442 Messrs. V. Cremieii and H. Pender on 



reaction through the springs, from their force on //?, by which 

 7n acts on the ether (always admittedly an unreal kind of 

 agency, invoked only by way of dynamical illustration). In 

 the new electric design, m acts directly on the ether, by 

 inertia, in simple proportion to acceleration of relative 

 motion. 



It is interesting to see that every one of the formulas of 

 §§ 240. 241 (with the new notation of a:, in the old dynamical 

 problem), are applicable to both the old and the new subjects : 

 and to know that the solution of the problem in terms of 

 periods is the same in the two cases, notwithstanding the 

 vast difference between the artificial and unreal details of 

 the mechanism thought of and illustrated by models in 1884. 

 and the probably real details of ether, electricity and ponder- 

 able matter, suggested in 1900-1903. 



§ 243. The interesting question of energy referred to in 

 Lee. X.^ U. 18-21 of p. Ill becomes more and more inter- 

 esting now when we seem to understand its real triple 

 character in (I) kinetic energy of pure ether, (II) potential 

 energy of elasticity of ether, and (III) electric potential 

 energy of mutual repulsions of electrions and of attractions 

 between electrions and atoms. It is slightly and imperfectly 

 treated in App. L. For the present I must leave it with 

 much regret, to allow this Volume to be prepared for 

 publication. 



LYIII. On tlie Magnetic E^^ect of Electric Convection. 

 By YlCTOR CeeMIEU and HaEOLD PE^'DEE ■^. 



A DETAILED discussion of the present state of the 

 question of electric convection has been recently 

 given by Cremieu in the December number of the Journal 

 de Physique. Contradictory results have been obtained : 

 some seeming to prove the existence of a magnetic field 

 around a moving charged bodv ; others seeming to prove 

 the non-existence of such an effect. 



In the same article, the conditions necessary for a proper 

 experiment on electric convection have been clearly set 

 forth. We shall recall that the realization of the following 

 conditions is necessary : — 



1. That the charge is actually carried along [entrainee] by 

 the body in motion. 



2. That this charge alone can act upon the apparatus 



* Eead to the Societe francaise de Physique, seance du 17 Avril, 



1903 : commuaicated br the Authors. 



