the Laws of Magnetic Forces. 303 



39. We may conclude from these investigations (37, 38), that 

 the actual force exerted between a magnet and a mass of iron 

 is directly proportional to the force induced in the iron, and in- 

 versely proportional to the distance, all other things being the 

 same ; and this leads us more immediately to consider the abso- 

 lute attractive force of a magnet and a mass of iron, the dis- 

 tances between the iron and magnet, and the force induced in 

 the iron, being both variable. 



This case of magnetic attraction, which applies immediately to 

 the general law, as determined by the celebrated COULOMBE, and 

 likewise by many other profound inquirers, is readily investigated, 

 by placing a magnet to act directly on the suspended cylinder of 

 soft iron #, as in Fig, 1., at different distances, by which means 

 we vary the induced force in the iron x, and the distance simul- 

 taneously. Thus, if we decrease the distance, Fig. 1, one-half, 

 we double the force induced in x (19), whilst we diminish the 

 distance in the ratio of 2 : 1 . If we decrease the distance to one- 

 third, we treble the force in the iron x, and at the same time dimi- 

 nish the distance in the ratio of 3 : 1 , and so on : the absolute or 

 total attractive forces will consequently, from what has been al- 

 ready stated (37, 38.), be respectively in the ratio of 4 : 1 and 

 9:1; and hence we obtain a final force, which is observed to 

 vary in the inverse ratio of the squares of the distances between 

 the attracting bodies. Thus, when a long cylindrical magnet in 

 Fig. 1 . not greatly exceeding the suspended iron ae in diameter, 

 was placed immediately under it, the distance being an inch, the 

 force indicated amounted to 5. On diminishing the distance 

 to half an inch, the index moved forward to 20. 



general law of magnetic attraction about to be demonstrated, namely, that of the 

 inverse square of the distance ; yet, on examination, and as will be further shewn, it 

 will be found to depend exclusively on the operation of induction, and that where 

 this operation does not proceed, the law above named no longer obtains. 



