highest value for the purpose. Also, there are on record important accounts of the genesis of the theory by three different persons. One is given by William Charles Henry, another by Thomas Thomson, and another by Dalton himself Although there are yet other accounts in existence, these three are the only ones that need be considered in detail here.

One of the principal results of this paper is to show that these various narratives came, originally, from Dalton himself. In the nature of the case, this is what was to be expected. At the same time the discrepancies between these accounts have to be explained. In the course of the paper it will become more and more evident that the person responsible for them is Dalton.

December lyth, igio.

2 Meldrum, Development of the Atomic Theory.

I. The Itifliience of J. B. Richter.

William Charles Henry held a conversation with Dalton on the subject of the origin of the theory, in which special importance was given to the influence of J. B. Richter. " The speculations which gave birth to the atomic theory were first suggested to Mr. Dalton by the experiments of Richter on the neutral salts ... a table was formed exhibiting the proportions of the acids and the alkaline bases constituting neutral salts. It immediately struck Mr. Dalton that if these saline com- pounds were constituted of an atom of acid and one of alkali, the tabular numbers would express the relative weights of the ultimate atoms. These views were con- firmed and extended by a new discovery of Proust,"' &c.

This narrative received strong support from William Henry (the father of W. C. Henry), who held more than one conversation with Dalton on the subject. The following is part of a minute, dated February 13, 1830, of one of these conversations : — " Confirmed the account he before gave me of the origin of his speculations leading to the doctrine of simple multiples, and of the influence of Richter's table in exciting these views."^

The Henrys, father and son, are entitled to the fullest credence in this matter. Their acquaintance with Dalton was more intimate than that of any other man of science, Peter Clare excepted. W. C. Henry was in turn the pupil, the friend and the biographer of Dalton. In the preface to the Biography, he mentions with just pride Dalton's " almost lifelong friendship with my father, never shadowed by even a passing cloud " ; and he refers also to " his early favourable notice of and unceasing benevolent regard towards myself, thoughtfully mani-

' W. C. Henry, "Memoirs of Dalton," p. 84. - Ibid., p. 63.

Manchester Memoirs, Vol. Iv. (1910), No. 14. 3

fested in his last bequest to me of what he had most prized in Hfe." This was the bequest of all his chemical and philosophical instruments and apparatus. Other proofs of this friendship can easily be found. There is the dedication of Dalton's " New System of Chemical Philosophy " (vol. i., Part 2) to William Henry (along with Humphrey Davy), and of Henry's " Elements of Experimental Chemistry" (6th Ed., 1810) to Dalton. Again, Dalton took an opportunity in 1827 of acknow- ledging his friendship with William Henry. " It affords me great pleasure to acknowledge the continued and friendly intercourse with Dr. Henry, whose discussions on scientific subjects are always instructive, and whose stores are always open when the promotion of science is the object."^

There is no room for doubt that the reports of these conversations with Dalton are perfectly authentic. W. C. Henry states that he noted down Dalton's expressions " immediately after each lesson," and the passage which has been quoted, regarding the influence of Richter, is copied, he says, " verbatim from my own journal when his pupil."* Nevertheless, Henry knew there was something wrong. The date of his conversation with Dalton was February 5, 1824, and he says, "on reviewing in con- versation, after the lapse of twenty years, the labours of the past, Dalton himself may have failed in recalling the antecedents of his great discovery in the exact order of sequence"^

Again, the Richter story is strongly challenged by Thomas Thomson. "When I visited him in 1804 at Manchester both Mr. Dalton and myself were ignorant of

" "New System of Chemical Philosoph}-,'' vol. 2, p. 8, 1827. * Ibid., p. 84. ° Ibid., p. 86.

4 MFLDRU^r, Devdopiuoit of the. Atomic Theory.

what had been done by Richter on the same subject." Again, " Nobody knows better than myself that Dalton was ignorant of what Richter had done about ten years before him.'"' This shows conclusively that Dalton said nothing about Richter to Thomson.

Now that we have access, thanks to Roscoe and Harden's " New View of the Origin of Dalton's Atomic Theory," to the valuable material contained in Dalton's notebooks, we can carry the critical process further than Henry and Thomson did. The notebooks show, as Roscoe and Harden point out, that Dalton had been busily engaged during the year 1803 on the atomic theory, and that he was investigating the non-metallic elements then, and not Richter's acids and bases at all.

Dalton's knowledge of Richter can hardly have been due to anyone but Berthollet. Richter's work had been completely ignored till E. G. Fischer gave a resume of it, and thus made it known throughout Germany. Ber- thollet, by quoting this resume at the end of the " Essai de Chimie Statique," made Richter known throughout Europe. In the " Essai " Berthollet opposes Dalton's theory of "mixed gases," but Dalton made no reply till 1808 in the " New System of Chemical Philosophy." This helps to date his knowledge of Richter. If Dalton was slow to read new books, he was prompt in replying to criticisms of his theory. He kept up the defence of it in a series of papers which came to an end about October, 1805, without any mention of BerthoUet's objections having been made. It was presumably subsequent to this date that Dalton read the "Essai," and learnt of Richter's work. In the note-books the date of the earliest reference to Richter is April 19th, 1807.'' There is really no room for doubt that

*■' Pi-oc. Phil. Soc. Glasgow, vol. 2, pp. 86, 88, 1845-6. ' Roscoe and Harden, " New View of ^tlie Origin of Dalton's Atomic Theory,'" p. 79 ; see also pp. 7-10, 46, 91-94.

Munches ley Monoirs, Vol. Iv. (191OJ, No. %, 5

Dalton's declarations in 1824 and 1830 to one and the same effect regarding the influence of Richter must be set aside.-

2. The Conipositio}i of Marsh-gas and Olefiant Gas.

Thomas Thomson says that the theory first occurred to Dalton during his investigation of marsh-gas and olefiant gas. The discovery of the composition of these gases led to the discovery of the law of multiple propor- tion, and the theory was then devised in order to explain the law. His exact words are : —

" Mr. Dalton informed me that the atomic theory first occurred to him during his investigations of olefiant gas and carburetted hydrogen gas, at that time imperfectly understood, and the constitution of which was first fully developed by Mr. Dalton himself It was obvious from the experiments which he made upon them that the con- stituents of both were carbon and hydrogen, and nothing else. He found, further, that if we reckon the carbon in each the same, then carburetted hydrogen contains exactly twice as much hydrogen as olefiant gas does. This deter- mined him to state the ratios of these constituents in numbers, and to consider the olefiant gas a compound of one atom of carbon and one atom of hydrogen ; and car- buretted hydrogen of one atom of carbon and two atoms of hydrogen. The idea thus conceived was applied to carbonic oxide, water, ammonia, &c., and numbers were given representing the atomic weights of oxygen, azote, &c., deduced from the best analytical experiments which chemistry then possessed.'"^

This narrative has passed muster for many years, and is better known than any other. It was accepted with

■" Roscoe and Harden, loc. <■//.

" Tluimas Thomson, " History of Chemistry," vol. 2, p. 291.

6 Meldrum, Development of the Atomic Theory.

reservations by W. C. Henry'" and Angus Smith", and by Roscoe and Schorlemmer^' without objection. Owing to the large circulation of Roscoe and Schorlemmer's book, this version of the origin has decided the opinion of the generality of chemists. There is, nevertheless, the best reason for thinking that marsh-gas and olefiant gas did not have the effect which it assigns to them of leading to the theory.

Indeed, in i8ii, Dalton connected the theory in its early days with the oxides of nitrogen : — " I remember the strong impression which at a very early period of these inquiries was made by observing the proportion of oxygen to azote, as i, 2, and 3, in nitrous oxide, nitrous gas, and nitric acid, according to the experiments of Davy."^° Thomson must have seen the necessity of aban- doning the marsh-gas and olefiant gas story, for he said in 1850 : — "Dalton founded his theory on the analysis of two gases, namely, protoxide and deutoxide of azote." '■'

Dalton's work on marsh-gas appears in the note-book under date 6th August, 1804. Roscoe and Harden'^ point out that he had been busily engaged on the theory the year before. He had even arrived at the fundamental ideas of his system, and had constructed a table of atomic weights by September 6th, 1803.

Obviously, Thomson's account of the origin of the theory is untrustworthy, inasmuch as marsh-gas and olefiant gas had no part in the matter. The question arises, who is responsible for the error, Thomson or Dalton ? Before answering this question it is necessary

'" " Memoirs of DalLon," p. So.

^ ' " Memoir of Dalton,"' p. 231.

'- '• Treatise on Chemistry, Non-metallic Elements,'' p. 36, 1877.

** Nicholsoiis Joiii-ii., vol. 29, p. I43, 181 1.

' ■' Proc. Pliil. Soc. Glasgow, vol. 3, p. 140, 1850.

1^ Op. cit., p. 28.

Manchestef Memoirs, Vol. Iv. (1910), No. 3. 7

to consider carefully the relations between the two men and the circumstances under which Thomson's narrative arose.

Thomson, unlike the Henrys, was not a personal friend of Dalton. He had made an adverse criticism of a certain theory of which Dalton was the author, and the author had made a stiff rejoinder/"' He thereupon paid a visit to Manchester with the object of arriving at a full understanding of the matter in question. The date of the interview was August 27th, 1804, ^"d it was then, b\- a fortunate accident, that Thomson learnt of the chemical atomic theory of Dalton.

Again, it is certain that Thomson and Dalton were not subsequently in frequent communication with one another on the subject. The sketch of the theory, which Thomson published in 1807, was accompanied by the note : — " In justice to Mr. Dalton, 1 must warn the reader not to decide upon the notions of that philosopher from the sketch which I have given, derived from a few minutes conversation, and from a short written memorandum. The mistakes, if any occur, are to be laid to my account, and not to his ; as it is extremely probable that 1 may have misconceived his meaning in some points."''

Nevertheless, this footnote errs on the side of caution. Thomson's sketch of the theory, giving the first account of it ever printed, was based on notes of what Dalton told him, made during the interview, and only one phrase in it is open to objection. He showed both zeal and care in the matter, for it strongly interested him.

In the "History of Chemistry," published in 1831, Thomson says : — " I wrote down at the time the opinions which he offered, and the following account is taken

' '^ See Nicholson' s Joitni., vol. 8, p. 145, 1804 ; and Annals of Philo- sophy, vol. 4, p. 65, 1814.

^^ Thomas Thomson, "System of Chemistry," 3rd Ed., vol. 3, p. 425, 1807.

S Meldrum, Development of the Atomic Theory.

literally from my journal of that date.'"* Then comes an account of the atomic theory, and on that there follows the passage already quoted, connecting" marsh-gas and olefiant gas with the genesis of the theory. Here the question arises, is all this taken from the journal, both the sketch of the theory and of how the theory arose? Only an examination of the journal can settle this point, but I have not succeeded in ascertaining where it is kept, if, indeed, it is still in existence.

It must be admitted also that Thomson seems to become more and more positive regarding the genesis of the theory as time goes on. The account which I have been considering was published in 1831. Six years earlier he had advanced the same account in a more hesi- tating way : — " Unless my recollection fails me, Mr. Dal- ton's theory was originally deduced from his experiments on olefiant gas and carburetted hydrogen.'"'' Yet there is no intrinsic improbability that Thomson's recollection is correct. One cannot doubt that during the interview Dalton was much less interested in the question of the origin than in the theory itself If Thomson inquired about the origin, Dalton may have made the inquiry an opportunity of expounding the theory in terms of its latest triumph, namely, the composition of marsh-gas and olefiant gas.

3. The Amended Theory of^' Mixed Gases"

There remains for consideration the account which Dalton gave in a lecture (the 17th ofa series) at the Royal Institution of London, on the 27th January, 18 10. The

'" Thomas Thomson, " liisloiy of Chcmisliy," vol. 2, p. 287. '■'Thomas Thomson, " An Attempt to Estabhsh the First Principles of Chemistry by Experiment," vol. i, p. 11, 1825.

Manchester Memoirs, Vol. Iv. (1910), No. 3. 9

notes for it still exist in his own handwriting, and were found, along with his notebooks, in the rooms of the Man- chester Literary and Philosophical Society. He begins by discussing his physical atomic theory, which aimed at explaining the diffusion of gases. He entertained two diffusion hypotheses, the first of which originated in 1801, while an amended hypothesis, he says, was formed in the year 1805. He had not at first "contemplated the effect oi difference of size in the particles of elastic fluids." On consideration, he " found that the sizes must be different," and subsequently arrived at a different explanation of the mechanism of diffusion from the one he at first suggested.

