the Laws of Magnetic Forces. 301 



the iron be as a magnet, that the distance a b between a mag- 

 net and a mass of iron being constant, the absolute attractive 

 force will be directly proportional to the power of the mag- 

 net be, and consequently to the force induced in the iron ac. 

 Thus, if two magnets, whose separate forces of induction on a 

 mass of soft iron, at a constant distance, have been previously 

 well determined, be opposed to the suspended iron x, as in Fig. 1, 

 then the respective attractive forces, at a constant distance, as 

 shewn by the index, will be observed to vary in the same ratio 

 as before ; and if both the magnets be now conjoined and op- 

 posed to the suspended iron x, at the same distance, then the 

 indicated attractive force will be the sum of the two former 

 forces, or very near it. 



38. That the absolute force of attraction exerted between a 

 magnet and a mass of iron should vary with the power of the 

 magnet, and consequently with the force induced in the iron, 

 all other things remaining the same, is what might have been 

 previously supposed ; but the ratio in which this same force of 

 attraction might be expected to vary, when the force induced 

 in the iron ae, Fig. 1, is a constant quantity, whilst its distance 

 from a magnet H is variable, the magnetism of II being either 

 temporary or permanent, is not so apparent ; nor has such a case> 

 as far as I am aware, been yet contemplated ; beside, that the 

 possibility of obtaining satisfactorily all the conditions of such an 

 experiment would appear at first somewhat doubtful. The re- 

 sults, however, before given (19), enable us to investigate expe- 

 rimentally such a case. Thus, by varying the distance cd, Fig. 5, 

 between a magnet and a mass of iron, we can, as before ob- 

 served (24), within certain limits, obtain any relative magnetic 

 intensity required ; and by varying the distance ab between the 

 temporary magnetic pole of the iron be, and the iron x, we can 

 preserve the force induced in x constant. Thus, if we dimi* 



p p 2 



