558 



NA TURE 



[October 21, 1922 



Tendencies of Modern Physics. 



THE Swiss Society of Natural Sciences met this 

 year at Berne on August 24 to 27. The 

 programme of the session comprised several discus- 

 sions on questions of general interest, and papers 

 of a more special character communicated to the 

 various sections. The work was divided between 

 the following sections : (1) Mathematics; (2) Physics; 

 (3) Geophysics, Meteorology, and Astronomy; (4) 

 Chemistry ; (5) Geology, Mineralogy, and Petrography ; 

 (6) Botany ; (7) Zoology ; (8) Entomology; (9) Palaeon- 

 tology; (10) Anthropology and Ethnology ; (11) Medical 

 and Biological Science; (12) History of Medicine and 

 Natural Science ; (13) Veterinary Science ; (14) Phar- 

 macy; (15) Engineering History. 



We cannot give here a detailed account of this 

 annual event in Swiss science ; we shall therefore 

 confine ourselves to a resume of the address of Prof. 

 C. E. Guye, of Geneva, in opening the series of 

 general discussions. 



Taking the title, " The Tendencies of Modern 

 Physics and the Conception of Matter," Prof. Guye 

 first showed that modern physics was becoming 

 more and more electromagnetic, discontinuous, and 

 statistical. To these three characteristics, which have 

 been sufficiently disconcerting to minds accustomed 

 to the classical conceptions of the second half of the 

 nineteenth century, there has now been added a 

 fourth, of still more perplexing character, in the 

 introduction of the principle of relativity. In adopt- 

 ing this principle physics has displayed a distinctly 

 metaphysical tendency, which sometimes venturi 3 to 

 introduce into scientific discussion a dogmatic method 

 of procedure. It is true that the difficulty is com- 

 pensated by important advantages, resulting from 

 the fact that the formula: of relativity introduce more 

 simplicity in the dynamics of very great velocities, 

 and more unity between the various branches of 

 physics. 



After having shown how physics, like chemistry, 

 has moved steadily along the path of discontinuity 

 by the introduction of the atom of electricity and 

 the theory of quanta, Prof. Guye spoke of the con- 

 sequences of this discontinuity, which complicated 

 greatly the explanation of phenomena apparently of 

 the most simple character. 



How, indeed, could one follow, by means of the 

 equations of mechanics, the reciprocal actions of a 

 nearly innumerable group of discontinuous elements 

 (molecules, atoms, electrons) ? This extreme compli- 

 cation which characterises the phenomenon, apparently 

 so simple, when it is desired to study it intimately, 

 led to the introduction of kinetic theories. The 

 calculus of probabilities then came to the aid of 

 physicists, powerless as they were to solve, by means 

 of the equations of mechanics, the inextricable 

 problems which were proposed to them. But the 

 consequence of these kinetic theories is to lead us 

 to conceive physico-chemical laws as statistical, so 

 that we must picture physico-chemical determinism 



as a statistical determinism, to which the law of 

 great numbers imparts all the appearance of infinite 

 precision. 



The progress of physics towards electromagnetism 

 is particularly striking. The first decisive step along 

 this path was made by Maxwell, to whom we owe 

 the electromagnetic theory of light, which, universally 

 accepted as it is to-day by physicists, unites in a 

 systematic whole the phenomena of light and of 

 electromagnetism. But this tendency to explain 

 physical phenomena by the laws of electromagnetism 

 has only served to make it still more accentuated. 

 It has even attacked the mechanics which seemed 

 to be the immutable basis of the old physics. To-day 

 the fundamental postulate of mechanics — inertia — 

 can be satisfactorily explained in terms of the pro- 

 perties of an electromagnetic field, and more and 

 more intermolecular forces appear to be of electro- 

 magnetic nature (Debye, Keesom). 



But the main reason for this constant evolution 

 of physics towards electromagnetism is the work 

 carried out particularly in England (Rutherford's 

 school), which has exhibited it in a most convincing 

 fashion. The material atom itself appears to be 

 constituted entirely of charges of electricity, positive 

 and negative (electrons), and all physical forces, 

 with the exception of the mysterious force of gravita- 

 tion, will thus be found, in the last resort, to be 

 electric and magnetic forces. 



In the second part of his address, Prof. Guye 

 showed how the conception of matter, as defined by 

 inertia, had evolved from Lavoisier to Einstein, and 

 to the most recent work of Rutherford and Aston. 

 Without committing ourselves positively to Prout's 

 hypothesis, which would make the atomic weights 

 of the elements integral multiples of that of a unique 

 constituent — the atom of hydrogen — new develop- 

 ments point to a duality of ultimate material, the 

 positive electron which is mainly responsible for the 

 inertia of the atom, and the negative electron. 



In short, the startling progress realised in physics 

 during the last thirty years has reduced to naught 

 all those fluid phantoms which we knew — imponder- 

 able electric and magnetic fluids; only the most 

 tenacious among them — the aether — offers still a 

 partial resistance. 



Physicists have thus been led, little by little, to 

 the idea of the materiality of electricity, and still 

 more the formula; of relativity point to the parallelism 

 between inertia and energy ; that is, to the fusion 

 into a single principle of the two principles which 

 govern all physical phenomena — the principle of the 

 conservation of mass and that of the conservation 

 of energy. 



Such are the important results, not only from the 

 scientific point of view, but also from that of our 

 best philosophic culture, wdtich modern research has 

 brought forward during the course of the last thirty 





The Isothermal Frontier of Ancient Cities. 1 



THE northern frontier of the Roman Empire is 

 *■ shown in atlases of ancient geography, and that 

 of the Achaemenian Empire of the Persians and of 

 the dynasties which succeeded in the Middle East. 

 The frontier of the ancient Chinese Empire has not 

 been made similarly familiar, and in place of it there 

 is the representation of the Empire of China as it 



1 Abstract of a paper by Dr. Vaughan Cornish read before Section E 

 (Geography) of the British Association at Hull on Sept. 12. 



NO. 2/64, VOL. I IO] 



has been in mediaeval and modern times. From this 

 most of Manchuria, all Mongolia, and the Hi valley 

 must be shorn off in order to get the Chinese northern 

 frontier as it was under the Han dynasty in the 

 beginning of the second century after Christ, the 

 age of the Antonines in Europe. At this time, when 

 the ancient civilisation of Eurasia was at the height 

 of its culture and apparently at the maximum of 

 its power, the northern frontier once controlled by 



