the Laws (/Magnetic Forces. 309 



the force induced in A, and inversely proportional to the distance 

 N* (37, 38*.) ; and this must be still true, though A be supposed 

 also a magnet, seeing that the inductive action still proceeds 

 (43.) ; and thus the absolute force of B upon A will vary as be- 

 fore (39.) ; but A being now supposed also permanently magne- 

 tic, it exerts a similar force on B, and which will consequently 

 vary in the same way. Therefore, the whole attractive force be- 

 tween A and B will still be found to vary in an inverse ratio of 

 the square of the distance, supposing the inductive action to go 

 on uniformly. And this will be true, whatever be the relative 

 magnetic intensities, the only difference between this action and 

 that exerted between a magnet and a mass of iron, arising from 

 the circumstance, that, in the latter, there is only one primary 

 inductive action in the operation, whilst in the other there are 

 two. 



46. In order to investigate the absolute force of attraction 

 or repulsion, as exerted between two magnetised bodies, the dis- 

 tances and induced forces being both variable, it is only neces- 

 sary to substitute a small magnet for the cylinder of soft iron x, 

 Fig. 1., and observe the attractive or repulsive forces by approxi- 

 mating toward it either the similar or dissimilar poles of another 

 magnet, in the way before described (39.) 



We have already considered (17.) some of the circumstances 

 likely to interfere with the accuracy of an experiment thus ar- 

 ranged, and we have shewn that a limit may be determined, 

 without which the action of the other poles may be supposed of 

 no assignable value. It remains, however, still to be considered, 

 what subsequent change is likely to be produced in this limit 

 cd, Fig. 6, 7, 8., by the inductive action of the similar or dissimi- 

 lar polarities on each other. Now, it was shown (33.), that the 

 inductive influence of dissimilar polarities lessens their free ac- 

 tion : the approximation of the polarity N towards s will there- 



Q q 2 



