1855.] P'Tof, Tyndall on Magnetic Repulsion. 13 



vious condition when the earth is in place, I can conceive, con- 

 sistently, as I think, with the conservation of force : and I think 

 the case is that which Newton looked at in gravity ; is, in 

 philosophical respects, the same as that admitted by all in regard to 

 light, heat, and radiant phenomena ; and (in a sense even more 

 general and extensive) is that now driven upon our attention in an 

 especially forcible and instructive manner, by the phenomena of 

 electricity and magnetism, because of their dependence on dual 

 forms of power. 



Jan. 22, 1855. [M. F.] 



WEEKLY EVENING MEETING, 



Friday, January 26. 



William Robert Grove, Esq. M.A. Q.C. F.R.S. 

 Vice-President, in the Chair. 



Professor Tyndall, F.R.S. 



On the Nature of the Force by which Bodies are Repelled from 

 the Poles of a Magnet. 



The Lecturer commenced, by showing that bodies are repelled by 

 the poles of a magnet, in virtue of a state of excitement into which 

 they are thrown by the latter. The repulsion of bismuth, and the 

 attraction of soft iron, followed precisely the same laws when the 

 strength of the influencing magnet was augmented, the respective 

 forces being pronortional, not simply to the strength, but within 

 wide limits, to tne square of the strength of the magnet. The 

 result is explained in the case of iron by the fact of its being con- 

 verted, while under magnetic influence, into a true temporary 

 magnet, whose power varies with that of the influencing one ,- and 

 in the case of bismuth, the result can only be explained by the fact 

 that the dia-magnetic mass is converted into a true dia-magnet. 



It was next shown that the condition of excitement evoked by 

 a magnetic pole was not the same as that evoked by another pole 

 of an opposite quality. If the repulsion were independent of the 

 quality of the pole, then two poles of unlike names ought to repel 

 the bismuth, when brought to act upon it simultaneously. This 

 is not the case. Two poles of the same name produce repul- 

 sion ; but when they are of equal powers and opposite names, the 

 condition excited by one of them is neutralized by the other, and 

 no repulsion follows. 



Bars of magnetic and dia-magnetic bodies were next submitted 



