March 31, 1887] 



NA TURE 



52: 



might have slighted the importance which he attached to the 

 water of salts and the temperature at which it was reduced, but 

 in his hands it was a revelation of some of the most mysterious 

 internal phenomena of these bodies. 



" A chemist must take great pleasure in following Graham 

 when he seeks the laws of the diffusion of liquids and traces their 

 connections, especially when they lead to such results as he ex- 

 pressed by dialysis, a process founded on a new classification of 

 substances, and promising still the most valuable truths. We see 

 in the inquiry how Graham thought on the internal constitution 

 of bodies, by examining the motion of the parts, and from the 

 most unpromising and hopeless masses under the chemist's 

 hands — amorphous precipitates of alumina or of albumen — 

 brought out analogies which connected them with the most in- 

 teresting phenomena of organic life. Never has a less brilliant 

 lo:iking series of experiments been made by a chemist, whilst 

 few have been so brilliant in their results or promise more to the 

 inquirer who follows into the wide region opened." 



In a short paper entitled "Speculative Ideas respecting the 

 Constitution of Matter," originally published in the Proceedings 

 of the Royal Society for 1863, Graham has left us his Confession 

 of Faith upon the subjects to which he had devoted the whole of 

 a thoughtful life. He conceives that the various kinds of 

 matter now recognised as different elementary substances may 

 possess one and the same ultimate or atomic molecule existing in 

 different conditions of movement. Graham traces the harmony 

 of this hypothesis of the essential unity of matter with the equal 

 action of gravity upon all bodies. He recognises that the 

 numerous and varying properties of the solid and liquid, no less 

 than the few grand and simple features of the gas, may all be 

 dependent upon atomic and molecular mobility. Let us 

 imagine, he says, one kind of substance only to exist — p inder- 

 able matter ; and further that matter is divisible into ultimate 

 atoms, uniform in size and weight : we shall have one substance 

 and a common atom. With the atom at rest the uniformity of 

 matter would be perfect. But the atom possesses always more 

 or less motion, due, it must be a.ssumed, to a primordial impulse. 

 This motion gives rise to volume. The more rapid the move- 

 ment the greater the space occupied by the atom, somewhat as 

 the orbit of a planet widens with the degree of projectile velocity. 

 Matter is thus made to difter only in being lighter or denser 

 matter. The specific motion of an atom being inalienable, light 

 matter is no longer convertible into heavy matter. In short, 

 matter of different density forms different substances — different 

 inconvertible elements as they have been considered. 



It should be said that Graham uses the terms "atom" and 

 "molecule" in a wider sense than that which the limitations of 

 modern chemistry have imposed upon them, and that he is 

 referring to a lower order of molecules or atoms than those 

 which more immediately relate to gaseous volume. The com- 

 bining atoms of which he conceives the existence are not the 

 molecules of which the movement is sensibly affected by heat 

 with gaseous expansion as the result. Accjrding to Graham, the 

 gaseous molecule must itself be viewed as composed of a group 

 or system of the inferior atoms, following as a unit laws similar to 

 those which regulate its constituent atoms. He is in fact apply- 

 ing to the lower order of atoms ideas suggested by the gaseous 

 molecule, just as views derived from the solar system are extended 

 to the subordinate system of a planet and its satellites. 



We cannot as yet fix any limit to this process of molecular 

 division. To Graham the gaseous molecule is a reproduction of 

 the inferior atom on a higher scale. The diffusive molecules, 

 the molecules or systems which are affected by heat, are to be 

 supposed uniform in weight but to vary in velocity of movement 

 in correspondence with their constituent atoms. Hence the 

 molecular volumes of different elementary substances have the 

 same relati m to each other as the subordinate atomic volumes of 

 the same substances. 



On this basis Graham builds up a conceptioa of chemical com- 

 bination. He points out, in the first place, that these more and 

 less mobile or light and heavy forms of matter have a singular 

 relation connected with equality of volume. Equal volumes of 

 two of them can coalesce together, unite their movement and 

 form a new atomic group, retaining the whole, the h.alf, or 

 some simple proportion of the original movement and consequent 

 volume. 



Chemical combination thus becomes directly an affair of 

 volume and is only indirectly connected with weight. Combin- 

 ing weights are different because the densities, atomic and 

 molecular, are different. The volume of combination is uniform, 



but the fluids measured vary in density. This fi.xed combining 

 measure — Graham's iiiclron of simple substances — weighs i for 

 hydrogen, 16 for oxygen, and so on with the other "elements." 