He then introduces the subject of the chemical atomic theory : — " The different sizes of the particles of elastic fluids under like circumstances of temperature and pres- sure being once established, it became an object to deter- mine the relative sizes and zveigkts, together with the relative ?z«w<^^r of atoms in a given volume. This led the way to the combination of gases . . . other bodies besides elastic fluids, namely, liquids and solids, were subject to investigation, in consequence of their combining with elastic fluids. Thus a train of investigation was laid for determining the number and weight of all chemical elementary principles which enter into any sort of com- bination one with another." ■"

This narrative is certamly right on a vital matter. It recognises that Dalton had been using a physical atomic theory, from which he passed to a chemical one. Here there is a common ground of objection to the com- munications made by Dalton to Thomson and Henry respectively. They both ignore the connection, which certainly existed, between the physical and chemical theories. Thomson did not feel this defect, but Henry

■-" Roscoe and Harden, Op. cit., pp. i6 — 17,

lo Mrldrum, Development of the Atomic Theory.

did. While not denying the influence of Richter, he sums up the evidence on the subject as " unequivocally demon- strating the genesis of the atomic theory as a general ph)'sical conception from the study of matter in the aeriform condition, and its first practical application in chemistry to gaseous bodies, and emphatically to such as combine iyi multiple proportions."'^ There is no question here of extraordinary insight and discernment on Henry's part. He has simply considered the use Dalton had made of the physical atomic theory previous to forming a chemical one.

Roscoe and Harden have not paid sufficient attention to this. They say " It is . . . . well known that Dalton was an ardent adherent of the Newtonian doctrine of the atomic constitution of matter .... It now appears that it was from this physical standpoint that Dalton approached the atomic theory, and that he arrived at the idea that the atoms of different substances have different weights from purely physical considerations."-" There is really not sufficient justification for Roscoe and Harden's suggestion that they had found in Dalton's narrative a new view of the genesis of his atomic theory. The view is to be found in Henry, and might be formed by any person who should read with understanding Dalton's " Essay on the Constitution of Mixed Gases," which was written in i8oi, and published in 1802.

There is, however, a fundamental objection to Dalton's narrative. It has a deceptive appearance of being historical. Dalton was a pioneer of science, and a pioneer is a man who must make many mistakes and experience many failures. He has taken a number of different scientific movements and marshalled them, so that they are invested

-•' W. C. Henry, (9/.. at., p. 84.

■-'-' 1-loscoc and Ihirflen, ()/. cit., p. viii.

MancJiester Memoirs, Vol. Iv. (1910), No. 3. 11

with the appearance of a deliberate, strategical, irresistible advance. On examination his narrative, in spite of its grand air, is found to throw much less light than it pro- mises on the line of thought and train of investigation which he pursued. It is excessively abstract in tone, and avoids going into details and particulars and instances. It does not tell us what we want to know most, how and when Dalton arrived at the law of multiple proportions, and the part played by the law in the construction of the theory. Information on these matters is what is wanted, and anything else is beside the point.

Yet there is one novel element in Dalton's account. This is the suggestion that the formation of the chemical atomic theory took place subsequently to the amendment of the diffusion theory. But, as the notebooks show, the chemical theory was formed in 1803. Hence, Roscoe and Harden conclude that iSo5,the date which Dalton assigns to his amended diffusion theory, should be 1803.^ Reasons will be given later, in a paper on Dalton's physical atomic theory, for thinking that the narrative is doubtful on the only point on which it presents any novelty.

Conclusion.

There are in existence yet other accounts of this matter. One is given by Dalton's pupil, Joseph A. Ran- some,^* and another by Dalton himself. This was in the lecture which he delivered to the members of the Mechanics' Institute in Manchester on October 19th, 1835.''^ The main feature, which ^/Z the accounts have in

- => op. tit., p. 25.

-* W. C. Henry, Op. dt., pp. 220-222.

-* Manchester Times, October 25, 1835.

12 Meldrum, Developme7it of tJic Atomic TJieory.

common, is that each originated with Dalton. Thomson's narrative and Henry's and Ransome's were based on conversations with him, and there is no ground for impugning their accuracy any more than his good faith. The natural explanation of the existence of so many and various accounts is that Dalton was simply deficient in historical instinct. He did not perceive the difference between describing the genesis of his theory and ex- pounding the theory itself.

A man who makes history, as Dalton did, need not be a good historian. The account of the origin of the chemical theory in his own handwriting is no more satisfactory than the others which came from him at second-hand. Apparently, Dalton never had in his mind a precise view of how the theory developed, and when invited to give one he produced, on the spur of the moment, an account to which he did, or did not, adhere on the next occasion.

Manchester Memoirs, Vol. Iv. (1910), No. 4-

IV. The Development of the Atomic Theory: (3) Newton's Theory, and its Influence in the Eighteenth Century.

By Andrew Norman Meldrum, D.Sc.

( Carnegie Research Fellow).

( Commu?ncated by Professor H. B. Dixon. M.A., F.R.S.)

Received June, jgio. Read November ist, igio.

One of the great obstacles to a right understanding of the history of science, is the tendency of writers to let their attention be absorbed by a single individual, who thus engrosses the credit for important ideas and discoveries, to the neglect of deserving predecessors. This method, besides being unjust, gives a distorted view of the progress of science. For instance, Nernst, apropos of Dalton, remarks that the atomic hypothesis " by one effort of modern science, arose like a phoenix from the ashes of the old Greek philosophy"^ This sweeping statement ignores atomic speculation between the time of Lucretius and the nineteenth century. As if the atomic theory of Newton, for instance, were perfectly negligible !

This paper is written in the belief that the atomic tlieory has gone through a process of development from the time of Leucippus up to the present. The main con- clusions are that Newton made a contribution to the said process, that he did so under the influence of Descartes, and that he was, in turn, himself an influence in the eighteenth century. It is therefore divided into two parts : (i) The atomic theory of Newton, and (2) Newton's influence in the eighteenth century.

* Nernst, " Theoretische Chemie,"' Sth ed., p. 34. December ijth, igio.

2 Meldrum, Development of the Atomic Theory.

I. The Atomic Theory of Neivton.

In the seventeenth century the atomic theory is asso- ciated with the famous names of Francis Bacon (1561 — 1626), Rene Descartes (1596 — 1650), Pierre Gassend (1592 — 1655), Robert Boyle (1627 — 1691) and Isaac Newton (1642 — 1727).

Bacon recurs to the theory again and again in his philosophical writings, as if fascinated by it. At one time he entertained great expectations from the study of the atoms. " I know not whether this inquiry I speak of concerning the first condition of seeds or atoms be not the most useful of all, as being the supreme rule of art and power, and the true moderator of hopes and works."' This in the " Cogitationes de Natura Rerum," which is regarded as having been composed before the year 1605. I^^t he changed his mind on the subject, tending, as time passed, to become more and more distrust- ful of a priori reasoning. His mature judgment, as ex- pressed in the "Novum Organum," published in 1620, was that the atoms are an unprofitable study. " Men cease not . . . from dissecting nature till they reach the atom ; things which, even if true, can do but little for the welfare of mankind."'

Boyle, in this country, was the exponent of the atomic theory who brought it into repute. In the year 1659 he urged the "desirableness of a good intelligence between the Corpuscularian Philosophers and the chemists," * and this topic for some time afterwards he made a leading theme in his scientific writings. Within a few years of his first attempt he was able to say that he has "had the happiness

- Bacon's Works, ed. by Spedding & Ellis, vol. 5, p. 423. ' Op. cit., vol. 4, p. 68 ; or Nov. Org., I, aphorism 66. * Boyle's Works, ed. by Birch, vol. I, p. 227, 1744.

Manchester Monoirs, Vol. Iv. {igio). No. 4t- 3

to engage both divers chymists to learn and relish the notions of the Corpuscular Philosophy, and divers eminent embracers of that to endeavour to illustrate and promote the new philosophy by addicting themselves to the experi- ments and perusing the books of chemists."'' While on this subject, he mentions Descartes and Gassend con- stantly, and other philosophers hardly ever.

Descartes believed in the existence of atoms, and at the same time he denied that a void could exist. A subtle fluid occupied the space between the atoms, and even per- meated them. Hence the vortex motion which had been set up in the fluid could not but communicate itself to the atoms. An admirable description of the atmosphere, according to the Cartesian theory, is to be found in Boyle's " New Experiments, Physico-Mechanical, touching the Spring of the Air." "The restless agitation of that celestial matter, wherein these particles [of air] swim, so whirls them round, that each corpuscle endeavours to beat off all others from coming within the little sphere requisite to its motion about its own centre . . . their elastical power is made to depend . . . upon the vehement agita- tion . . . which they receive from the fluid ether that swiftly flows between them."" It is remarkably difficult to find in Descartes so good a description of his theory as thi.s.^

Descartes' denial that a vacuum could exist, it is plain from this, is not to be taken in the crudest sense. He never meant and never said that space is full of matter of the ponderable kind.'' He meant, surely, that in the

*• Op. lit., vfil. 2, p. 501. « Op. cii., vol. I, p. 8.

' CEuvres, ed. by Cousin, vol. 5, p. 159-162, 169-170. ^ Clerk Maxwell might well have emphasised this in his comment on "The Error of Descartes," in " Matter and Motion," article xvi.

4 M^L\M<\:'S\, Dere/opjncnt of the Atomic TJieory.

absence of ponderable matter, space is occupied by ether, " the celestial matter ; " in short, that " we have no means of producing an ether-vacuum."

A more conventional theory is due to the revival, by Gassend, of the Epicurean philosophy. His interest in this philosophy was such that for twenty years he devoted himself to the study of Epicurus, and Lucretius the Epicurean." Gassend sought to connect the atomic theory with both physical and ethical problems, for those were the days when natural and moral philosophy were studied by the same persons. He brought out three books on the subject, between the years 1647 and 1649, one of which, the " Syntagma Philosophiae Epicuri," was well known to Boyle.

Boyle learnt of the work through his friend Samuel Hartlib, who wrote to him, in a letter dated London, May 9th, 164S : "Your worthy friend and mine, Mr. Gas- send, is reasonable well, and hath printed a book of the life and manners oi Epiaii us, since your going from here. He hath now in the press at Lyons the philosophy of Epicurus, in which, I believe, we shall have much of his own philosophy, which doubtless will be an excellent work." ^^

There was then, as there is still, a tendency to regard Descartes and Gassend as opponents of one another on the principles of the atomic theory. Boyle mentions some "learned men as more favouring the Epicurean, and others (though but a few) being more inclinable to the Cartesian opinions." However, in one of his essays, he advises Pyrophilus to read the "learned Gassendus,\{\s

" For a study of the Lucretian philosophy, see "Lucretius, Epicurean and Poet," 2 vols., by John Masson. Chap, i, vol. 2, is devoted to Gassend, of whom it gives a most interesting account.

'" Boyle's Works, ed. by Hirc'n, vol. 5, p. 257, 1744.

Manc/iestcr JMcjiioirs, Vol. Iv. (1910), No. 4. 5

little SyntagJiia of Epicurus' philosophy, and that most ingenious gentleman, Mons. Descartes, his principles of philosophy." " He did not see any necessity to ally himself with one party or the other. " Notwithstanding those things, wherein the atomists and the Cartesians differed, they might be thought to agree in the main, and their hypotheses might, by a person of a reconciling disposition, be looked on . . . as one philosophy." ^^

Science has often gained immensely by a wise limita- tion of the problem to be solved. Descartes' theory, that space is pervaded by an ethereal fluid, and that ordinary matter consists of atoms swimming in the ether, is formally complete, and has to be adopted sooner or later. Yet Gassend's theory, which is incomplete, since it ignores the ether, and concentrates attention on the atoms, proved more helpful to science in the first instance. Newton was more inclined to Gassend's way of thinking than to Descartes'. In the " Principia" he would not consider the mechanism of gravitation, and in the course of his atomic speculations he almost leaves out of account the means by which chemical attraction arises. Nevertheless, Newton was influenced by Descartes.

The Cartesian natural philosophy was predominant throughout Europe for the most part of the seventeenth century, and, in the eighteenth, it was supplanted by the Newtonian philosophy, as expounded in the " Principia." The two philosophies being opposed to one another, no one apparently has reflected how much Newton may have been indebted to Descartes. The mere fact that Cartesianism was dominant during the seventeenth century means that Newton must have made himself master of that system of nature. Presumably

'1 op. fit., vol. I, p. 194.

12 op. cit., vol. I, p. 227-228.

6 Meldrum, Developmoit of the Atomic Theory .

then, whatever was sound in Descartes he retauied and assimilated. Boyle and Hooke had studied Descartes, and Newton studied all three. In a letter to Hooke, dated Feb. 5th, 1675/6, on the subject of light, he admits his indebtedness to others. " You defer too much to my ability in searching into this subject. What Descartes did was a good step. You have added much several ways, and especially in considering the colours of thin plates. If I have seen further, it is by standing on the shoulders of giants." ^'"

Newton, in his speculaiions on the disintegration of atoms, in Query 31 of the "Optics," had no unusual physical phenomenon in viev.' at the time. He was simply improving on Descartes," whose theory on the subject seems crude enough.''

In contrast to the speculative topic of disintegration, another problem which interested Newton was a perfectly concrete one. This was Boyle's law, made known in the year 1662, that the volume of a given quantity of air is inversely proportional to the pressure. Newton's theory of gravitation was based on the assumption that every particle of matter attracts every other particle. In ex- plaining Boyle's law he made the very different assumption that air is composed of particles which repel one another.

This conception of the atmosphere, as being composed of " particles mutually repulsive," was in all probability derived from Descartes. Boyle, in the passage already quoted, where he explains the Cartesian theory, says that in the air, "each corpuscle endeavours to beat off all others from coming within the little sphere requisite to its motion about its own centre."

