294 



ELEMENTARY LESSONS ON [CHAP. v. 



wards. On the whole, therefore, PQ will be urged to- 

 wards CD. The portions PR and RS will experience 

 forces of rotation however, P being urged round R as a 



Fig. 122. 



centre towards C, and R being urged horizontally round 

 S towards C. These actions would tend to make AB 

 parallel with CD. 



334. Ampere's Theory. From the four preceding 

 experimental data, Ampere built up an elaborate mathe- 

 matical theory, assuming that, in the case of these forces 

 acting apparently at a distance across empty space, the 

 action took place in straight lines between two points, 

 the total attraction being calculated as the sum of the 

 separate attractions on all the different parts. The 

 researches of Faraday have, however, led to other views, 

 and we now regard the mutual attractions and repulsions 

 of currents as being due to actions taking place in the 

 medium which fills the space around and between the 

 conductors. That space we regard rather as being full 

 of curving " lines of force." Every wire carrying a 

 current has a magnetic field, like that of Fig. 85, sur- 

 rounding it ; and every closed circuit acts as a magnetic 

 shell. Hence all these electrodynamic actions are 

 capable of being regarded as magnetic actions, and they 

 can be predicted beforehand for any particular case on 

 that supposition. Thus, the author of these Lessons 



