lOb PHILOSOPHICAL J'KANSACTIONb. [aNNO 1725. 



Philosophers are agreed, that both poles of the magnet do not act with equal 

 force; but that the north poles are stronger than the south : tliis has been 

 asserted indeed, but no where accurately demonstrated : and because M. Mus- 

 chenbroeck's method of estimating the magnetic forces, was sufficiently easy, 

 and that this might be thus accurately determined; he turned both the poles of 

 each magnet in such a manner, that the corresponding poles might be opposite 

 to each other; the observations he made on the magnets in this last experiment, 

 were as follow : 



Hence it evidently appears, that both poles of the magnet do not act with 

 the same force ; the quantity of the difference may be seen by comparing both 

 these tables together. 



Since M. Muschenbroek had hitherto been persuaded, that the action of the 

 magnet depends on effluvia, or at least on some impelling fluid without the 

 magnet; and since he had observed, that the most learned i)hilosophers were of 

 the same opinion, he had a mind to try whether he could confirm this by any 

 experiment. While he made the former experiments with magnets, therefore, 

 placed at difi^erent distances from each other, he interposed very thick pieces of 

 lead, tin, silver, copper, and a pretty large mass of mefcury, in order to see 

 whether the magnetic effluvia would not be intercepted; and if not entirely, yet 

 if in some measure at least: glass is pellucid and transmits the rays of light, but 

 not in such quantity as with glass intervened ; in the same manner he supposed 

 that the magnetic effluvia, if they were not quite intercepted, yet in some de- 

 gree would hinder the magnets from attracting with such force, if a piece of 

 lead of a cubical foot, or a piece of lead 2 inches thick, the tin of the same 

 thickness, and afterwards copper or a large mass of mercury, intervened be- 

 tween them ; but he observed, that whatever bodies he interposed, the magnetic 

 forces were always the same, as if no such bodies at all intervened ; which he 

 thinks indeed a thing surprising and not to be understood : for we are not to 

 suppose that these bodies are so porous, as to have no solidity; if therefore they 

 have some solid parts, as they have a great deal, shall not these hinder the ap- 