Graham, however, points out that the hypothesis admits of 

 another expression. Just as in the theory of light we have had 

 the alternative hyp itheses of emission and undulation, so in 

 molecular mobility the motion maybe assumed to reside either in 

 separ.ate atoms and molecules, or in a fluid medium caused to undu- 

 late. A special rate of vibration or pulsation originally imparted 

 to a portion of the fluid medium enlivens that portion of matter 

 with an individual existence, and constitutes it a distinct element 

 or substance. 



The idea of the essential unity of matter finds its analogy, to 

 Graham's thinking, in the continuity of the so-called physical 

 states of matter. He clearly perceived that there is no real 

 incompatibility in the different slates of gas, liquid, and solid. 

 These physical conditions are, indeed, often found together in the 

 same substance. The liquid and the solid conditions supervene, 

 as Graham puts it, upon the gaseous condition rather than 

 supersede it. They do not appear as the extinction or suppres- 

 sion of the gaseous condition, but as something superadded to 

 that condition. Graham conceives that the three conditions (or 

 constitutions) probably always co-exist in every liquid or solid 

 substance, but one predominates over the others, just as the 

 colloidal condition or constitution which intervenes between the 

 liquid and crystalline states extends into both, and probably 

 affects all kinds of solid and liquid matter in a greater or less 

 degree. Hence, to Graham's thinking, the predominance of a 

 certain physical state in a substance appears to be a distinction 

 analogous to those distinctions in natural history which are pro- 

 duced by unequal development. Liquefaction or solidificition 

 does not involve the suppression of the atomic or molecular 

 movement but only the restriction of its range. 



Such then are Graham's ideas, formulated in 1863, respecting 

 the probable constitution of matter. I have purposely stated theuv 

 in great detail, and for the most part in Graham's own words. 

 The paper is very short, but it has evidently been put together 

 with great care. It is impossible not to be struck with the 

 evidence it affords of Graham's insight, his grasp of principles 

 and power of co-ordination. Consider, for example, what 

 he says respecting the continuity of the so-called physical 

 states of matter, and bear in mind upon what an extremely 

 small experimental basis it rested at that time. The obser- 

 vations of Caignard Latour were almo t forgotten, or at all 

 events their significance was not understood. The classical 

 work of Andrews was not yet published. And yet this work and 

 that of a dozen experimentalists in France, Ru-sia, and Germany, 

 has only served to confirm and expand Graham's fundamental 

 conception. The whole paper shows Graham in a very different 

 light from that in which the student of to-day might be apt to 

 regard him. The greater number of his memoirs are mainly the 

 records of measurements, but Graham was not a great measurer 

 in the sense in which we apply that term to such men as 

 Regnault, Magnus, or Bunsen. Very little of his work was done 

 by his own hands, and it must be confe^sed that the earlier 

 experimental portion was occasionally intrusted to apparently 

 inexperienced assistants. Graham had, however, ihe foi sc/icr- 

 blick which characterises the true investigator, and he possessed 

 a really marvellous faculty of sifting out the small grain of fact 

 which often lay hidden beneath a mass of imperfect observation. 

 And yet he was in no hurry to theorise. He patiently added 

 fact to fact, repeating and verifying his observations long after 

 he had got an inkling of the truth towards which they were tend- 

 ing. He laboured like Faraday, oknc Hast, oJinc Kjst, and 

 his work is a monument of patient, concentrated thought, and of 

 a singleness of purpose which never swerved. 



" Experimentarian philosophers " of Graham's type (to use a 

 phrase which Hobbes of Malmesbury once flung at the progenitors 

 of the Royal Society) have very similar intellectual tendencies. 

 One is insensibly led to compare Graham with the greatest of 

 our English atomists — John Dalton. If you will turn to 

 Dr. Henry's " Life of Dalton," and read the charming 

 analysis of Dalton's mental characteristics, made by one who 

 kne.v him well and who had studied him carefully, you will find 

 that practically all that is there stated is equally applicable to 

 Graham. Both men were pre-eminently endowed with the 

 faculty of contemplating abstract relations of space and 

 number, and each began his researches with the expectation that 

 all empirical phenomena were to be brought under the control 

 of mathematical laws. Thus Dalton strove to prove that the 



