302 Mr HARRIS'S Experimental Inquiries concerning 



nish cd one-half, we double the force in be ; and if the dis- 

 tance ab was preserved, the force in ac would become likewise 

 doubled (29) ; but if, whilst we diminish cd one-half, we double 

 ab, then (19) the force in x will remain as before. We may 

 thus preserve the induced force in the iron x a constant quan- 

 tity, whilst its distance from the inductive magnet be is a va- 

 riable one ; and hence arrive at the reciprocal force of attrac- 

 tion under these conditions. The experiment being thus ar- 

 ranged, it was clearly shewn, that the absolute force varied with 

 the distance, the induced force in the iron being a constant quan- 

 tity. Thus, by diminishing cd one-half, so as to double the 

 magnetic intensity of be, and at the same time doubling the dis- 

 tance ab, the number of degrees marked by the index were as 

 two to one. By decreasing c d to one-third, and trebling a b, 

 the observed forces were as three to one ; and so on. 



This curious fact was not only apparent when the magnetic 

 force was varied by induction, but was also satisfactorily shewn, 

 when varied by magnets whose relative powers of induction were 

 previously ascertained. 



Thus, two magnetic bars being selected, whose inductive 

 powers were as two to one, they were placed in succession im- 

 mediately under the suspended iron x, as in Fig. 1, but in such 

 way that their respective distances from x should, as in Fig. 16, 

 be inversely proportional to their powers of induction, the stronger 

 magnet 2m being placed at double the distance ; hence the want 

 of power in the weaker bar m was compensated by its diminished 

 distance a b (19) ; so that the force induced in x was in each ar- 

 rangement the same ; the forces, however, marked by the index 

 were inversely proportional to the distances ab and cd*. 



* Although this result, as disconnected with the previous investigations concern- 

 ing induced magnetism, it may be readily imagined, must happen, admitting the 



