Chase.] 353 [April. 



other is counteracted by an equivalent and opposite centi'al energy of 

 elasticity. Therefore, when we compare the relative efiFects of rota- 

 tion and gravity, it is immaterial whether we use as the measure of 

 force, the integral of the vires vivae, or the respective amounts of 

 motion that the two forces would produce, if they were able to act 

 freely for the same time. The difficulty of determining the repul- 

 sion of molecular elasticity precluding any satisfactory use of the 

 former measure, I employed the other, and the precise accordance of 

 the results thus obtained, with the results of observation, justi6ed the 

 correctness of the hypothesis, in the same manner as the accurate 

 computation of planetary motions has confirmed the Newtonian theory 

 of gravity. 



Gravity, therefore, with the same propriety as heat, may be con- 

 sidered as a '' mode of motion," whether acting merely as "dead 

 weight," or as an accelerating or a deflecting force. If it can be 

 shown that magnetism also originates in motion, we may be able to 

 demonstrate the mutual convertibility that Faraday suspected. 



The earliest hypothesis with regard to terrestrial magnetism looked 

 for its cause to a powerful magnet, lying nearly in the line of the earth's 

 axis. Subsequent discoveries led to a modification of this view by the 

 supposition of another magnet, pointing towards the Siberian pole. Mr. 

 Barlow's idea, that the magnetism is superficial and induced,* has now 

 been generally adopted, and if it could be shown that solar or rotary 

 action is capable of developing magnetism in particles such as those 

 which are known to constitute our globe, the great difiiculty in the 

 way of a satisfactory explanation would be rembved.f Ampere's, 

 Barlow's, and Christie's experiments showed that simple rotation is 

 suQicient to affect the magnetism of a compass-needle,J and in the 

 oxygen of the atmosphere, which, as Faraday discovered, has a spe- 

 cific magnetism, variously estimated at from gg2§ to »^^\\ of that of 

 iron, we have a medium through which any induced magnetism may 

 be distributed over the entire surface of the earth. Some simple ex- 

 periments that can be easily repeated, seem to confirm Ampere's 

 views, and to indicate the manner in which the circulating electric 

 current is excited. 



* Phil. Trans., 1831. 



t Enc. Brit., Art. "Magnetism." 



I The effect of rotation on the magnetic needle may be shown in a rough way, 

 by causing an ordinary grindstone to revolve rapidly, and bringing a compass 

 near its edge. 



§ By M. Becquerel. || M. Pliicker. 



