the Laws of Magnetic Forces. 295 



28. As the iron be, Fig. 5, receives a magnetic developement 

 inversely proportional to its distance from the magnet m, we 

 may consequently, by varying this distance, alter the relative 

 magnetic intensity of b c at pleasure ; and thus, by fixing a se- 

 cond mass of iron de, Fig. 12, immediately above be, at a con- 

 stant distance eb, this mass de can be caused to operate on the 

 suspended cylinder #, by a sort of second induction ; so that, 

 by preserving the distances nd and eb, and at the same time va- 

 rying the distance ca, we have all the conditions required for de- 

 termining the law of the inductive influence, when the force of 

 a magnet be, Fig. 12, is made to vary, but its distance from the 

 iron de preserved constant. The experiment being thus ar- 

 ranged, it was found, as might have been previously anticipated, 

 that the second mass of iron de received an attractive force di- 

 rectly proportionate to the magnetic intensity of the mass be be- 

 low. 



The same result was obtained when, instead of varying the 

 magnetic force by induction, it was varied by means of magnets, 

 whose forces were to each other in a known ratio, applied suc- 

 cessively, at a constant distance cd, under the iron be, Fig. 5. 



The following Table contains the results of these experiments, 

 in which F signifies the relative magnetic intensities ; /the cor- 

 responding force of induction ; the distance dn, Fig. 12, and a b, 

 Fig. 5, at which it operated on the suspended cylinder x, being 

 two-tenths of an inch; as also the distance eb, Fig. 12. The 

 distance c d, Fig. 5, in which the induced force in b c was varied 

 by magnets, being made constantly equal to half an inch, each 

 > of attraction, being in both cases equal to one grain. 