^•'' Brew.ster's " Life of Newton," vol. I, p. 142. '■' CEuvres, ed. by Cousin, vol. 4, pp. 266-268.

^ ^ I am indebted to my friend, Mr. J. R. Partington, B.Sc, for pointing out to me that Descartes was the source of Newton's ideas on disintegration.

Manchester Memoirs, Vol. Iv. (1910), No. 4- 7

Newton proved that the air must obey Boyle's law, if the force of repulsion between its particles were in- versely proportional to the distance between them. He does not mention Boyle, or the air, but puts the matter in the most abstract way, by advancing the following propo- sition : — " If the density of a fluid which is made up of mutually repulsive particles, is proportional to the pressure, the forces between the particles are reciprocally propor- tional to the distance between their centres. And vice versa, mutually repulsive particles, the forces between which are reciprocally proportional to the distance between their centres, will make up an elastic fluid, the density of which is proportional to the pressure." ^^

Newton does not draw any inference as to the nature of the atmosphere. " All these things are to be under- stood of particles whose centrifugal forces terminate in those particles that are next them, or are diffused not much further. We have an example of this in magnetical bodies. .... Whether elastic fluids do really consist of particles so repelling each other, is a physical question. We have here demonstrated mathematically the property of fluids consisting of particles of this kind, that hence philosophers may take occasion to discuss that question."

This proposition, along with its proof in the " Principia,'' is the earliest instance of the mathematical treatment of the atomic theory. Svante Arrhenius declares that "the atomic theory remained in the hypothetical state for about 2,300 years, as no quantitative conclusions were drawn from it till the time of Dalton." '" This statement entirely ignores Newton's explanation of Boyle's law in terms of atoms, as well as certain workers in the eighteenth century, who were under Newton's influence.

^'^ " Principia," Book 2, prop. 23.

^^ Arrhenius, " Theoi'ies of Chemistry, Eng. trans., p. 15.

8 Melurum, Developuicni of the Atomic Theory.

II. Netv ton's Influence in the Eighteenth Century.

In the last quarter of the eighteenth century a very- remarkable attempt at an atomic theory was made by two Irishmen, by name Bryan Higgins and William Higgins. The object of the second and concluding part of this paper is to show that the theory advanced by Bryan Higgins and amplified by William Higgins can be under- stood only when regarded as springing, under the peculiar conditions of the time, from Newton's theory. These conditions were (i) the knowledge, due to Priestley, of different kinds of gases, and (2) the new light which Lavoisier threw on chemical composition consequent on Priestley's discovery of oxygen.

The senior of the two men,'" Bryan Higgins (1737- 1820) was self-taught in chemistry, and his career proves him to have been the best all-round man among the English-speaking chemists of his day. His " Experiments and Observations concerning Acetous Acid" (1786) is a record of a very thorough investigation in the field of organic chemistry, in the course of which he discovered the substance acetamide. As a technical chemist his reputation was wide. He spent about four years (1797- 1802} in the West Indies, investigating the manufacture of Muscovado sugar and rum. He was a pioneer in the practical teaching of chemistry, and gave instruction in the subject for some twenty-three }-ears (1774-1797) in his School of Practical CJieniistry in Greek Street, Soho, London. His minor discoveries include that of the musical note which can be got on burning a jet of hydrogen in air (1777}.

'* For fuller information regarding them, see Brit. Assoc. Rep., Dublin meeting, 1908, p. 668, and New Ireland Review, 1910, n.s., vol. 32, pp. and 350-364.

Maiidicster Memoirs, Vol. Iv. (1910), No. 4- 9

His most important publication, in connection with the atomic theory, is a " Philosophical Essay Concerning Light" (1776). This essay is very different from what it purports to be. It contains only a fragment — all that was ever published — of the essay on light that Higgins had designed. The major part of the book is simply an expansion and exposition of a " Syllabus of Chemistry," which he had published earlier, in 1774 or 1775, and which is also prefixed to the Essay.

Higgins had gone to Newton for inspiration : the "Philosophical Essay" is full of quotations from the " Opticks." Nor need there be any wonder at Higgins making his approach to the study of light by way of chemistry, since Newton's views on chemical subjects are to be found in the "Opticks" more than in any other of his books.

The discovery of new facts always gives a stimulus to speculation. The impulse in Higgins' case came from Joseph Priestley, who showed in the year 1775 that the alkaline substance ammonia, and various acids, hydro- chloric, for instance, can exist in the gaseous state. Higgins thereupon proceeded to adapt the Newtonian conception of a gas to the processes of chemistry. Gaseous particles of the same kind were " mutually repul- sive," but what should happen in case acid and alkali were brought together? Higgins said that the acid particles and the alkaline attracted one another, and formed a neutral salt by combining /^^f/^V■/(^ with particle.

Higgins laid great stress on this force of repulsion between particles of the same kind. He thought an acid and an alkali must combine with one another in one proportion only, a combination of two particles of acid and one of alkali, or two of alkali and one of acid, being precluded, because the two similar particles

10 Meldrum, Development of tJie Atomic TJieory.

must repel one another. On this line of thought he finds the answer to his own question : — " Why do many salts crystallise nearly neutral in a liquor con- taining a superabundant quantity of acid and \sic'\ of alkali?" Further, on the supposition that particles of water and of acid attract one another, as also particles of water and of alkali, he thought he could account for the water of crystallisation found in many salts, so he explains " why much water doth combine in the crystals of most neutral salts, and why this water of crystallisation separates from the superfluous acid or alkali, and in- troduces little or none of either into the crystals." ''

In short, on the basis of Newton's theory of a gas, Bryan Higgins taught that chemical combination takes place between acid and alkali in a definite and single proportion. He went little further, if any, with these speculations. His progress must have been greatly hampered by his belief, to which he adhered till about the year 1792, in the phlogiston theory of chemistry, and by his belief in the existence of seven chemical elements, namely, earth, water, air, acid, alkali, phlogiston and light.

William Higgins (i769?-i825) was trained in chem- istry by his uncle. He assisted Dr. Beddoes in the teaching of chemistry at Oxford (1787), and acted as chemist to the Apothecaries' Hall of Ireland (i 791 -1795), and then to the Royal Dublin Society (1795-1825). He was a Fellow of the Royal Irish Academy and of the Royal Society of London.

He did not long suffer from the disadvantages of the phlogiston theory, for he was one of the first to

^^ Biyan Higgins, "A Philosophical essay concerning Light," pp. 201- 208, 212-213.

Mancliester Memoirs, Vol. Iv. {igio), No. 4. ii

abandon it — in 1785, he says — and was absolutely the first to write against it in the English language. His " Comparative View of the Phlogistic and Anti-phlogistic Hypotheses" (1789) is primarily a refutation of the phlogiston theor}'. Incidentally, it shows that he had been carrying on experimental work of his own, and also that he had improved on his uncle's speculations. Out of atoms and molecules he fashioned a theory of chemical combination and chemical dynamics as well, so that his book is remarkable as containing the first attempt at a comprehensive system of chemistry, based on the atomic theory.

William Higgins regarded the atom of a gas as a hard particle surrounded by an "atmosphere of fire.""" He believed firmly that chemical combination occurs in definite proportions, and supposed that it occurs, in the first place, atom with atom. He regarded the molecule of water as formed by the linking of one atom of hydrogen with one of oxygen. " Water is composed of molicules formed by the union of a single ultimate particle of dephlogisticated air to an ultimate particle of light inflam- mable air . . . they are incapable of uniting to a third particle of either of their constituent particles."^ In short the formula OH expresses his conception of the molecule of water.

William Higgins was better acquainted with the facts of chemical composition than his uncle, for he did not believe in phlogiston, and he recognised oxygen as one of the elements. He was aware of a number of cases in which elements combine in more than one proportion, and in such cases continued to apply the atomic theory.

** " Comparative View of the Phlogistic and Antiphlogistic Hypotheses," pp. 14, 37, 81, 133.

Ibid., p. 37.

12 Meldrum, Development of the Atomic Theorr.

He thought an element R must form oxides in the order RO, RO„, RO3, etc. Thus he regarded sulphurous acid virtually as SO, and sulphuric acid as SOo."'' He recog- nised five oxides of nitrogen, and regarded them as NO, NO„, NO.„ NO4, and NOe."' These ideas of chemical composition are based on the assumption that similar atoms repel one another, an assumption which is also the basis of his system of chemical dynamics. His argument was that because of this force of repulsion, the compound RO is more stable than RO2, RO, than RO,., and so on.

The line of thought thus opened by the Higginses afterwards proved extremely valuable, but it was not followed up at the time. William Higgins' book, pub- lished in 1789, and re-published in 1791, was read as a contribution to the phlogiston and anti-phlogiston con- troversy. That was the absorbing topic in science then, and nothing else could be duly attended to.

The history of this eighteenth century movement proved a difficult problem in the succeeding century. It occupied the attention at different times of such persons as William Charles Henry, R. Angus Smith, and, in collaboration, Roscoe and Schorlemmer. There was also a long and doubtful controversy regarding the relative merits of William Higgins and John Dalton, the discussion of which is left to a future paper.

Angus Smith's estimate of Bryan Higgins is a vastly different one from that advanced in this paper. His main conclusions are, that Bryan Higgins' " opinions on atoms might have been held by the ancients,"'* and " that his theory was not clear, or he would have been led by it to

--Ibid., pp. 36-37.

•'" Ibid., pp. 132-135, 165.

■^* R. Angus Smith, "Memoir of Dalton,'' p. 175.

Manchester Memoirs, Vol. Iv. {\gio), No. 4. 13

decide on the necessity of fixed composition as a result. But we obtain no results affecting chemical philosophy "'^ In this paper I have shown that Bryan Higgins' theory, far from being " ancient," is a development of Newton's, and that instead of his theory being obscure, and leading to confused ideas regarding chemical composition, it led to a view of the doctrine of fixed proportion, of which the fault was that it was too narrow and rigid.

This difference of opinion, great and hopeless as it may seem, admits of the simplest explanation. Smith's estimate is based upon the" Syllabus" of the year 1775, and upon certain incidental remarks on atoms which he found in the book on "Acetous acid." He was not acquainted with the "Philo-sophical Essay on Light," which assuredly is not the place where one should expect to find the chemical speculations and ideas regarding atoms, of which nevertheless it is full. Had Angus Smith read this book he must have i)erceived the clue to the Higgins' ideas, namely, the connection with Isaac Newton. He must then have seen that Bryan Higgins was the first to explain the constant chemical composition of salts in terms of atoms, and that his theory was only too definite and rigid, for it led him to maintain that an acid and an alkali could combine in only one proportion, namely, atom with atom.

W. C. Henry, in his estimate of William Higgins, shows the fatal weakness of failing to see the basis of the theory. Having given Higgins' views regarding the atomic composition of the oxides of nitrogen, he remarks : " It is evident that Mr. Higgins was guided by no fixed and uniform principle, in assigning the atomic constitution of the above compound bodies."-'^' This verdict also •-» Ibid., p. 173.

'-'• W. C. Henry, " Memoirs of Daltoii," p. 77.

14 Meldrum, Development of tlic Atomic Theory.

must be set aside. No great penetration of mind is required to divine "the fixed and uniform principle" on which Higgins proceeded in assigning the atomic composition of substances. Although he does not himself mention Newton, there is no room for doubt that Newton's conception of "particles mutually repulsive" w^as the germ of the theory. Bryan Higgins, who was a student of Newton, made use of this conception, and he communicated it to his nephew. The indebtedness of the nephew to the uncle is as plain as the indebtedness of the uncle to Newton.

There remains now for consideration a remark by Roscoe and Schorlemmer, that "all upholders of an atomic theory" previous to Dalton, "including even [William] Higgins, had supposed that the relative weights of the different elements are the same."-'^

This is a sweeping assertion, of which no proof has ever been offered. One can hardly believe that Newton expressed such an opinion, and it is certain that William Higgins did not. Regarding the oxidation of tin, he supposed that lOO grains of the metal may combine with 7|- or with 15 grains of oxygen.'""^ But since he held the oxidation series of an element to be RO, RO,, RO., etc., his figures for tin mean that the atom of the metal was supposed to be much heavier than one atom, or even two of oxygen. Possibly Roscoe and Schorlemmer's statement is based on the case of oxygen and sulphur, which Higgins held to have the same atomic weight. But this conclusion of his depends for one thing on the supposition that the molecule of sulphurous acid (the substance SO2, not H.SOg) is com- posed of one atom of each element, and for another on

-" Koscoe and Schorlemmer, " Non-Metallic Elements," p. 35, 1905. "■"* "Comparative View,'" p. 275.

Manchester Mei)ioirs, Vol. Iv. (19 lo), No. 4. 15

the experimental fact that the acid is formed by the union of equal weights of the two elements. Higgins proved, quite correctly on his supposition, that the atomic weights of sulphur and oxygen are equal. But proof and assumption are two very different things. Surely it is one thing to prove a result in a particular case, and quite another to assume the result in general.

