24-8 



ADVANCED ELECTRICITY AND MAGNETISM. 



positive cells to the left of the middle cell in Fig. 190; these two 

 positive cells have been displaced downwards with respect to the 

 middle cell, and they exert torques upon the middle cell which 

 are represented by the small curved arrows a and b. Consider 

 the two positive cells to the right of the middle cell in Fig. 190; 

 these two positive cells have been displaced downwards with 

 respect to the middle cell, and they exert torques upon the 

 middle cell which are represented by the small curved arrows c 

 and d. If the electric field is uniform (same value on both sides 

 of the middle cell in Fig. 190), then the torques a and b balance 

 the torques c and d, and the distortion which is represented in 

 Fig. 189 has no influence upon the rotatory motion of the cells. 



130. Magnetic action of a tapering electric field. Imagine an 

 electric field of which the lines of force are straight, as shown in 

 Fig. 191, but of which the intensity falls off as shown, that is to 



lines of force 

 of electric 

 field 



Fig. 191. 



say, the intensity of the electric field at any place along the line 

 AB in Fig. 191 is represented by the ordinate y of an inclined 

 straight line CD. Such an electric field is called a tapering 



