132 



ON MAGNETISM. 



48. It is evident here that B is converted 



into a magnet as long as it is under the 

 influence of A, and no longer. And this 

 A is the characteristic of Transient Induced 

 Magnetism. If the quality of the magnet- 

 ism of the lower end of B be examined 

 B by the disturbance which it produces in a 

 compass-needle, it is found to be the same 

 as that of the lower end of A (blue magnet- 

 ism, in the diagram). This leads to the 

 presumption, in analogy with other phseno- 

 mena of magnetism, that the magnetism of 

 the upper end of B is of the kind opposite to that 

 of the lower end of A: a, presumption which we shall 

 find to be supported in the case which we can examine 

 more perfectly, that of transient induction produced by 

 the earth's action. 



Fig- 49- The same conclusions will 



W 



be arrived at by examination 

 ^^ of the deviation produced in a 

 suspended magnet or compass- 

 needle ; as in Figure 49. If 

 the magnet A has produced 

 deviation of B' to the position 

 shewn in the diagram, and the 

 bar of soft iron B be inserted 

 (under circumstances where, if 

 alone, its effect on B would be 

 imperceptible), it greatly in- 

 creases the deviation of B'. 



