INTENSITY OF MAGNETIC AND DI AM AGNETIC FORCES. 751 



If, in the above determinations, a weight of 0-60 grm. had 

 been placed in that scale-pan which receives the weights for the 

 separation, the brass cup containing the bismuth would be re- 

 pelled by the electro-magnet in the first and third determinations, 

 but attracted in the second. 



57. In the sixth paragraph of my memoir of the 8th of Sep- 

 tember, I have drawn the conclusion on theoretical grounds, that 

 hy the admixture of two substances, one of which is magnetic, the 

 other diamagnetic, toe cannot procure a body which is absolutely 

 indifferent to the magnet. I was then only enabled to attribute 

 this to a body, which is inditferent at a given distance, be- 

 coming diamagnetic on the diminution of the distance, and mag- 

 netic on its increase. This may now be extended to the effect 

 that the same body may under exactly the same general cir- 

 cumstances become magnetic under the influence of feeble mag- 

 netism, but when the magnetic force is increased, passing through 

 the indifferent state, it may become diamagnetic. A direct con- 

 firmation of this appeared to me desirable. I therefore took a 

 gramme of the crystals of protosulphate of iron which had re- 

 cently formed ; these I carefully dried, dissolved in 50 grms. of 

 distilled water, and filled the watch-glass, which had been used 

 in the determinations of intensity, with the solution. When the 

 electro-magnetism was excited by two cells, it was found, by the 

 method made use of in the former determinations, that the 

 watch-glass with its contents was somewhat more strongly 

 attracted than the empty watch-glass. But when tefi cells were 

 set in action, the reverse occurred. Thus the solution reacted 

 magnetically in the first case, and diamagnetically in the second. 



The watch-glass, with its cover and ring, was still too strongly 

 magnetic to give these kinds of determinations all the accuracy of 

 which they are susceptible. The above proximate determination 

 of the point of indifference is in general more accurate than the 

 corresponding one in the 42nd paragraph of my memoir of the 

 22nd of January 1848, because in the latter the evaporation of 

 the uncovered fluid, arising from its small quantity and great 

 extent of surface, interferes with the result. 



Faraday states that 48"6 grs. of crystals of the protosulphate 

 of iron are insufficient for the removal of the diamagnetism of 

 10 cubic inches of water. From this it is evident, placing the 

 weight of the English cubic inch of water at 250*46 grs., that 

 the proportion is as 1 : 52. 



3 E 2 