Manchester Memoirs, Vol. Iv. ( 1 9 1 1 ), No. 5-

V. The Development of the Atomic Theory : (4) Dalton's Physical Atomic Theory.

By Andrew Norman Meldrum, D.Sc

{Carnegie Research Fellow). (Communicated by Prof. H. B. Dixon, Af.A., F.R.S.)

Received October, igio. Read January loth, igii.

In the opinion of the author, many of those who write about Dalton let their attention be engrossed too much by his chemical work. For, in order to understand even the chemical work, it must be kept in mind that Dalton began his scientific career as a meteorologist, that this led him to become a student of physics, and that he took up the study of chemistry subsequently.

The following paper shows that Dalton's physical atomic theory was the first great achievement of his career. It was based on his experimental work, and theory and work together, as soon as published, aroused, in his own words, the " attention of philosophers throughout Europe."

The physical atomic theory, otherwise the theory of " mixed gases," is specially interesting because it marks a stage in the development of Dalton's ideas. Both it and the experiments connected with it arose out of the meteorological observations and studies of his early life. It reveals him as a student of Newton, and as the up- holder of a physical atomic theory years before he formed the chemical one.

The present paper is divided into three parts : — I. Dalton's theory of " mixed gases "; II. The beginning and course of Dalton's experimental work ; III. The two forms of the physical atomic theory and the dates of their origin.

March yi/i, igii.

2 Meldrum, Development of tJie Atomic Theory.

I. DaLTON'S theory of " MIXED GASES." The question at issue.

One of the burning questions in science, at the begin- ning of the nineteenth century, was that of the constitution of " mixed gases." The question could hardly have been discussed much earlier, much less been settled, because the existence of gases, different from atmospheric air and from one another, had not been fully recognised till after the discovery of oxygen in 1774.

The properties of gases are accounted for now by the Kinetic Theory, but this was not established till after the middle of the century. Apart from this theory, men of science explained matters as best they could. The problem naturally arose in connection with the atmosphere, the nitrogen and oxygen of which, although they have different specific gravities, do not separate from one another. Two opinions, says Dalton, arose on this matter : the one supposed the two fluids were " merely mixed together, but assigned no reason why they do not separate . . . . The other supposes a true chemical union to exist between the two, and thus obviates the difficulty arising from the consideration of specific gravity.^ " The first of these opinions was held by a few isolated indi- viduals. Strange as it must seem now, the chemical explanation of diffusion was not only widespread amongst men of science, but was quite the predominant one.

The germ of Dalton s theory.

Dalton had early shown a tendency in the direction of

a mechanical explanation of the state of the atmosphere.

The " Meteorological Observations and Essays " published

in i793CGntains, as he pointed out many years afterwards,

"^Manchester Memoirs, [i], vol. 5, p. 538, 1802.

Manchester Me7Hoirs, Vol. Iv. {igii), No. ^. 3

" the germs of most of the ideas which I have since expounded more at length in different essays, and which have been considered as discoveries of some importance. For instance, the idea that steam or the vapour of water is an independent elastic fluid .... and hence that all elastic fluids, whether alone or mixed, exist indepen- dently."' He was probably influenced most by Deluc in forming this opinion, but other persons, including Bryan Higgins and Pictet, had expressed views more or less the same as Deluc's.

Da/ ton's theory of mixed gases.

Thus Dalton had early regarded the constitution of mixed gases from the physical point of view. In the year 1801 he formed a precise theory of his own, which he explained and maintained publicly. The paper in which he describes it, forms one of the set of four experi- mental essays, which, Dalton himself said, " drew the attention of most of the philosophers of Europe."

He put his theory in the following way : " When two elastic fluids, denoted by A and B, are mixed together, their is no mutual repulsion amongst their particles, that is, the particles of A do not repel those of B, as they do one another." ' At first the doctrine was not understood, and Dalton had to make further efforts to throw light upon it. His hypothesis meant that while gaseous particles of the same kind repelled one another, there were no forces, whether of repulsion or attraction, between particles of different kinds. Particles of one kind could offer only a passive resistance to the motion of another kind of particles, and acted only as temporary obstacles, in the same way as the pebbles in a stream

- " Meteorological Observation and Essays," 2nd Ed., p. v. (1834). ^ Manchester Memoirs, [i], vol. 5. p. 536, 1802.

4 Meldrum, Development of the Atomic Theory.

impede the flow of water. Hence, if two gases were brought together, they were found, sooner or later, to be uniformly mixed.

Dalton and the diffusion of gases.

After the theory had been explained, Dalton deemed it necessary to make new experiments on the diffusion of gases. Priestley, who originally drew attention to this phenomenon, was inclined to think it accidental in its nature. He thought that if " two kinds of air were put into the same vessel with very great care, without the least agitation that might mix or blend them together, they might continue separate."* Dalton's experiments, made with the simplest of apparatus, proved, in his own words, " the remarkable fact, tJiat a lighter elastic fluid ca)inot ?-est upon a heavier''^ The importance of this work, by which he established diffusion as a genuine property of gases, was recognised by Berthollet, who carefully repeated it."

Dalton was evidently much gratified by the agree- ment between his theory and the facts of diffusion. He concludes his memoir on diffusion with a note of triumph : — " The facts, stated above, taken together, appear to me to form as decisive evidence for that theory of elastic fluids which I maintain, and against the one commonly received, as any physical principle which has ever been deemed a subject of dispute, can adduce."^

Dalton^ s theory and the vapour of ivater.

Obviously, a special case of the mixed gases question is that of the water vapour in the atmosphere. The

* "Experiments and Observations, &c.," abridged, vol. 2, p. 441.

^ Manchestei- Memoirs, [2], vol. I, p. 260, 1805,

0 M^m. cCArceuil, vol. 2, p. 463, 1809.

' Manchester Memoirs, [2], vol. i, p. 270, 1805.

Manchester Mejiioirs, Vol. Iv. (191 1), No. 5. 5

^general, though not the universal opinion was, that this vapour was present in a state of combination with the air. The evaporation of water was thought to be an act of ■chemical combination between air and water, whilst boiling was a physical action. For since the atmospheric pressure prevents water from boiling at ordinary tem- peratures, it was thought that boiling was something ■quite distinct from evaporation, which takes place at all temperatures and pressures of the air. This distinction had received the sanction even of Lavoisier."

Dalton's theory had a special bearing on this subject. For the theory meant that the pressure of a mixture of gases is the sum of the respective pressures of the gases in the mixture. Dalton saw that the water vapour in the atmosphere had to be considered in terms of the pressure ■of the vapour. Experimentally he showed that the evaporation of water is proportional to the pressure of the vapour which the water gives off. At any given temperature there is a maximum which this pressure can reach, and water, whether in contact with the air or not, •can evaporate till the pressure of its vapour reaches this maximum and no further. On the other hand, air in which the water vapour is not at this maximum pressure can be cooled till the maximum is reached, and then, on further cooling, the water is deposited as dew. This led to observations of the " dew-point," which Dalton was the iirst to institute.

It was thus in the direction of Meteorology that Dalton's theory first bore fruit. In this science, as Play- fair has pointed out, it is easier than in any other to ^' accumulate observations, and more difficult to ascertain principles." At the beginning of the nineteenth century, hy pointing out the significance of the dew-point, Dalton * " Traite Elementaire de Chimie," 3rd ed., pp. 7-1 1, 39,

6 Meldrum, Development of the Atomic Theory.

succeeded in transforming hygrometry, and " raising it to. the rank of an exact science." "

Dalton's tlieory and Henrfs laiv.

Dalton's theory had been only a short time before the world, when it was reinforced in a remarkable way. It was found to have an important bearing on the solubility in water of a gas under various pressures. The study of this subject had been undertaken by William Henry^ already mentioned in the second paper of this series as a friend of Dalton.

Henry had discovered the law, which is now called after him, that at a given temperature, " water takes up the same volume of condensed gas as of gas under ordinary pressure." "^ The amount dissolved is propor- tional to the pressure. This, as Dalton pointed out to Henry, is a strong argument in favour of the view that solution is " purely a mechanical effect." If gas, in a state of absorption by water, is retained entirely by the incum- bent pressure, there is no need to call in the notion of chemical affinity.

Not only so, but in the matter of the solubility of a mixture of gases, Dalton's theory proved able to sustain a severe enough test. Henry found that each gas dissolved in water as if the others were absent, " Each gas," he concluded, " when dissolved in water, is retained in its place by an atmosphere of no other gas but its own kind." " This is precisely what was to be expected from Dalton's theory.

Henry had opposed the theory when it was first made known. He now wrote Dalton a letter, which was read

° See W. C. Henry, " Memoirs of Dalton," p. 226. I'' JVu'I. Trans., p. 41, 1803. ^^ Nicholson s Joiirn. , [2], vol. 9, p. 126, 1804.

Manchester Memoirs, Vol. Iv. (191 1), No. 5. 7

before this Society and then published, expressing his entire satisfaction with it. "In the discussions... which took place in the Society on your several papers, the doctrine of mixed gases was opposed by almost every member interested in such subjects, and by no one more strenuously than myself I am now satisfied that... your theory is better adapted than any former one, for explaining the relation of mixed gases to each other, and especially the connection between gases and water." '■

This support must have been specially gratifying to Dalton, in view of the keen opposition and criticism which the theory was receiving in other quarters. It probably confirmed and enhanced the "almost life-long friendship " between the two men, which is referred to repeatedly in this series of papers.

The ''' mixed gases'' controversy.

The controversy which was aroused by Dalton's theory of mixed gases affords proof at once of the interest taken in his mechanical explanation of the phenomenon, and of the tenacity with which the chemical explanation was adhered to. The view that air is a chemical compound was maintained with a persistency which is hardly credible now, and which throws into relief the originality and vigour of mind which Dalton showed in forming and urging a wiser view. The balance of opinion was against him, for his opponents included Claude Louis Berthollet, Thomas Thomson, John Gough, John Murray, and Humphry Davy.

Dalton's contention, that the diffusion of gases is a physical phenomenon, was at length fully and finally recognised in the Kinetic Theory of Gases. Meantime Dalton had to do his best in the circumstances, and the

^- NicholsoiC s Journ., [2], vol. 8, p. 297, 1S04.

8 Meldrum, Developwcut of the Atomic Theory.

particular mechanism by which he accounted for diffusion proved specially vulnerable/"

The most eager critic of the mechanical explanation was Gough. He wrote numerous letters and essays against it, which were answered by Dalton, and on one occasion by Henry. One of his criticisms was acute. If, as Dalton supposed, the particles of oxygen in the atmosphere have no action on the particles of nitrogen, and vice versa, this must affect the transmission of sound. Gough said the oxygen must transmit one sound wave and the nitrogen another, each with its own velocity, so that at a sufficient distance a sound should be heard double.

Berthollet, in his " Essai de Chimie Statique," shows himself a whole-hearted believer in the chemical theory. " It appears to me incontrovertible, that it is a true chemical action which produces the solution of liquids in gases, and evaporation."" He was unfavourably im- pressed by the diagram appended to the " Mixed Gases " Essay, in which Dalton exhibits particles of oxygen, nitrogen, water and carbon dioxide existing in the atmosphere independently of one another. ^^ " A diagram in which Dalton has attempted to show how different gaseous molecules may be disposed in the same space, is... only a figment of the imagination."^"

Thomas Thomson's interest was roused to a high pitch by Dalton's theory. Whilst expressly withholding his assent to it, he noticed it in edition after edition of

1" As a matter of fact, Dalton did for years believe that " portions of gas of different kinds behave to each other in a different manner from portions of gas of the same kind . . . whereas there is no difference between the two cases." Clerk Maxwell, " Theory of Heat,"' loth ed., pp. 28-29.

1* Op. cit., § 164.

^^ Manchester Memoirs, [i], vol. S, p. 602, 1802.

i« Op. «Y.,§244.

Manchester Memoirs, Vol. Iv. ( 1 9 1 1 ), No. 5- 9

his " System of Chemistry." Dalton's reply to the criticism in the second edition had a notable consequence. Thomson visited Manchester in order to get an explana- tion of the theory from the author himself, and it was on this occasion that Dalton told him about the chemical atomic theory.

II. The beginning and course of Dalton's

EXPERIMENTAL WORK. The Beginning.

Dalton did not begin original experimental work till 1799, when he was thirty-three years of age, and had been six years in Manchester. Up to then he had confined himself to work of observation, chiefly in meteor- ology. The first paper in which his own experiments occupy a considerable space is his memoir on the power of fluids to conduct heat. It was read before this Society on the 12th April, 1799.

A previous paper of his, read six weeks earlier, is of quite another stamp. The title of this is as follows : — " A paper, containing Experiments and Observations to determine whether the quantity of Rain and Dew is equal to the quantity of water carried off by the rivers and raised by Evaporation ; with an inquiry into the origin of springs." Now, not only are the experiments recorded in this paper hardly worthy of the name, but the subject itself is of the nature of a forlorn hope. Dalton could not have embarked on such a hopeless inquiry as this, if he had been accustomed to experimental research, and had experi- enced the advantages to be gained simply by limiting the scope of an investigation. This paper, therefore, marks the end of the first stage in his scientific career. By April of the year 1799 he was in the full swing of experimental work.

lO Meldrum, Development of the Atomic Theory.

