20 



NATURE 



[September 5, 1912 



Magnetism " contributed to the " Encyclop;vdia 

 Britannica," which formed at that time the ground- 

 work of our studies at Cambridge under Sir J. J. 

 Thomson. Jt would be difficult to find a more com- 

 plete and concise statement of the mathematical 

 theory at the time when that article was written. 

 One can well understand the value of such a teacher, 

 and sympathise with his university in the loss they 

 have sustained. 



John Brown, F.R.S., who acted as local secretary 

 for the Association at Belfast in 1902, will be remem- 

 bered for his work on the Volta contact effect between 

 metals, which he showed to be in the main dependent 

 on chemical action, and to be profoundly affected by 

 the nature of the gas or other nicdium in which the 

 plates were immersed. .Although the theory of this 

 difficult subject may not yet be completely elucidated, 

 there can be little doubt that his work takes the first 

 rank on the e.xperimental side. 



William Sutherland, D.Sc, who at one time acted 

 as Professor of Physics at Melbourne, is best known 

 for his familiar papers on the subject of molecular 

 physics in The Philosophical Magazine. His work 

 was always remarkable for its wide range and bold- 

 ness of imagination. Many of his hypotheses cannot 

 yet be weighed in the balance of experiment, but some 

 have already been substantiated. For instance, his 

 theory of the variation of viscosity of gases with 

 temperature has been generally accepted, and results 

 are now commonly expressed in terms of Sutherland's 

 constant. 



Osborne Reynolds, the first Professor of Engineer- 

 ing at Owens College, was President of Section G 

 in 1887, but belongs almost as much to mathematics 

 and physics, in which his achievements are equally 

 memorable. It would be scarcely possible for me to 

 enumerate his important contributions to the science 

 of engineering, which will be more fittingly com- 

 memorated elsewhere. His mastery of mathematical 

 and physical methods, while contributing greatly to 

 his success as a pioneer in the engineering laboratorv, 

 enabled him to attack the most diflicult problems in 

 physics, such as the theory of the radiometer and the 

 thermal transpiration of gases. His determination 

 of the mechanical equivalent of heat is a most striking 

 example of accurate physical measurement carried out 

 on an engineering scale. His last great work, on the 

 " Submechanics of the Universe," is so original in its 

 ideas and methods that its value cannot yet be fullv 

 appreciated. While it differs so radically from our 

 preconceived ideas that it fails to carry immediate 

 conviction, it undoubtedly represents possibilities of 

 truth which subsequent workers in the same field 

 cannot afford to ignore. 



The present year has been one of remarkable 

 activity in the world of mathematical and phvsical 

 science if we may measure activity bv the number 

 and importance of scientific gatherings like the present 

 for the interchange of ideas and the general advance- 

 ment of science. The celebration of the 250th anni- 

 versary of the foundation of the Royal Society brought 

 to our shores a number of distinguished delegates 

 from all parts of the world, to promote the ever- 

 growing fellowship among men of science which is 

 one of the surest guarantees of international progress. 

 The Congress of Universities of the Empire brought 

 other guests from distant British dominions, and con- 

 sidered, as one of the principal points in its pro- 

 gramme, the provision of facilities for the interchange 

 of students between different universities, which will 

 doubtless prove particularly advantageous to the 

 scientific student in the higher branches of re- 

 search. In the special branches of knowledge more 

 particularly associated with this section, the Inter- 

 national Congress of Mathematics at Cambridge, 



NO. 2236, VOL. go] 



while it affords to Cambridge men like myself a most 

 gratifying recognition of our alma mater as one of 

 the leading schools of mathematics in the world, has 

 given us the opportunity of meeting here a number of 

 distinguished foreign mathematicians whose presence 

 and personality cannot be otherwise than inspiring to 

 our proceedings, and will compensate for any 

 deficiency in our own mathematical programme. The 

 Optical Convention held this year in London, by the 

 importance of the papers contributed for discussion, 

 and by its admirable exhibition of British instruments, 

 has revealed the extent of our optical industry and 

 talent, and has done much to dispel the impression, 

 fostered by an unfortunate trade regulation, that the 

 majority of optical instruments were " made else- 

 where." The Radio-Telegraphic Conference, held 

 under the auspices of the British Government, has 

 formulated recommendations for regulating and ex- 

 tending the application of the discoveries of modern 

 physics for saving life and property at sea. The work 

 of this Conference will be fittingly supplemented on 

 the scientific side by the discussion on wireless tele- 

 graphy which has been arranged to take place in this 

 section in conjunction with Section G. 



It would be impossible, even if it were not out of 

 place, for me to attempt to review in detail the im- 

 portant work of these congresses, a full account of 

 which will shortly be available in their several reports 

 of proceedings now in course of publication. In the 

 present age of specialisation and rapid publication it 

 would be equally impossible to give any connected 

 account in the time at my disposal of recent develop- 

 ments in those branches of science which come within 

 the range of our section. The appropriate alterna- 

 tive, adopted by the majority of my predecessors in 

 this chair, is to select some theory or idea, sufficiently 

 fundamental to be of general interest, and to discuss 

 it in the light of recent experimental evidence. It ma}' 

 sometimes be advantageous to take stock of our funda- 

 mental notions in this way, and to endeavour to deter- 

 mine how far they rest on direct e.xperiment, and how 

 far they are merely developments of some dynamical 

 analogy, which may represent the results of experi- 

 ment up to a certain point, but mav lead to erroneous 

 conclusions if pushed too far. With this object I 

 propose to consider on the present occasion some of 

 our fundamental ideas with regard to the nature of 

 heat, and in particular to suggest that we might with 

 advantage import into our modern theory some of the 

 ideas of the old caloric or material theory which has 

 for so long a time been forgotten and discredited. In 

 so doing I may appear to many of vou to be taking a 

 retrograde step, because the caloric theory is generally 

 represented as being fundamentally opposed to the 

 kinetic theory and to the law of the conservation of 

 energy. I would, therefore, remark at the outset that 

 this is not necessarily the case, provided that the 

 theory is rightly interpreted and applied in accordance 

 with experiment. Mistakes have been made on both 

 theories, but the method commonly adopted of select- 

 ing all the mistakes made in the application of the 

 caloric theory and contrasting them with the correct 

 deductions from the kinetic theory has created an 

 erroneous impression that there is something funda- 

 mentally wrong about the caloric theory, and that it is 

 in the nature of things incapable of correctly repre- 

 senting the facts. I shall endeavour to show that this 

 fictitious antagonism between the two theories is with- 

 out real foundation. They should rather be regarded 

 as different ways of describing the same pheno- 

 mena. Neither is complete without the other. The 

 kinetic theory is generally preferable for elementary 

 exposition, and has come to be almost exclusively 

 adopted for this purpose ; but in many cases the 

 caloric theory would have the advantage of emphasis- 



