ELECTRO-MAGNETISM. 



77 



currents, being nearly at right angles to 

 the line W Q? 



(242.) When W is situated on the 

 other side of this line, as shown in fig. 

 143, the extent of the active portion of 

 the surface PQ has increased consi- 

 derably, for it now occupies the large 

 space P U ; but its power has not in- 

 creased in the same proportion, because 

 143. 



its action is more oblique, as well as 

 more distant than it was before. The 

 resultant of this action is in the direc- 

 tion W u. It is combined, however, 

 with another set of forces, those arising 

 from the unco mpen sated portion V S, of 

 the surface R S, situated between S and 

 the vertical plane W Q V. The cur- 

 rents in this portion are moving in a 

 direction contrary to that in W : their 

 action upon it is therefore repulsive, and 

 the force thence arising may be repre- 

 sented by W v, which, combined with 

 W u, gives, as a final resultant, the force 

 Wr. 



(243.) When W is placed in the pro- 

 longation of the axis of the prism, as in 

 fig. 144, it is attracted by the whole of 

 the currents in the side P Q, and re- 

 pelled by the whole of those in R S, 



'Fig. 144. 



the former giving rise to the force Wu, 

 the latter to the force W v, their result- 

 ant being W r. 



(244.) When W is in the situation 

 represented in Jig. 145, the currents 

 situated between V and S are neutra- 

 lized by those between P and U. Those 



Fig. 145. 



between R and V repel W in the direc- 

 tion of W v, while those between U and 

 Q attract it in the direction W u, forces 

 which produce the resultant Wr. 

 (245.) When W is in the prolongation 



of the line Q S,fig. 146, the currents 

 between P and Q being neutralized by 



those between V and S, the only active 

 currents are those between R and V, 

 which being repulsive, the resultant is 

 in the direction W r. 



(246.) When the situation of W is as 

 shown in fig. 14 7, the active portions of 

 the currents are' those occupying the 

 spaces RU and V S, which being both 

 repulsive, and acting according to the 

 directions Wu and Wv respectively, 

 join in producing the resultant W r. 



Fig. 147. 



(247.) Thus it appears that, combining 

 all the results of this induction, the con- 

 ducting wire is, in every situation, urged 

 by a force impelling it in the direction of 

 a tangent to the circumference of a cir- 

 cle, C, fig. 148, round the extremity of 

 the prism, P, which may therefore be 

 considered as having the functions of 



Fig. 148. 



a pole. The force thus arising pos- 

 sesses the same character of being rota- 

 tory and tangential as that which was 

 exerted on the same wire when its direc- 

 tion was parallel to the axis : and if it 

 possess this character in two directions 

 that are at right angles to each other, it 

 may fairly be inferred that the law is 

 general, and that it applies to all the 

 intermediate inclinations. 



(248.) The explanation above given 

 will be sufficient to convey a general 

 idea of the application of the theory to 