Experiments connected with the vapour pressure of water.

A paper which Dalton read April i8th, 1800, marks another stage on the way. The title, which is significant of much, runs as follows : — " Experimental Essays, to determine the Expansion of Gases by Heat, and the maximnm of steam or aqueous vapour, which any gas of a given temperature can admit of ; with observations on the common or improved Steam Engines."

On this title four remarks may be made, (i) Dalton had arrived by April, 1800, at the idea, which forms the central fundamental conception of the second and third of the "Experimental Essays" of October, 1801, of the vapour pressure of water. He had begun to con- sider other gases besides the air, and knew that the maximum of water vapour in any gas is independent of the nature of the gas. It was in order to show this at different temperatures that he began to measure the " expansion of gases by heat."

(2) There is a practical connection between the expan- sion of gases by heat, and the original topic of the water vapour in the atmosphere. Dalton's explanation of the ■discrepancies betv/een the results of earlier workers on the subject is that it " arose from the want of due care to keep the apparatus and materials free from moisture." ^'^

(3) This paper, although passed for publication by the Society, never appeared. Nothing remains of the " Obser- vations on the common or improved Steam Engines."

(4) Perhaps Dalton had discovered by April, 1800, what we know as Charles' law, that different gases have the same expansion by heat. But he does not make this claim himself. The law forms the subject of the fourth of the " Experimental Essays," and this fourth essay,

^' Manchester Memoirs, [i], vol. 5, p. 596, 1802.

Mauckesier ATonoirs, Vol. Iv. (191 1), No. 5. 11

though usually dated October, 1801, was, as a matter of fact, not read then as the first three were before this Society.

Later developments.

Between the paper of April, 1800, and the " Experi- mental Essays" of October, 1801, Dalton took up the study of only two additional topics. One of these, the vapour pressure of other liquids than water, was a natural outcome of previous work, and calls for no special com- ment here. The other was that of the explanation of the phenomena of mixed gases. This, a large topic and not an experimental one, is discussed in the last section of this paper. But here is the place to point out that Dalton's reflections on this subject led to two experi- mental inquiries of the greatest consequence. One of these, already mentioned in this paper, was the study of the diffusion of gases. The other was the determination by Dalton of the composition of the atmosphere, the outcome of which, as will be shown in the next paper, was the formation of the chemical theory.

III. The two forms of the physical theory

AND the dates OF THEH^ ORIGIN.

The date of the first diffusion hypothesis.

Dalton, in the Introduction to his set of four "Experi- mental Essays" of October, 1801, explains that this theory of mixed gases was arrived at after his other results. " The first law \_i.e., the mixed gases theory] which is as a mirror in which all the experiments are best viewed, was last detected, and after all the particular facts had been previously ascertained." ^^

^* Manthcstcr Memoirs, [i], vol. 5, p. 536.

12 Meldrum, Dcvclopmen t of the A torn ic T/ieorj '.

There is no reason to question this statement. It is true that Dalton's historical narratives, as has been shown in the second paper of this series, cannot be accepted at their face value. But this is a contemporary statement, and, as such, must receive a considerable degree of credit.

The physical theory was formed between April, 1800, and September of the following year. There is no hint of it in the title of the paper '.vhich Dalton read on the 1 8th April of the earlier year. Again, the date of the first sketch of the theory, which he sent to NicJiolson's Jotirnal, is the 14th September, 1801, and the theory can hardly have arisen earlier than August. It is true that Angus Smith assigns the reading of the essay " On the Constitution of Mixed Gases" to July 31st, and October 2nd and i6th for the reading of the 2nd and 3rd essays respectively.'^ But the dates mentioned at the head of the papers in the MancJiester Memoirs, are the 2nd, i6th, and 30th October. Dalton must have known the dates on which his own papers were read, and as the author he was interested in not dating them later than was neces- sary. In the Minute-book of the Society the title of each of these papers was entered on a left hand page, and the date and other particulars of the meeting at which the paper was read on the right hand page. Angus Smith has made the slip, which one can easily understand, of assigning the reading of a paper to the meeting minuted on the previous page.

The influence of Neivton on Dalton.

The theory was formed under a new influence. Between April, 1800, and August or September, 1801

^" Angus Smith, "Memoir of Dalton," p. 254. These are not the only wrong dates in his list of Dalton's papers.

Manchester AIe})wirs, Vol. Iv. ( 1 9 1 1 ), No. 5. 1 3.

Dalton came under the stimulus of Newton's atomic theory. Everything goes to show that this had a great effect on him. He hardly mentions Newton in his early writings. In 1801, and subsequently, he quoted Newton on every suitable occasion, and in particular he mentions the 23rd Proposition of the 2nd Book of the " i'rincipia " at least five times. The mutually repulsive particles of this proposition play their part in Dalton's theory. The wording of it shows this : — " When two elastic fluids, denoted by A and B are mixed together^ there is no mutual repulsion amongst their particles ;, that is the particles of A do not repel those of B, as they do one another." ^°

Dalton's theory is a true development of the theory of Newton, in respect that it is a static one, representing the atoms as being, ultimately, at rest among themselves. If, as was shown in the 3rd paper of this series, Newton, in forming his theory deliberately set aside the dynamic ideas of Descartes, it is to be remembered that these ideas at length found expression in the Kinetic Theory of Gases.

The amended diffusion hypotliesis.

As already stated in the second paper of this series, Dalton explained in a lecture which he gave in 18 10, that he had not at first contemplated the effect o{ difference of size in the particles of elastic fluids. But he reflected that if the sizes be different, then on the supposition that the repulsive power is heat, no equilibrium can be established by particles of different sizes pressing against each other." On consideration, he found "that the sizes must be different ; " " thus," he concludes, " we arrive at the reason for that diffusion of every gas through every other gas,

-" Manchcsier i]Ieiiioirs, [l], vol. 5, p. 536, l8o2.

14 Meldrum, DevclopDient of the Atomic Theory.

without calling in any other repulsive power than the well known one oi heat" This, he says, occurred in 1805.°^ In later life, Dalton gave up this amended hypothesis, and reverted to his original one.™ But in 1808 he ex- pounded them both in the " New System." This may seem inconsistent of him, inasmuch as the two hypotheses are different from one another. Yet they are both forms of the physical atomic theory. Dalton's consistency lies in his adherence to a mechanical hypothesis in contrast to a chemical one. The question of the precise mechanism was subsidiary, and the mixed gases controversy turned entirely on the theory which Dalton advanced in 1801. No one took any notice of his change of front. It has, therefore, not been necessary to consider the amended diffusion hypothesis till now. The hypothesis is less important for its own sake than in its bearing, or supposed bearing, on the development of Dalton's chemical theory.

The amended hypothesis and the chemical atomic theory.

In the lecture already quoted, Dalton connects this amended hypothesis with the genesis of his chemical atomic theory. " The different sizes of the particles of elastic fluids under like circumstances .... being once established, it became an object to determine the relative sizes and lueigJits together with the relative nnmber of atoms in a given volume. This led the way to the combination of gases .... Thus a train of investigations was laid for determining the nnmber and zveight of all chemical elementary principles which enter into any sort of combination with one another." -'

-' Roscoe and Harden, " New view of the origin of Dalton's Atomic Theory,"

pp. 16-17. -- Phil. Trans., 1826, part 2, p. 174. -" Roscoe and Harden, loc. cil.

Miuic/iesier Meviohs, Vol. Iv. (191 1), No. 5- 15

" This led the way to the combination of gases." Undoubtedly the combination of gases was the basis of Dalton's chemical theory, and the gist of his narrative is, that YiQ first concluded the particles of different gases to be different in size, and subscquoitly arrived at his chemical theory.

iSoj or iSoj ?

Roscoe and Harden, instead of taking this narrative as a document requiring interpretation in the light of the available information, and above all, in the light of Dalton's habit of mind, have accepted it at its face value. Even then they are compelled to admit there is something wrong. The note-books shew that the chemical theory was formed in 1803, and if the amended diffusion hypo- thesis was formed previously, then the date, 1805, which Dalton gives, must be wrong. Roscoe and Harden con- clude that the date of the amended hypothesis is 1803.-*

The date is iSo^, There are two grave objections to the supposition that the theories were formed in the order given by Dalton. One of these is based on the nature of the theories, and will be considered in the next paper. The other has to do with the genesis of the diffusion hypothesis. Roscoe and Harden have failed to quote from the note-book the passage which deals with this. It is as follows : —

" On the iiltimate atoms of elastic fluids.

"There are but three positions that are any way likely to be true on this head.

" I. The ult. atoms of all gases are of the same weight.

2* op. cil,, p. 25.

l6 yiKLD'RXl'M, Deve/opjnent of the A to)inc TJicory.

" 2. The ult. atoms are of the same relative weight as the gases themselves.

" 3. That neither of these positions is accurate.

" According to the first the gases of greatest specific gravity are those whose particles are closest and the diameters of the elastic particles will be as the cube root of the sp. gr. This cannot be true for nit. gas which is made up of azot and oxygen is lighter than oxygen itself ; and so is aq. vapour than oxygen one of its •constituents." ^^

" According to the 2nd position all gases will have the same number of particles, and consequently the same distances of each in a given volume, under like circum- stances. This position is contradicted by facts : for all ■compounds would be heavier than their simples upon this principle, which is contrary to experience.

" The two former positions being disproved, it follows that when two gases of like force, &c., are presented to each other, the number of particles in a given surface of one of them will not be the same as in the other ; conse- quently, no proper equilibrium can take place." -"

This material is as important as anything on the subject can well be. The pages quoted, Nos. 109 and III of the note-book, amount to a summary of Dalton's reasoning on the subject of the sizes of atoms, leading to his decision in favour of the new diffusion hypothesis. It is easy to assign a date to this decision. By reason of the subject-matter, pages 107, 109, and iii are closely con- nected with one another. Page 107 contains a table of the weights and diameters of atoms, a table which, it may well be supposed, was drawn up in order to illustrate X)alton's inquiry into the sizes of atoms. It is dated

-^ Note-books, vol. i, p. 109. '^' Op. cit., p. III.

Manchester Mevioirs, Vol. h. {\gi i), No. 5. 17

September 14th, 1804, and this is the approximate date of the amended diffusion theory.

Dalton probably influenced by Thomson and Gotigh.

Up to this time Dalton had given no sign of anything but the fullest confidence in his original theory. He had defended it eagerly, and, as late as June, had been encouraged in his belief by the accession of William Henry to his side. What then could have induced Dalton, not a very impressionable man, to reconsider the matter ?

It may be assumed, in the absence of any positive information on the subject, that the change was due partly to Thomas Thomson and partly to John Gough. As has already been mentioned more than once in these papers, Thomson visited Manchester with the express object of discussing the mixed gases theory with Dalton. Now everything goes to show that Thomson made a considerable impression on him and won his confidence. He explained the chemical theory to Thomson in detail, and afterwards mentioned Thomson's opinions regarding mixed gases, although adverse to his own, with the utmost respect.-^ Consequently one can well believe that Thomson's scepticism regarding the original mixed gases theory began to shake his confidence in it. Again, John Gough had written two letters, which appeared in Nicholson's Journal^ criticising the theory. The criticism was effective, for Dalton, although he continued to main- tain his theory, made no answer at the time to Gough's argument regarding the velocity of sound. Gough's letters are dated July i6th and August 23rd, 1804, respectively. The interview between Dalton and Thomson occurred on ■-" "New System of Chemical Philosophy," 1808, p. 72.

1 8 Meldrum, Development of the Atomic Theory.

the 27th August, and Dalton's reply to Gough is dated 8th September. Thus Thomson's objections to the theory, with Gough's in addition, may have compelled Dalton to reconsider the matter. There was time for reconsideration between the 8th September and the 14th, the date of Dalton's decision to put the explanation of the diffusion of gases on a new basis.

The principal references connected ivitJi the theory of mixed gases,

1792.

1. "On Evaporation," by Jean Andre Deluc. Phil. Trans.,.

p. 400.

1793-

2. " jMeteorological Observations and Essays," by John

Dalton.

1799.

3. " Experiments and Observations, to determine whether the

quantity of Rain and Dew is equal to the quantity of Water carried off by the rivers and raised by evaporation ; with an Inquiry into the Origin of Springs," by John Dalton. Read* March ist. Vwh. Manchester AlemoirSy vol. 5, part 2, p. 346, 1802. (The footnote, p. 351, was added after the paper was read.)

1800.

4. " Experimental Essays, to determine the Expansion of

Gases by Heat, and the maximum of Steam or Aqueous Vapour, which any Gas of a given temperature can admit of; with observations on the common and improved Steam Engines," by John Dalton. Read April i8th. Never published in full ; see no. 8.

* In ihe above list, " read '" means read before the Manchester Literary and Philosophical Society.

