v. m ] 



XYIII. Notices respecting New Books. 



Theorie de V Electricite. By A. Yaschy. Paris : Baudry et 

 Oie., 1896. 



TN this treatise M. Yaschy presents a purely mechanical theory 

 ■*■ of electricity founded on the fact, experimentally demon- 

 strated, that an electric field with a measurable intensity exists at 

 every point of space. The connexion between electric intensity 

 and the medium in which it is manifested is not considered; on 

 this point the author remarks : — " The idea of intensity of the 

 electric field is not more intimately connected with the three 

 fundamental ideas of mechanics than these latter are connected 

 among themselves. We shall therefore consider it as fundamental ; 

 but all others with which we meet in electricity will be derived 

 from it, and from length, time and mass." 



It is shown that the condition of stability of the electric field is 

 the existence of a potential function ; this leads to the discussion 

 of lines of force, equipotential surfaces and conductors. M. Yaschy 

 distinguishes two classes of action at a distance, of which the 

 action between two electric charges and that of an element of a 

 linear current on a magnet pole are the types ; in the former case 

 the force is in the line joining the particles, whereas in the latter 

 case one of the attracting " masses " is a vector quantity, and its 

 direction determines that of the force. The two classes may be 

 called Newtonian and Laplacian respectively ; the author shows 

 that any field of force whatever can be completely represented by 

 a suitable distribution of Newtonian and Laplacian masses, with 

 an inverse square law of attraction : a stable field is due only to 

 Newtonian masses, while a solenoidal distribution is produced by 

 Laplacian masses alone. The energy which really exists in every 

 unit of volume of the field is referred in action-at-a-distance 

 theories to these fictitious masses, thus giving rise to the ideas of 

 electric charges and currents. 



M. Yaschy's explanation of a current in a conductor is analogous 

 to that of Poynting ; in every element of volume of the conductor, 

 the energy of the electric field is constantly being transformed 

 into heat, and new energy must be supplied along definite paths 

 from the battery or other source of electric energy. Assuming 

 that the rate of supply of energy to the element of volume depends 

 only on the instantaneous state of the field at its surface, and not 

 on the mode of transformation of the energy within it, the field of 

 a current can be divided into an electrostatic and a magnetic 

 portion. The discussion of variable currents follows, and the 

 detailed treatment of electric waves is a prominent feature in the 

 book. 



