14 Experimental Researches in Electricity. 



ately the needle was deflected, so as ultimately to describe 

 arcs of no less than 150° or 160°! This, and other results, 

 led Faraday to hope that the direct inductive effect of the 

 earth's magnetism might be exhibited without the aid of 

 iron, and he accordingly found that by using merely the cop- 

 per helix above alluded to, and inverting it several times in 

 the line of dip, the galvanometer needle could be made to 

 vibrate through arcs of 80° or 90°. e< Here, therefore," he 

 infers, " currents of electricity were produced by the direct 

 inductive power of the earth's magnetism, and without the 

 use of any ferruginous matter, and upon a metal not 

 capable of exhibiting any of the ordinary magnetic phe- 

 nomena." 



Passing now to the subject of the magnetism of rotation, 

 it was found that all the phenomena of the revolving copper- 

 plate could be exhibited without the use of any other 

 magnet, than the earth. Upon rotating this plate in a 

 horizontal plane, which in the latitude of London, where 

 the experiments were made, would be inclined about 7° 

 to the line of dip, the needle was immediately deflect- 

 ed, while, in perfect accordance with the law of mag- 

 neto-electric induction, if this rotation took place in the 

 plane of dip, then no effects were produced upon the gal- 

 vanometer, since the magnetic curves were not in this case 

 intersected, and without such intersection electrical currents 

 could not be developed. The moment however the in- 

 clination of even a few degrees to the plane of dip was 

 given to the plane of the plate's rotation, then electricity 

 made its appearance, and became more and more powerful, 

 till the inclination reached 90°, when for a given velocity it 

 was a maximum. " It is a striking thing, " says Faraday, " to 

 observe the revolving copper plate become thus a new elec- 

 trical machine; and curious results arise on comparing it 

 with the common machine. In the one, the plate is the best 

 non-conducting substance that can be applied ; in the other, 