Manchester Memoirs, Vol. Iv. (191 1), No. 5. 19

1801. 5. " New theory of the constitution of mixed aeriform fluids, and particularly of the atmosphere," by John Dalton. Written September 14th. Pub. Nicholson' s Jour., [i], vol. 5, p. 241. 6-g. " Experimental Essays on the Constitution of mixed gases ; on the force of steam or vapour from water and other liquids in different temperatures, both in a torricellian vacuum and in air ; on evaporation ; and on the expansion of gases by heat," by John Dalton. The ist of these four essays was read Oct. 2nd, the 2nd Oct. i6th, the 3rd Oct. 30th. Pub. Manchester Memoirs, [r], vol. 5, p. 535, 1802.

1802.

10. "System of Chemistry," by Thomas Thomson, ist ed.,

vol. 3, p. 270.

11. "New theory of the constitution of mixed gases eluci-

dated," by John Dalton. Written Nov. 18th. Pub. Nicholsoiis Jour., [2 J, vol. 3, p. 267. (Chiefly called forth by no. 10.)

12. "Experimental Inquiry into the Proportion of the several

gases or elastic fluids constituting the atmosphere," by John Dalton. Read Nov. 12th. Pub. Manchester Memoirs, [2], vol. i, p. 244, 1805.

1803.

13. "EssaideChimieStatique,"byC. L. Berthollet (especially

§§ 158, 160, 163, 164, 171, 240, 242—244).

14. "On the tendency of elastic fluids to diffusion through

each other," by John Dalton. Read Jan. 28th. Pub. Manchester Memoirs, [2], vol. i, p. 259, 1805.

15. "On the absorption of gases by water and other liquids,"

by John Dalton. Read Oct. 21st. Pub. Manchester Memoirs, [2], vol. i, p. 271, 1805.

20 Meldrum, Developmetit of the Atomic Theory.

1 6. "An Essay on the theory of mixed gases and the state of

water in the atmosphere," by John Gough. Read Nov. 4th. Pub. Manchester Memoirs, [2], vol. i, p. 296, 1805.

17. "A reply to Mr. Dalton's objections to a late theory of

mixed gases," by John Gough. Written Dec. 2nd. Read Jan. 27th, 1804. Pub. Manchester Memoirs, [2], vol. I, p. 405, 1805.

i8. "Appendix to Mr. William Henry's paper, on the quantity of gases absorbed by water, at different temperatures, and under different pressures." Phil. Trans., p. 274.

1804.

19. "System of Chemistry," by Thomas Thomson, 2nd ed.,

vol. 3, p. 316.

20. "On the supposed chemical affinity of the elements of

common air; with remarks on Dr. Thomson's observa- tions on that subject," by John Dalton. Written June 1 6th. Pub. Nicholson's Jour., [2], vol. 8, p. 145. (A reply chiefly to no. 19.)

21. "Illustration of Mr. Dalton's theory of the constitution of

mixed gases," in a letter from Mr. Wm. Henry, of Man- chester, to Mr. Dalton. Written June 20th, read June 29th. Pub. Nicholson's Joicr., [2], vol. 8, p. 297.

22. "On the solution of water in the atmosphere, and on the

nature of atmospherical air," by John Gough. Written July 1 6th. Pub. Nicholson' s Jour., [2], vol. 8, p. 243.

23. " Strictures on Mr. Dalton's doctrine of mixed gases, and

an answer to Mr. Henry's defence of the same," by John Gough. Written Aug. 23rd. Pub. Nicholson' s Jour., [2], vol. 9, p. 52. (A reply to nos. 20 and 21.)

24. " Observations on Mr. Gough's strictures on the doctrines

of mixed gases, &c.," by John Dalton. Written Sept. 8th. Pub. Nicholson's Jour., [2], vol. 9, p. 89. (A reply to nos. 22 and 23.)

Manchester Memoirs, Vol. Iv. (191 1), No. 5. 21

25. "Atmospherical air not a mechanical mixture of the

oxigenous and azotic gases, demonstrated from the specific gravities of these fluids," by John Gough. ^Vrilten Sept. 5th. Pub. Nicho/sofi's Jour., [2], vol. 9, p. 107.

26. Letter to the Editor from Mr. William Henry in reply to

Mr. Gough. Written Sept. 13th. Pub. Nicholson^ s Jour., [2], vol. 9, p. 126. (In reply to nos. 22 and 23.)

27. " Reply to Mr. Dalton on the constitution of mixed gases,"

by John Gough. Written Oct. i6th. Pub. Nicholsoiis Jour., [2J, vol. 9, p. 160. (A reply to no. 24.)

28. "Observations on Mr. Gough's two letters on ujixed

gases," by John Dalton. Written Nov. 15th. Pub. Nicholson^ s Jour., [2], vol. 9, p. 269 (in reply to nos. 25 and 27).

29. " Further observations on the constitution of mixed gases,"

by John Gough. Written Dec. 13th. Pub. Nicholson's Jour., [2], vol. 10, p. 20, 1805.

1805.

30. " Remarks on Mr. Gough's two Essays on Mixed Gases,

and on Professor Schmidt's experiments on the expan- sion of dry and moist air by heat," by John Dalton. Read Oct. 4th. Pub. Manchester Memoirs, [2], vol. r, p. 425 (a reply to nos. 16 and 17).

1806.

31. "System of Chemistry," by John Murray. Vol. 2, pp. 48-

53, and note E.

1807.

32. "System of Chemistry," by Thomas Thomson. 3rd ed.,

vol. 3, p. 440.

33. "On the Chemical composition of the Atmosphere."

Works, vol. 8, pp. 252-255, by Humphry Davy.

22 Meldrum, Development of the Atoiiiic Theory.

1808.

34. "New System of Chemical Philosophy," by John Dalton,

pp. 150-208.

1809.

35. " Experiments on the expansion of moist air raised to a

boiling temperature," by John Gough. Written May 22nd. Pub. Nicholsoiis Jour.., [2], vol. 23, p 182.

36. " Sur le melange reciprcque des gaz," par C. L. Berthollet.

Mem. cfArceiiit, vol. 2, p. 463 (a repetition of Dalton's experiments in no. 14).

1826.

37. " On the constitution of the Atmosphere," by John Dalton.

Fhil. Irans., part 2, p. 174.

1837-

38. " Sequel to an Essay on the constitution of the Atmosphere,"

by John Dalton. Phil. Trans., p. 347.

1834.

39. Dr. Prout's reply to Dr. W. Charles Henry. Written July

iSth. Phil. Mag., [3], vol 5, p. 133.

1844.

40. " Observations on the Diffusion of Gases," by T. S.

Thomson. Phil Mag., [3], vol. 25, p. 51.

1842.

41. "Elements of Chemistry," by Thomas Graham, pp. 69,

70. 71, 75-

Manchester Memoirs, Vol. Iv. (191 0. ^^0. 0.

VI. The Development of the Atomic Theory : (5) Dalton's Chemical Theory.

By Andrew Nor^ian Meldrum, D.Sc.

( Carnegie A'esearr/i Fclloiv. )

(Commiiiikated by Prof. H. B. Dixon, M.A., F.R.S.)

Received October, igio. Read January 2^th. igi i.

Introduction.

In the year 1801 Dalton's physical atomic theory (described in the fourth paper of this series) was devised as an explanation of the diffusion of gases. Since the pre- vailing tendency of the time had been to regard diffusion as due to chemical affinity between the gases concerned, Dalton was forced to consider carefully the nature of physical and chemical changes, and to draw a distinction between them. His own theory of diffusion turned on this distinction. Thus, in the course of his argument against the supposition that diffusion is due to chemical affinity, he asks the question, " Why do not oxygenous and azotic gases, taken in due proportion and mixed, constitute nitric acid gas, another elastic fluid, totally distinct in its properties, from either of the ingredients."^ Obviously, therefore, whilst Dalton's attention was being d\rec\.&d principally to physical phenomena, he had in his mind a distinct conception of chemical change.

The object of this paper is to consider how Dalton passed from the physical atomic theory, which was formed first, to the chemical one, which was formed afterwards. The author has already shown, in the second paper of this series, that the various narratives we possess of the origin of the chemical theory, can be traced back to

^ Manchester Memoirs, vol. 5, pp. 538-539, 1802. March ytli, igii.

Meldrum, Developmoit of tJic Atomic Theory,

Dalton himself. This is simply what was to be expected in the nature of the case. Moreover, since Dalton was inconsistent in the matter, no single account of his can be accepted at its face value. The version of the origin which is advanced in this paper, consequently, need not be rejected off-hand, as not having received the sanction of Dalton. It is offered as a fair account of the present state of our knowledge, on a matter on which absolute certainty is not yet attainable.

The paper is divided into two parts : — I. The princi- ples of Dalton's theory ; II. The genesis of the theory.

I. The principles of Dalton's theory.

Hie first table of atomic weights.

For the present purpose of studying the origin of the chemical theory, Dalton's note-books contain material of inestimable value : they afford facts which cannot be disputed. Under date 6th September, 1S03, there is an atomic weight table of the highest interest. It is quoted by Roscoe and Harden as follows : — *

Ult. at. hydrogen ... ... i

» » oxygen 566

„ » azote 4

„ „ carbon 4-5

„ „ water ... ... 6 66

„ „ ammonia ... ... 5

„ „ nitrous gas... ... 966

„ „ „ oxide ... 1366

„ „ nitric acid ... ... 1 5'32

„ „ sulphur ... ... 17

„ „ sulphurous acid ... 2266 „ „ sulphuric „ ... 2832 „ „ carbonic „ ... 158

,, „ oxide of carbon ... 102 * " New View of the Origin of Dalton's Atomic Theory," p. 28.

. Manchester Memoirs, Vol. Iv. (191 1), No. 45. 3

This table of atomic weights is of extraordinary interest because, besides being the earliest known, it is based on the same ideas as the one published in the " New System '' five years later. There is only one change : sulphurous and sulphuric acids in the earlier table are virtually SO and SOj respectively, and in the later table they are SO. and SO.,. But this does not affect the fact that after the table was drawn up in 1803, Dalton made no essential change in the theory. The principles of 1S03 remain as nearly as possible unchanged in 1808, so far as one can judge of principles by results. In the one scheme just as in the other, the compound atom of water consists of I atom of hydrogen and i of oxygen, that of ammonia of i of hydrogen and i of nitrogen. Nitrous gas is virtually NO, nitric acid is NO., nitrous oxide N.O, carbonic oxide is CO, carbonic acid is CO2.

Debus on the '' Dalton- Avogadro " hypothesis.

Debus has devoted a series of papers to the study of the principles on which Dalton arrived at chemical formulae and atomic weights. The whole series may be said to depend on the assumption that Dalton deliberately made a mystery of the evolution of his theory. " Der geniale Baumeister hat sorgfaltig alle Werkzeuge und Plane entfernt und zeigt ohne einleitende Bemerkungen sofort das fertige Gebaude." - This is the kind of state- ment which ought not to be made except as the result of an exhaustive study of the available material. Everyone must admit that the subject is obscure, but, as will appear in the course of this paper, there is little justification for saying that Dalton deliberately (sorgfaltig) made it so. The true explanation of the obscurity is that the task of

- Zeitsch. pliysik. Chan., 1899, vol. 29, p. 266.

4 Meldkum, Development of t lie Atomic Theory.

considering how his own ideas had arisen was uncongenial to him, and he never devoted his mind to it.

As the result of his studies, Debus conckided that Dalton was greatly influenced, during the development of his atomic theory, by the supposition that the particles of different gases under similar conditions are of the same size. This doctrine, which is usually known as Avog- adro's hypothesis, Debus calls the " Dalton -Avogadro" hypothesis.

Debus first advanced this belief of his in a pamphlet entitled, " Ueber einige Fundamentalsatze der Chemie, insbesondere das Dalton-Avogadrosche Gesetz " (1894, Cassel). His opinion having been controverted by Roscoe and Harden, in their " New View of the Origin of Dalton's Atomic Theory," he replied, and a controversy ensued, in which G. W. A. Kahlbaum also took part. The series of papers is as follows : — Debus, Zeitsch. physikal. Cliem., vol. 20, p. 359, 1896 (or PJiil. Mag., vol. 42, p. 350, 1896); Roscoe and Harden, Zeitsch. physikal. Chem., vol. 22, p. 241, 1897 (or Phil. Mag., vol. 43, p. 153, 1897); Debus, Zeitsch. physikal. Chem..,. vol. 24, p. 325, 1897; vol. 29, p. 266, 1899; Kahlbaum, Zeitsch. physikal. Chem., vol. 29, p. 700, 1899; Debus, Zeitsch. physikal Chem., vol. 30, p. 556, 1899.

Debus can justify his belief in two ways : — (i) Dalton certainly stated in 1808 that he once had a sort of belief in the hypothesis in question. " At the time I formed the theory of mixed gases, I had a confused idea, as many have, I suppose at this time, that the particles of elastic fluids are all of the same size ; that a given volume of oxygenous gas contains just as many particles as the same volume of hydrogenous ; or if not, that we have no. data from which the question could be solved. But ....

Manchester Mcuioirs, Vol. h. (191 1), No. 0. 5

I became convinced that different gases have not their particles of the same size." '

(2) Debus argues, from a phrase in Thomas Thomson's first sketch of the atomic theory, that Dalton was still in 1804 a believer in the hypothesis. This is the phrase, ^' the density of the atoms."

