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TRANSACTIONS OF THE SECTIONS. 



Section A.— MATHEMATICAL AND PHYSICAL SCIENCE. 



President of the Section — 

 Professor Sir William Thomson, M.A., LL.D., D.C.L., F.E.S.L. & E., F.R.A.S. 



THURSDAY, AUGUST 28. 



The President delivered the following Address: — 



Steps towards a Kinetic Theory of Matter. 



The now well-known kinetic theory of gases is a step so important iu the way of 

 explaining seemingly static properties of matter by motion, that it is scarcely 

 possible to help anticipating in idea the arrival at a complete theory of matter, in 

 which all its properties will be seen to be merely attributes of motion. If 

 we are to look for the origin of this idea, we must go back to Democritus 

 Epicurus and Lucretius. We may then, I believe, without missing a single 

 step, skip ],800 years. Early last century we find in Malebranche's 

 ' Recherche de la Yerite,' the statement that ' La d arete des corps ' depends on 

 ' petits tourbillons.' l These words, embedded in a hopeless mass of unintel- 

 ligible statements of the physical, metaphysical, and theological philosophies 

 of the day, and unsupported by any explanation, elucidation, or illustration 

 throughout the rest of the three volumes, and only marred by any other single 

 sentence or word to be found in the great book, still do express a distinct concep- 

 tion, whicb forms a most remarkable step towards tbe kinetic theory of matter. 

 A little later we have Daniel Bernoulli's promulgation of what we now accept as 

 a surest article of scientific faith — the kinetic theory of gases. He, so far as I 

 know, thought only of the Boyle's and Harriot's law of the 'spring of air,' as 

 Boyle called it, without reference to change of temperature or tbe augmentation 

 of its pressure if not allowed to expand for elevation of temperature, a phenomenon 

 which perhaps he scarcely knew, still less the elevation of temperature produced 

 by compression, and the lowering of temperature by dilatation, and the consequent 

 necessity of waiting for a fraction of a second or a few seconds of time (with 

 apparatus of ordinary experimental magnitude), to see a subsidence from a larger 

 change of pressure, down to the amount of change that verifies Boyle's law. The 

 consideration of these phenomena forty years ago by Joule, in connection with 

 Bernoulli's original conception, formed the foundation of the kinetic theory of 

 gases as we now have it. But what a splendid and useful building bas been 

 placed on tins foundation by Clausius and Haxwell, and what a beautiful orna- 

 ment we see on tbe top of it in the radiometer of Crookes, securely attacked to it 



1 ' Preuve de la supposition que j'ay faite : Que la inatiere subtile ou eth^ree est 

 necessairement composee de petits tourbillons ; et qu'ils sont les causes natu- 

 relles de tous les changements qui arrivent a la matiere ; ce que je confirme par 

 l'explication des effets les plus generaux de la Physique, tels que sont la durettj des 

 corps, leur fluidity, lew pesanteur, leurlegerete, lalumiere et la refraction et reflexion 

 de scs rayons.' — Malebrancke, Recherche de la Verite, 1712. 



