﻿1122 Mr. 'S. J. Barnett on Electric Fields due to the 



looking in the direction of v the circles are right-handed 

 behind the central plane, left-handed in front. In this field 



<£= -(Aw) = 0, the electric field is circuital, without charges, 



and E= - |^ = -OV)A= - [Bvl. 



c ot c c 



The lines of electric intensity are left-handed circles centered 

 on the axis in planes normal thereto. 



§ 10. The introduction of conductors (with negligible 

 magnetic susceptibility) moving rigidly with the system B, 

 and uncharged in B, does not affect the electric field pro- 

 duced by the motion in any way at points not within the 

 material of the conductors. For it does not alter A' = A, 

 and therefore does not alter — \/(Av) or (i>V)A. Thus, if in 

 the field of § 3 a closed conducting box, moving with the 

 current sheets, were to surround the observer in C, the electric 

 intensity observed would remain unaltered. It is therefore 

 unnecessary to inquire whether the substances in B are 

 conducting or insulating. If they are magnetic, the vector 

 potentials of the magnetons will have to be taken account of. 



Another way of looking at the matter is, of course, this : 

 The introduction of the conductors and the consequent 

 induction of electric charges upon them may greatly affect 

 the intensity at P due to the motion. But the effect of these 

 charges is entirely neutralized by the distribution produced 



by the motional intensity - [«B] acting in and upon the 



c 



conductors themselves. Within the material of the con- 

 ductors forming a part of the system B, or rigidly moving 

 with B, the total electromotive intensity is 



F= - (vV)A- - V(AtO + - [vB] = - [Br] + - [>B] =0. 

 c c c c ■ c 



§ 11. In the case of a conducting cylinder or sphere with 

 uniform intensity of magnetization I in motion normal to the 

 magnetic axis, all the formulae, for points outside the system, 

 are exactly similar to those for the cylindrical and spherical 

 current sheet, but I has now the meaning attached to it here 

 instead of that of §§7 and 8. Within the material of the 

 system the electromotive intensity is zero. 



If we apply to the magnetic elements, or magnetons, the 

 same method previously applied to the whole current sheet, 

 we evidently find that each magneton with component mag- 

 netic moment ^ parallel to the magnetic axis becomes so 



