198 Mr. Faraday, on certain Magnetic Actions. [Feb. 22, 



equal number of degrees. A piece of amorphous bismuth, com- 

 pressed in one direction, gave nearly the same amount and degree of 

 cliange for the same alteration of temperature ; leading us to the 

 persuasion that the whole magnetic force of bismuth as a diamag- 

 netic body would suffer like change. A crystal of tourmaline, which 

 at 0^ had a setting force of 540, when raised to 300°, had a setting 

 force of only 270 : the loss of force was progressive, being greater at 

 lower than at high temperatures ; for a change from Qp to SO'' caused 

 a loss of force equal 50, whilst a change from 270° to 300'=', caused a 

 loss of only 20. Carbonate of iron suffered a like change ; at 0^ the 

 force was 1140, at 300° it was only 415 ; at the lower temperature 

 the loss for ^0^ was 1 20 of force, at the upper it was only 34. 



In all these and in many other cases, both with paramagnetic 

 and diamagnetic bodies, the magne-crystallic differences diminished 

 with the elevation of temperature ; and therefore it may be con- 

 sidered probable, that the actual magnetic force changed in the same 

 direction. But on extending the results to iron, nickel, and cobalt, 

 employing these metals as very small prisms associated with copper 

 cubes to give them weight, it was found that another result occurred. 

 Iron, whether at the temperature of 30° or 300°, or any intermediate 

 degree, underwent no change of force, it remained at 300, which 

 was the expression for the piece employed under the circumstances. 

 We know that at higher temperatures it loses power, and that at a 

 bright red it is almost destitute of inductive magnetic force. A 

 piece of nickel, which at 95° had a setting power of 300, when 

 raised to 285°, had a power of only 290, so that it had lost a thirtieth 

 part of its force ; at the heat of boiling oil, it is known to lose 

 nearly all its force, being unable then to affect a magnetic needle. 

 Cobalt, on the other hand, requires a far higher temperature than 

 iron to remove its magnetic character, a heat near that of melting 

 copper being necessary. As to lower temperatures it was found, 

 that an elevation from 70° to 300° caused an absolute increase of 

 the magnetic force from 293 to 333. It is evident, therefore, that 

 there is a certain temperature, or range of temperature above 300°, 

 at which the magnetic force of cobalt is a maximum ; and that 

 elevation above, or depression below that temperature causes a 

 diminution of the force. The case is probably the same for iron ; 

 its maximum magnetic force occurring at temperatures between 0° 

 and 300°. If nickel is subject to the same conditions of a maximum? 

 then that state must come on at temperatures below 0' : and it may 

 be further remarked, that as the maximum conditions occur in the 

 following order for ascending temperatures, nickel, iron, cobalt, 

 such also is the same order for the temperatures at which they lose 

 their high and distinctive magnetic place amongst metals. 



[M. F.] 



