132 



Prof. S. P. Thompson on the Source 



piano of the circuit. The direction as well as the number of 

 lines of force may be altered, and this in a manner so complex 

 as almost to defy calculation, especially if the mutual induc- 

 tion between this magnetic combination and the adjacent iron 

 disk be taken into account. The figures obtained with filings 

 when the current traversed the circuit in opposite directions 

 (see figs. 2 and 3) show that the lines of force proceeding 



Kff. 1. 



Fig\ 2. 



Fig-. 3. 



outwards from the pole were in fact thus altered both in 

 number and in direction, and that, in addition to strength- 

 ening or weakening the field, the passage of the current had 

 the effect of apparently thrusting the lines of filings forwards 

 towards the iron disk or backwards from it. Moreover the 

 region separating the two separate distributions of magnetism 

 on the diaphragm was shifted on the passage of the current — 



