NA TURE 



529 



THURSDAY, APRIL 5, ic 



IONS, ELECTRONS, AND CORPUSCLES. 



Lcs Ouaittites 6lem.enta.ires d'Electricite : Ions, Elec- 

 tions. Corpuscles. Memoires reunis et publics 

 par Henri Abraham et Paul Langevin. Two 

 volumes. Pp. xvi+1138. (Paris: Gauthier-Villars 

 et Fils, 1905.) Price 35 francs. 



THIS very important work, which has been brought 

 out by the French Physical Society under the 

 joint editorship of MM. Abraham and Langevin, con- 

 sists of a series of digests of the memoirs on which 

 the foundation of the electrodynamic theory of matter 

 is laid. In some cases risume's of their researches 

 have been written especially for this work by the 

 original authors, but in the majority of instances the 

 papers have been dealt with by abstractors. The 

 value of this method depends entirely on the insight 

 which is brought to bear upon it, and the task must 

 have been particularly difficult in the present instance 

 owing: to the great variety of the material concerned, 

 since many of the investigations are purely experi- 

 mental, whilst others require all the skill in abstract 

 reasoning possessed bv the pure mathematician. The 

 excellence which we should expect from the names 

 of the editors, one of whom, M. Langevin, has himself 

 made extensive and valuable contributions to the 

 subject, is completely justified by the result. When- 

 ever it was consistent with the necessary brevity, the 

 abstractors have kept to the original words of the 

 author, and,, so far as the reviewer has been able to 

 discover, no author can claim that his views have 

 In in misrepresented in any important particular. 



The book will be heartily welcomed bv all who are 

 interested in the development of the electron theory, 

 whether it be in its most general aspect as a funda- 

 mental theory of physical phenomena or in its ex- 

 tremely interesting applications to such complex 

 branches of the subject as the conduction of electricity 

 through gases and radio-activity. It is true that we 

 have a number of books, such as J. J. Thomson's 

 " Conduction of Electricity through Gases " and 

 " Electricity and Matter," Larmor's " /Ether and 

 Matter," Poincare's " Electricite et Optique," Stark's 

 "Die Electrizitiit in Gasen," and Rutherford's 

 " Radio-activity," which in one way or another con- 

 tain the whole of the material of the two volumes 

 under review ; but in these cases the material has 

 usually been selected, often, of course, with gain ol 

 interest, so as to emphasise the point of view of the 

 particular author. In the present work, on the con- 

 trary, we are furnished w-ith an account of each por- 

 tion of the subject as it developed itself in the mind 

 of its discoverer. The work therefore fills a distinct 

 lacuna in the literature of the subject. 



Recent advances in electrodynamics have placed the 

 fundamental principles of physics in an interesting 

 but not altogether satisfactory position. By consider- 

 ing the energy of the electric field, J. J. Thomson 

 showed, many years ago, that a moving electric 

 charge possessed a spurious mass due to the disturb- 

 NO. IOOI, VOL. 73] 



ance it created in the ether through which it was 

 moving. This idea has been more than confirmed 

 by the experiments of Kaufmann on the mass of 

 the Becquerel rays or negative electrons. These ex- 

 periments show that the whole of the mass of these 

 electrons is of electrical origin, and is due entirely to, 

 the motion of their electric charges. The work of 

 Lorentz and Larmor has given very good reasons for 

 supposing that all matter consists solely of electrons, 

 so that we are forced to the conclusion that the mass 

 of all matter is due to the electrical charges of its, 

 ultimate particles. 



The reasoning by which this result has been arrived 

 at is dynamical in character, and is therefore based' 

 on mass, space, and time as fundamental conceptions. 

 Thus, by the application of a system of thought in 

 which mass is a fundamental conception, we have 

 succeeded in resolving the idea of mass into some- 

 thing, viz. electricity', which lies outside the system. 



There appear to be two ways of escape from the 

 confusion implied by this paradoxical result. The 

 first is to resolve electricity into the mass motion of 

 a mechanical ether, and thus to make everything 

 again consistent with the fundamental laws of me- 

 chanics. Attempts to construct a dynamical theory 

 of the ether have continually been made ever since 

 the ether began to figure in the literature of exact 

 science. The most successful hitherto has been that 

 of Larmor, which made the ether a perfect fluid com- 

 posed of gyrostatic atoms. According to this view, 

 which has been criticised by Poincare in his " Elec-. 

 tricite et Optique," the velocity of the ether is along 

 the lines of magnetic force. We have, however, good' 

 grounds for thinking that the drift velocity of the 

 ether is proportional to the vector product of the. 

 electric and magnetic forces, and it is probable that 

 the successful ether theory will furnish an explanation. 

 of this result. 



The second way of escape is to take the equations 

 of the electromagnetic field as ultimate relations, 

 which are empirically given and of which there is no. 

 "explanation." By making energy the fundamental 

 conception, we could then obtain a consistent scheme 

 which would not involve the idea of mass in any 

 fundamental way. The equations of motion of any 

 material system could then be obtained bv an appro- 

 priate variation of the energy function, which of 

 course contains only electric and magnetic terms,, 

 and the results expressed in terms of force subse- 

 quently if required. On this view the momentum 

 in any system is obtained as the volume integral of 

 the vector product of the electric and magnetic forces, 

 and mass is simply the vector coefficient which results 

 on dividing the increase in this by the corresponding 

 increase in velocity. This method of stating the case, 

 which makes mass a very secondary conception, will 

 at once be recognised as our old friend the " ener- 

 getic " view of things, and the electrodynamic ex- 

 planation of mass may justly be regarded as a great 

 triumph for energetics. The considerations which 

 have been brought forward in the preceding para- 

 graph show, however, that the solution in terms of 



A A 



