Action of Electric and Magnetic Fields on Electrons. 721 



by Hallwachs, in addition to the work o£ his predecessors, 

 there seems little doubt that the simpler idea o£ changes in 

 the absorptive power of electrified double-layers and other 

 films of gases of great density near the surface of the metals, 

 is the probable cause of fatigue. And the experiments 

 described in this paper show no reason for not accepting the 

 same hypothesis to explain the changes occurring in this type 

 of secondary radiation. 



I take great pleasure in thanking Professor Thomson for 

 his advice and for his many courtesies to me during my visit 

 to the Cavendish Laboratory. 



Cavendish Laboratory, Cambridge, 

 March 1907. 



LXIII. The Action of Uniform Electric and Magnetic Fields 

 on Moving Electrons. By A. H. Bucherer, D.Sc, Bonn 

 University* . 



IN my paper on a new principle of relativity in electro- 

 magnetism (Phil. Mag., April), in which I have 

 calculated the forces acting on moving electrons in the 

 uniform fields of electromagnets and of condensers, I have 

 omitted to call special attention to the circumstance that the 

 expressions obtained do not apply to all kinds of uniform 

 fields. In fact, as will be evident at once from the reasoning- 

 adopted by me, I.e., the forces on the electrons primarily 

 depend on the distribution of electric and magnetic masses, 

 and indirectly only on the intensities of the fields in which 

 they are moving. Thus electrons moving in various uniform 

 fields of the same intensity will in general experience different 

 forces if these fields are due to different distributions of 

 electric and magnetic masses, special care being requisite with 

 solenoids which must be replaced by equivalent magnetic shells. 

 Closely connected with this is another important conse- 

 quence. Let an electron move in the uniform superimposed 

 fields Hq' and JL n of two electromagnets. Then, to find the 

 resultant force, it is not permissible to substitute the resultant 

 field Hf/" in the expression given by me. For evidently 



VH/n , VH/'u VH '"u ' . 



1 - % cos 2 (H 'n) l-~ 2 cos 2 (H "n) ' 1- % cos 2 (H '"u) 



V V V 



I am preparing experiments with Becquerel rays in order 

 to test the formulas derived by me from the principle of 

 relativity. 



Bonn University, April 1907. 



* Communicated by the Author. 

 Phil. Mag. S. 6. Vol. 13. No. 78. June 1907. 3 C 



