Mr. Sturgeon on Electro-Magnetism. 247 



public lectures, to be enabled to exhibit this experiment to the 

 satisfaction of a large audience ; for as the lecturer can now 

 have his rotating magnet of almost any size he pleases, and 

 likewise of any figure, this interesting experiment may be 

 viewed from the remotest part of the lecture-room. Another 

 inconvenience I have almost entirely removed both in making 

 this and every other electro-magnetic experiment. My bat- 

 teries are of such a peculiar construction as not to annoy 

 the experimenter by the escape of hydrogen ; neither is the 

 expense of making the experiments more than one-fortieth 

 of any other method yet made public ; yet the apparatus in 

 general is of large dimensions ; for instance, the sphere in 

 the former experiment is 9^ inches diameter; and the mag- 

 net in the latter is 8 inches long. 



I should now proceed to the description of other new ex- 

 periments, were I not confident that I have already intruded 

 upon your valuable pages. That task must therefore be de- 

 ferred for - the present. Some of the minor of those experi- 

 ments are, — The rotation of the cylinder by the influence of an 

 external magnet;— Ampere's cylinders rotated independent of 

 each other's weight ; — Thermo-rotation on both poles of the 

 magnet ; — Electro-magnetic bells, &c. 



In summing up the results of the two detailed experiments, 

 it appears from the first, — 



That similar electrized wires rotate in the same direction 

 round both poles of the magnet ; 



That both the copper and zinc cylinders are here carried 

 round the magnet in the same direction ; 



That a sphere conducting similar currents of electricity 

 from its equator to its poles, will rotate by the influence of an 

 internal magnet. 



And from the second it is evident that, had the magnet in 

 the first experiment been free to move, it would likewise have 

 rotated at the same time with the sphere containing it. This 

 property would seem somewhat conformable to the opinion 

 of Hal ley, who supposed the earth to contain a spherical mag- 

 net, which rotated within the shell that we inhabit. And, 

 what is more fortunate to the analogy, it is proved by the ex- 

 periments that when the electric currents are of the same kind 

 from the equator to the poles of both nucleus and shell, they 

 both rotate in the same direction. The rotation would like- 

 wise be as effectual were the magnetic poles removed to some 

 distance from the axis of motion. 



Another hypothesis might be advanced to account for the 

 rotatory motion of the earth, and which would not require the 

 supposition of it* being hollow: but onlv to be regarded as a 



grand 