The ''density of the atoms'^

The interpretation of this phrase is open to questionj and Roscoe and Harden do not agree with Debus on the matter. But neither they nor any of the parties to the controversy seem to be aware that Dalton put exactly the same construction on the phrase as Debus, and at the same time repudiated the opinion which it attributed to him. " It is rather amusing to me to observe the different manners in which a cursory view of the atomic system strikes different observers. Dr. Thomson . . , used the phrase density of the atoms indifferently for iveight of the nionis, thereby implying that all atoms are of the same size, and differ only in density ; but he has since very properly discontinued the use of the phrase."^

It is, of course, impossible that a statement, made by Dalton in 18 14, can be taken to prove that he did not use a misleading expression in a conversation held ten years earlier. He may have used the phrase in question in his interview with Thomson, or Thomson may have originated the phrase. These are the two possibilities. But the matter is not one of high importance. There are far stronger arguments than this statement of the year 1 8 14 can be, against the opinion held by Debus.

" "New System of Chemical I'hilo.soijhy," iSoS, pp. 187-1S8. * Ann. of Phil., vol. 3, p. 175, 1814.

6 MeldrUM, Development of tJic Atomic TJicory.

Dalton practically ignores the hypothesis.

The really important question is, the sense in which Dalton held this hypothesis. Did he perceive and con- sider all its consequences, immediate and remote, and did he, in any \va\', act upon his belief in it ? That he did none of these things is the plain meaning of the passage in which he speaks of his holding the hypothesis as a "confused idea."

There are four different ways in which Dalton might have applied the hypothesis, or drawn deductions from it :

1. The hypothesis is to the effect that particles of nitrogen and ox\-gen are of the same size. Dalton's first explanation of diffusion was that particles of oxygen neither attract nor repel those of nitrogen. Between these two opinions there is no necessary connection. He did not hold the diffusion theory as a logical consequence of the hypothesis, and he did not even specify the hypo- thesis in his explanation of the theory.

2. Dalton did not use the hypothesis as a means of arriving at atomic weights and formula;. He used for that purpose the i : i rule, which led him to the formula OH for water, whilst the hypothesis must have led to the formula H.^O. Thomson, in his first sketch of the theory, says expressly that the i : i rule was " the hypothesis on which the whole of Mr. Dalton's notions ... is founded."^

3. What is known as Gay-Lussac's law, regarding the combining volumes of gases, is a necessary con- sequence of the hypothesis. This everyone must admit. Yet Dalton did not at once deduce the law from the hypothesis, and when at length he did so, and endeavoured to test it experimentally, he regarded his results as dis-

'' " S}'stem of Chemistry,'' 31x1 edition, 1S07, vol. 3, p. 424.

AlcuicJicster hfenioirs, J^o/. h: (igii), No. ^. 7

province both doctrines. Debus, as the author has pointed out elsewhere, has committed himself to the opinion that Dalton could be at one and the same time a believer in the hypothesis and not in the law.''

4. Finally, Dalton held this hypothesis without con- sidering that it leads to the conclusion, familiar now to chemists, that the " atoms " of hydrogen, oxygen and other elements are divisible.

There is no evidence, not the faintest indication, that Dalton had realised the hypothesis before the end of the year 1803, ^^ ^^W o"g of these four ways. It is, therefore, impossible to suppose that the hypothesis — the "confused idea" — had any influence on him whilst he was forming his chemical atomic theory,

T/ie main principles of Daltuiis system.

The principles on which Dalton based his theory must have continued the same from 1803 to 1808, simply because his opinions regarding the " atom " of water, of ammonia, etc., remained the same. The general prin- ciples regarding the combination of atoms, which he set out in 1808, are somewhat cumbrous, and some of them superfluous. They can be reduced to two: — (i) That atoms of different kinds tend to combine in the propor- tion I : I rather than in any other, that the next propor- tion to occur is I : 2, then i : 3, and so on ; (2) that when two compounds of the same two elements are gaseous, the lighter is binary and the heavier tertiary.

It is true that this second principle is not to be found among the set of rules which Dalton gives in the " New System of Chemical Philosophy." He says there that

« " Avogadro and Dalton — the standing in Chemistry of their hypotheses," 1904, pp. 63-66.

8 Meldrum, Deuclopuient of the Atomic Tlieoty.

"a binary compound should always be specifically heavier than the mere mixture of its two ingredients " [compounds and ingredients being supposed to be gaseous]. This rule is open to two objections : — (i) It is not true, as the case of hydrochloric acid shows ; (2) it is of no use and was not used for the problem that Dalton had to solve. It cannot be used to ascertain whether the two gaseous oxides of carbon ought to receive the formula CO and CO2 respectively, or CoO and CO. In the 2nd part of the " New System " he says : — " carbonic acid is of greater specific gravity than carbonic oxide, and on that account it may be presumed to be the ternary or more complex element \^sic\. It must, however, be allowed that this circumstance is rather an indication than a proof of the fact." ' One can well believe that it was on this principle Dalton arrived at the molecular constitution of these gases, and of nitric and nitrous oxides as well, in the year 1803.

The connection between the physical and the chemical theories.

The first rule has been called the rule of " greatest simplicity," not only in allusion to its character, but as meaning that it is based on the instinct for simplicity and needs no other justification. As a matter of fact Dalton deduced it from first principles. Dr. Bostock, in the course of a criticism of the atomic theory, raised the question, " When bodies unite only in one proportion, whence do we learn that the combination must be binary?"

In answer Dalton gave an explanation, which shows that Newton's postulate of similar particles, which are *' mutually repulsive," was the fundamental idea of the

"^ "New System ofCliemical Philosophy,"' iSiO, p. 369.

Manchester HTcvioirs, Vo/. h. (191 1), No, 4>. 9

chemical as it had been of the physical atomic theory. ^' When an element A has an affinity for another B, I see no mechanical reason why it should not take as many atoms of B as are presented to it, and can possibly come into contact with it, . . . except in so far as the repulsion of the atoms of B among themselves are \sic\ more than a match for the attraction of an atom of A. Now this repulsion begins with 2 atoms of B to i of A, in which case the 2 atoms of B are diametrically opposed ; it increases with 3 atoms of B to i of A, in which case the atoms of B are only 120° asunder .... and so on in proportion to the number of atoms. It is evident then from these positions, that, as far as powers of attraction and repulsion are concerned (and we know of no other in chemistry) . . . binary compounds must first be formed in the ordinary course of things, then ternary and so on, till the repulsion of the atoms of B . . . refuse to admit any more.""

Consequently, Newton's postulate of similar particles which are mutually repulsive, is the basis of both the physical and the chemical atomic theories of Dalton.

II. The genesis of the ciie^mical theory. The inductive and deductive accounts of the genesis.

This discussion of principles, however, does not exhaust the subject. Much remains obscure regarding the train of thought which Dalton followed in passing from the physical to the chemical theory. The crucial question is, how he arrived at, what suggested, the doctrine of combination of atoms in multiple proportion?

Two main accounts of the origin of the theory have

'^ Nicholson'' s Join ., vol. 29, p. 147, iSii ; see also '' New System of Chemical Philosophy," vol. i, p. 216, iSoS.

lo Mkldrum, DevelopJiient of the Atomic Theory.

been offered. They have already been mentioned in the second paper of this series. The first of these, coming direct from Thomas Thomson, is that Dalton discovered the composition of marsh gas and olefiant gas and was led thereupon to perceive the law of multiple proportions, and to devise his chemical theory as an explanation of the law. This may be called the inductive account.

Again, Roscoe and Harden accept an account, offered by Dalton, which may be called the deductive one. Dalton had formed his diffusion hypothesis without considering the " effect of difference of size in the particles of elastic fluids." On consideration he found that " the sizes must be different," and thereupon he revised his diffusion theory. He then introduces the subject of the chemical theory : — " The different si::es of the particles of elastic fluids .... being once established, it became an object to determine the relative si.zes and weights, together with the relative number of atoms in a given volume. This led the way to the combination of gases," etc.

Objections to the purely inductive and ded^ictive accounts.

There being these two accounts, the inductive one and the deductive, of the origin of the theory, there arises the question, which comes nearer the truth? The Board of Education has recently committed itself to an opinion on this topic, in the course of its criticisms on the answers of students to its questions on chemistry. The particular question was : — " Give a short account of Dalton's atomic theory, and discuss its value in explaining the laws of chemical combination."

Teachers of chemistry, to judge from the reference made to them, have been adopting Roscoe and

MancJiester Memoirs, Vol. Iv. (191 1), No. <>. ir

Harden's view of the matter. "... The teachers are to blame ... in allowing so many of their students to put the " cart before the horse" as they do in connection with the atomic theory. The idea seems to prevail that the laws of chemical combination follow from the atomic theory, whereas the laws of combination were established first as the results of experiments, and the atomic theory of Dalton provides an explanation of the facts.""

It is, of course, begging the question to assume that the matter is as simple as this. Everyone knows which is the cart and which is the horse, and no one knows for certain how Dalton's chemical theory arose. Again, one may urge, that supposing the origin of the theory to be a controversial matter, the Board of Education is not called upon to take one side or the other, and indeed,, might well avoid such topics in its examination papers.

The matter, however, is no longer controversial, being so far settled that the purely inductive view of the origin is quite untenable. There is the objection to it in prin- ciple, that it says nothing about Dalton's physical theory to which W. C. Henry drew attention long ago, and Roscoe and Harden recently. Besides, Roscoe and Harden have advanced objections to it in detail, which must be final to anyone who considers them.^"

Reasons must now be offered for rejecting the deductive account which Roscoe and Harden have accepted. The gist of it is that Ualton fi^st satisfied himself that the atoms of different gases have different sizes, and then devised the chemical theor}\ This, Dalton's own narrative, has already been quoted on p. 10. He gave it seven years after the events which it relates, and it is quite unsatisfactory. It does not condescend to

" " Science Examinations," 1909, p. 119. Board of Education. ^ " " New View of the Origin of Dalton's Atomic Theory,"' p. 2S.

12 MeldrUM, DevelopDient of the Atomic Theory.

particulars and instances, Dalton does not explain, nor is it obvious that anyone can explain, how he was to test the sizes of atoms without some kind of chemical theory. One may either assume that different atoms have the same size, and act accordingly, or one can endeavour to test the position, by obtaining data regard- ing atoms, on the basis of some hypothesis as to the way in which they combine chemically.

It has been shown in this paper that Dalton, so far as the formation of the chemical theory is concerned, did not act on the belief that atoms of different kinds have the same size. Again, the author has already shown, in the paper on Dalton's physical atomic theory, that the chemical theory was formed first and the conclusion that "atoms" of different gases were different in size was come to afterwards.

This is the order that was to be expected in the nature of the case. Moreover, there is nothing in the note-books to show that the chemical theory was devised except for its own sake. The testing of the sizes of atoms was an afterthought. The connection between the sizes of atoms and the diffusion of gases was not con- sidered till a year after the chemical theory had been formed.

The cxperiuieiits of August ^th, i8oj.

The chief matter that continues to be doubtful is the exact way in which Dalton arrived at the law of multiple proportion. The author, after a careful consideration of the evidence, can come to no other conclusion than that it was Dalton's experiments on the combination of nitric oxide and oxygen that aroused his attention, and made him apply his physical theory to the purposes of chemistry.

Manchester Memoiis, J\>/. Iv. (191 1), No. 0. 15.

The facts, as established by the note-books, are that Dalton, for the purpose of his inquiry into the composition of the atmosphere, was studying the combination of nitric oxide and oxygen in the year 1803. He was at work on the subject during March and April, and then again in August. On the 4th of August he obtained the well- known result that 100 measures of air could take 36, or 72, of nitric oxide.^' His first table of atomic weights was drawn up by the 6th of September.

The first case of combination in multiple proportions observ^ed by Dalton must have seemed of great importance to him. His observation of August 4th, regarding nitric oxide and the oxygen of the air, is the first of the kind which he recorded. It is difficult to suppose that he can have known an earlier one. Yet Roscoe and Harden think that this case was of comparative unimportance in the development of the atomic theory. Their reason is that the chemical compounds concerned are not sufficiently represented in the first table of atomic weights. The chemical changes, as Dalton understood them, may be set out in the equations : —

(i) NO + 0-=NO., (nitric acid). (2) 2N0 + 0 = NA ("'trous „ ).

Certainly, if the whole matter turned on nitrous acid, Roscoe and Harden argue, it is surprising that Dalton ignored this substance in making up his table on September 6th. They suggest that the symbol for nitrous acid which appears at the side of the table was added after- wards, probably about the 12th October. Everyone must admit this who inspects the original table, or the photo- graph in Roscoe and Harden 's book.

Dalton seems to have set aside the case of nitrous acid

^1 Roscoe and Harden, op. ciL, pp. 34, 38.

14 MELDRU^r, Development of the Atomic Theory.

for a time as being too complicated. The union of two atoms of one kind with three of another must have appeared at that stage of thought to be very complex. Dalton did not adopt such a formula till October. On the 1 2th of that month, as a summary of his views, he gives tables of binary compounds, of ternary, of compounds of 4 atoms, and compounds of 5. Alcohol and nitrous acids were the only compounds of 5 atoms. Alcohol is ether and water united, or 2 oxygen, 2 carbon, and i hydrogen. Nitrous acid is 3 oxygen and 2 nitrogen.

