Mr. Sturgeon on Electro-Magnetism. 245 



the equator EE to the pole P ; and descending in the lower 

 hemisphere hh from the equator to the mercury in the lower 

 cell, which is the place of the other pole of the sphere. From 

 the poles it is transmitted to the mercury in the upper cell eee, 

 by the conducting wires ww and ff\ and both circuits are 

 completed by the wires from the zinc cylinder terminating in 

 this cell. Thus two galvanic circuits are formed by one ap- 

 paratus ; and hence likewise is solved the apparent anomalous 

 phenomena of galvanized wires or cylinders rotating in dif- 

 ferent directions on the opposite poles of a magnet. This 

 delusive appearance is completely relative, and similar to our 

 notions of up and down : but with respect to the magnet, and 

 in reality, the rotation is the same on both poles : for exam- 

 ple, let any person turn first towards the north, and then 

 towards the south ; by observing the heavenly bodies, they 

 would appear to revolve to the left in the former, and to the 

 right in the latter case; yet the rotative motion of the earth 

 (which is the cause of their apparent motion) is constantly 

 the same way. In this experiment both poles of the magnet 

 are acted on at the same time by similar galvanized wires, and 

 the machine rotates by the joint influence of the former on the 

 excited wires of the latter. Owing, however, to the weight and 

 size of the machine, the rotation is but slow at the beginning 

 of the experiment, but soon acquires considerable velocity, and 

 the momentum, added to the generating force, keeps it in mo- 

 tion for a length of time. 



Well aware of the difficulties that would arise at the pre- 

 sentday in any endeavour to support an hypothesis of the earth's 

 being hollow, and containing within it a spherical magnet, as 

 was the opinion of Dr. Halley, I have confined myself to a de- 

 tail of the experiment only, without obtruding either remark 

 or opinion. The success of this experiment, however, so sa- 

 tisfactorily confirmed my expectations that the principle upon 

 which it was made could hardly fail to intimate its applicabi- 

 lity to others of a like nature; one of which being intimately 

 connected with the one I have just described, this may per- 

 haps be considered no improper place for its detail. 



The experiment for rotating the magnet on its axis, it is 

 well known, was first made by M. Ampere ; but the manner in 

 which as yet it has been exhibited, like all the other similar ex- 

 periments, shows the action on one half only of the magnet at 

 one time; — and by reversing the poles (every thing else re- 

 maining as before) it appears to rotate in a contrary direction. 



I hope, however, that I have satisfactorily proved that this 

 apparent contrariety of rotation is merely relative, and that 

 the real motion is the same in both cases. If possible, how- 

 ever. 



