98 On the Magnetism developed hy Rotation. 



in developing signs of magnetism were, copper, zinc, silver, 

 tin, lead, antimony, mercury', gold, bismuth, and carbon in 

 that peculiar metalloidal state in which it is precipitated from 

 carburetted hydrogen in gas works. In, the case of mercurj', 

 the rigorous absence of iron was secured. In other bodies, 

 such as sulphuric acid, rosin, glass, and other non-conductors, 

 or imperfect conductors of electricity, no positive evidence of 

 magnetism was obtained. 



The comparative intensities of action of these bodies were 

 next numerically determined by two different methods, viz., 

 by obser\-ing the deviation of the compass over revolving 

 plates of great size cast to one pattern, and by the times of ro- 

 tation of a neutralized system of magnets suspended over them; 

 and it is curious that the two methods, though they assigned 

 the same ordei to the remaining bodies, uniformly gave op- 

 posite results in the cases of zinc and copper, placing them 

 constantly above or below each other according to the mode 

 of observation employed. 



Our authors next investigated the effect of solution of con- 

 tinuity on the various metals: in the course of which M. Arago's 

 results of the diminution of effect by division of the metallic 

 plates used were verified ; and the further curious fact ascer- 

 tained, that re-establishing the metallic contact with other 

 metals restores the force, either wholly or in great measure ; 

 and that even when tlie metal used for soldering has, in itself, 

 but a very feeble magnetic power, thus affording a power of 

 magnif^nng weak degrees of magnetism. The law of diminu- 

 tion of the force by increase of distance was next investigated. 

 It appears to follow no constant progression according to a 

 fixed power of the distance, but to vary between the square 

 Jand the cube. 



The remainder of this paper was devoted to some able and 

 elaborate reasoning on the facts detailed. — The authors con- 

 ceive that they may be all explained without any new h3'po- 

 thesis in magnetism, by supposing simply that time is requisite 

 both for the development and loss of magnetism ; and that 

 different metals differ in respect, not only of the time they re- 

 quire, but in the inteusity of the force ultimately producible 

 in them; and they apply tliis explanation not only to their 

 own results, but to those obtained by Mr. Barlow in his paper 

 on the rotation of iron. 



Experiments on the Magnetism produced by Rotation. By 

 S. H. Chhistie, Esq., in a Letter to Mr. Herschel. 



Mr. Christie, in this communication, gave an accoimt of 

 some experiments on the development of magnetism in copper 



by 