The objection of Roscoe and Harden, however, must 'be final, but for one circumstance : the objection ignores the physical theory. The experiments with nitric oxide ■and air must have received lengthy consideration had it not been for the fact that Dalton had an atomic theory already in his mind. As it was, these experiments simply served to give the impulse needed to set his mind working. Under that stimulus he ma.de a beginning with the adaptation of the physical theory to chemical purposes.

Nothing more was needed. Larmor, in his Wilde Lecture on the " Physical Aspect of the Atomic Theory," represents that the doctrine of combination of atoms in the proportion i : i must forthwith lead to other cases such as I : 2.

" Once it is postulated that only one kind of aggrega- tion into molecules occurs, e.g.., that in water there is only one way in which the hydrogen attaches itself to the ■oxygen, the laws of definite and multiple proportions are self-evident."'"

Earlier in this paper, the author has pointed out how the doctrine of i : 1 arose logically from the physical theory. There are here, therefore, all the elements of a fair account of the origin of Dalton's chemical theory.

^^ Manchester Memoirs, vol. 52, no. 10, p. 9. 1908.

MaiicJiestcr Memoirs^ Vol. h. (191 1), iV^^. <». 15

The germ of it is to be found in Newton's theory and in Dalton's physical theory of the year 1801, and one must recog;nise the space of two years during which it remained in the germ. There comes tlien the experiment of the 4th of August, 1803, sufficient to arouse Dalton's attention and make him apply his theory to the purposes of chemistry. He frames the rule of i : i, then considers the less simple cases, and tests his ideas by the available analytical data. By the 6th of September he is able to draw up the first atomic-weight table.

Clieuiistry tvithout the atomic tJieory.

Attempts have been made in recent years, by VVald and Ostwald, to deduce the laws of chemical combination from first principles, without making any use of the atomic theory.'" It seems to the author worth pointing out here that there is no connection between the modes of thought taken by these writers, and the process by which these laws were actually established. With the atomic theory as a starting point, they were formulated by Dalton and completely established by Berzelius. Moreover, at the same time and as a matter of course, the foundations •of chemical analysis as a genuine science were laid.

The failure of other icorkcrs.

Sufficient attention has not been given to the question, why it should have been left to Dalton to draw attention to the law of multiple proportion ? It was not the want of interest in the subject of chemical composition. The workers on the subject, towards the end of the eighteenth and the beginning of the nineteenth century, were quite numerous. One may name Bergman, Wenzel, Klaproth, Lavoisier, Richter, Kirwan, Thomson, Bucholz, Chenevix,

^^ See the Faraday Lecture, Trans. Clieui. Soc, 1904.

i6 Meldkum, L)evelopmc7it of tJic Atomic Theory.

Bostock, Clement, Dtisormes and Proust. Yet the failure of these chemists to discover the law of multiple propor- tion, despite their immense labours, was complete.

An incorrect expla}iatio II of the failure.

The reason usually offered for this failure is, that the- data for the composition of substances were calculated in such a way as to hide the law.'* Plainly the implication is, that the data calculated in a suitable way must reveal the law at once. This is mere guess-work, for as a matter of fact, data were frequently stated in precisely the way required. Proust, for instance, gives practically all his data for the oxides and sulphides of a metal, in terms of lOO parts of the metal. ^'

The true explanation.

The true explanation is twofold. In the first place, accurate chemical analysis is impossible without a check of some kind. That the analyst should have good intentions, even the best intentions, is not enough. In the absence of a guiding principle, chemists cannot tell when a substance is pure, or when an analysis is correct. As explained in the first paper of this series, it was this state of uncertainty which contributed at the beginning of the nineteenth century, more than anything else, to the spread of C. L. Berthollet's ideas regarding combination in indefinite proportions. Arrhenius has pointed out that every chemist noiv prepares his substances so that

^* E. von Meyer, "Hist, of Cliem.,"' Eng. trans., pp. 195-196, 1906, and Arrhenius, "Theories of Chem.,"' Eng. trans., p. 16, 1907.

15 Ann. de Chitii., vol. 28, p, 214, 1798 ; Jour, de P/iys.^ vol. 54, p. 92, 1802 ; vol. 55, p. 330 ; vol. 59, p. 324, 326, 330, 352, 1804 ; vol. 62, p. 136^ 138, 139, 1806 : vol. 63, p. 431, 1806.

Manchester Memoirs, Vol. iv. ( 1 9 1 1 ), No. 0. 1 7

they agree with the laws of definite and multiple pro- portions.

In the second place Dalton was at an advantage over other workers, in having a theory to which he could refer facts. Something more is needed than important facts, one must have the eye to perceive their importance. Charles Darwin gives an illustration of this when he admits he once walked along a valley, full of the plainest indications of glacial action which he absolutely failed to notice. " On this tour I had a striking instance how easy it is to overlook phenomena, however conspicuous, before they have been observed by anyone. We spent many hours in Cwm Idwal, examining all the rocks with extreme care, as Sidgwick was anxious to find fossils in them ; but neither of us saw a trace of the wonderful glacial pheno- mena all around us ; we did not notice the plainly scored rocks, the perched boulders, the lateral and terminal moraines. Yet these phenomena are so conspicuous that, as I declared many years afterwards — a house burnt down by fire did not tell its story more plainly than did this valley." "'

This is not a fanciful argument, but one that can be amply justified by facts. Chemists did not go on making analyses conscientiously without sometimes obtaining data in good agreement with the law of multiple propor- tion. But they quite failed to perceive the significance of the data. Dalton himself was able afterwards triumph- antly to point out more than one such case, which had escaped the notice of the chemist concerned. He quotes Bostock's analyses of the acetate and superacetate of lead :—"<

^" "Life and Letters of Charles Darwin," 3 vols., 1887, vol. i, p. 57. '■'' Nicholson'' s /our., vol. 11, p. 75, 1805 ; vol. 29, p. 150, iSii.

1 8 Meldrum, Development of the Atomic Theory.

Acetate. Superacetate.

Lead lOO loo

Acid 24 49

Again, he gives the instance of the oxides of carbon : "Carbonic oxide contains just half the oxygen that carbonic acid does, which indeed had been determined by Clement and Desormes . . . who, however, had not taken any notice of this remarkable result." '^

^® Roscoe and Harden, op. ciL, p. 117.

Manchester Mejnoirs, Vol. Iv. (191 1), No. 7-

VII. The Behaviour of Bodies floating in a Free or a Forced Vortex.

By Professor A. H. Gibson, D.Sc.

Uimiersity College, Dundee. Received January iitli. igi i. Read Januaiy 24th. iqii.

§ I. To anyone who has watched the behaviour of bodies floating in a vortex, whether of dimensions comparable with that of the whirlpool in the Niagara Gorge or such an one as may be formed in stirring one's tea, and who has noted how some objects are apparently irresistibly drawn into the centre of the vortex, while others revolve around its outer boundary, and others again alternately approach and recede from its centre, it must be apparent that the forces producing these various results must be of considerable complexity.

In a series of experiments recently carried out by the author an attempt has been made to determine how, in either a free or a forced vortex, the behaviour of the object depends upon : —

{a) Its size, the depth of immersion remaining constant.

{b) The linear dimensions, in similar objects of the same specific gravity.

{c) The depth of immersion, in bodies of the same cross sectional area but of different specific gravities.

{d) The position of the centre of gravity in non- homogeneous bodies of the same size and shape.

{e) The shape of the body.

(/") The intensity of the vortex action.

March yth, igii.

2 Gibson, Bodies floating in a Free or a Forced Vortex.

§ 2. Experiments on Free Vortex. The free vortex experiments were carried out in a cylindrical tank, two feet in diameter and one foot deep. This is supplied with water through a pipe iMn. in diameter, making connection with the tank through an external volute whose centre line is six inches above the bottom of the tank, while discharge takes place through a central hole in the bottom of the tank. The intensity of the vortex action was varied by enlarging this hole from one inch in the first series of experiments to ijin. in the second series, and by varying the head of water in the tank from 9 inches to 12 inches. Throughout the experiments the motion approximated very sensibly to that of flow in a true free vortex. The motion, as investigated by colour bands, was steady and non-sinuous, and the surface smooth and free from waves.

In the experiments carried out under a head of nine inches, the form of the surface profile is indicated in the following table.

Radius (ins.)

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6

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3

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Ditto, with \\ inch| orifice ... ...j

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—

The first of these orifices discharges "0109 cub. ft. per second, and the second 0152 cub. ft. per second under this same head.

A series of experiments carried out to determine the value of the coefficient of discharge for each of the orifices

MancJiestcr Mcvioirs, Vol. Iv. (1911), No. 7. 3

under heads varying from 8 to 12 inches, showed this to be sensibly independent of the head, and to have value of '287 in the lin. orifice and '178 in the iMn. orifice. The accompanying tables detail the behaviour of the floating bodies in typical cases of the experiments of each series.

The following appear to be the main conclusions to be drawn from the free vortex experiments.

(a) Floating particles whose dimensions are very small compared with those of the orifice, rotate in spiral paths approaching with a continually increasing velocity, and finally disappearing down the funnel of the vortex. The rate of approach of such particles is sensibly the same as that of the fluid itself. (In the second series of experi- ments such particles, of sawdust, described about 40 revolutions while approaching the centre from 9 inches radius.) The lighter particles, however, show a distinct tendency to approach the centre more rapidly than those of a higher specific gravity.

((^) If of dimensions which are moderate compared with those of the vortex, the behaviour depends largely on the shape, size, weight, and position of the centre of gravity of the object. In every case the latter rotates, about its own axis, relative to the surrounding water, in the opposite direction to that of its revolution around the centre of the vortex. If introduced near the periphery of the vessel it usually approaches the centre, and may either settle down to rotate in seeming equili- brium at some definite radius,alternately approach and recede from the centre, or straightway dis- appear down the funnel.

4 Gibson, Bodies floating in a Free or a Forced Vortex.

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10 Gibson, Bodies floating in a Free or a Forced Vortex.

(i) Where homogeneous bodies have the same specific gravity, depth of immersion, and shape of plane of flotation, generally speaking the larger shows the greater tendency to approach the centre. In bodies, the section of whose plane of flotation approximates to a rectangular form, this appears to be generally true, but in circular cylindrical bodies floating with vertical axes, there appears to be a critical diameter, — from lin, to i|in. in these experiments — for which the repellent effect of the vortex for small radii of revolution is very marked. Objects, whether of a greater or less diameter than this, show a greater tendency to be drawn into the vortex, though this effect is more marked with increasing than with diminish- ing sizes. Cf Experiments A (i to lo) ; B (i to 5) ; C (i to 9). The same applies, in a lesser degree in the case of bodies of square section, but here the critical size appears to be somewhat less. Cf. A (23 to 26) ; C (24 to 28) ; A (27 to 32) ; C (14 to 17). Cylindrical objects of a size somewhat larger than, but approximating to the critical, appear to have a definite circle of rotation on the lip of the funnel, in which, except when affected by ex- traneous circumstances, they may rotate indefinitely. If displaced outwards from this circle they return, while if displaced inwards they are drawn down the funnel. Objects somewhat smaller than the critical size — from •Mn, to lin. diameter — have an equilibrium circle of much greater radius, usually from 7 to 10 inches in these experiments. The radius of the equilibrium circle for a given object increases with the intensity of the vortex. For objects of greater size than the critical, it increases, within limits, with the size of object, the largest object to have an equilibrium circle in these experiments being of three inches diameter.

Manchester Memoirs, Vol. Iv. (191 1), No. 7- n

(2) Where similar homogeneous bodies are of the same specific gravity, the larger tends to approach the centre more rapidly. Cf. A (16 & 17), (8 & 14) ; C (12 & 13).

(3) In bodies of the same shape and size but of different specific gravities the lighter tends to approach the centre more rapidly. Cf A (12 & 16), (18 & 19), (7 & 21), (39 & 40), (46, 47 & 4S) ; C (9 & 10), (30 & 31 j, (34 & 35)-

(4) In non-homogeneous bodies of the same size, shape and weight, the lower the centre of gravity the less is the tendency to approach the centre. With the C.G. sufficiently low down the body gradually works out from the centre of the vortex. Cf A (19 & 20), (40 & 41), (43, 44 & 45); C (10 & II), (31 & 32), (35 & 36;. Com- paring A (21 & 22) it appears that the relative lightness of cylinder 22 more than counterbalances the change in

the relative position of the centre of gravity as compared with cylinder 21.

In homogeneous bodies of the same size and depth of immersion, those more nearly approximating to a circular form of cross section show the lesser tendency to approach the centre, the difference becoming more marked as the size increases. Cf A (i to 6, 27 to 32 & 33 to 38) ; (8 & 23), (12 & 25), (23 & 39) ; C (i to 5, 14 to 17 & 18 to 23) ; (24 & 30); (7 & 24).

In vortices whose intensity is increased by increasing the quantity of water discharged, either by increasing