Experimental Researches in Electricity, 11 



to the development of this current, since while it remained 

 at rest, no deflection of the needle occurred ; and with refer- 

 ence to the relation of the current of electricity produced 

 to the magnetic pole, and to the direction of rotation of the 

 plate Mr. Faraday remarks that (( it may be expressed by 

 saying that when the unmarked pole (or that pointing to the 

 south pole of the earth) is beneath the edge of the plate, 

 and the latter revolves horizontally, screw-fashion, the elec- 

 tricity that can be collected at the edge of the plate nearest 

 the pole is positive ;" while that collected at the centre and 

 neighbouring parts is negative. The currents in the plate 

 are therefore from the centre by the magnetic pole to the 

 circumference. Hence then it appears that the case of the 

 copper disc is only an extension of that formerly noticed, 

 wherein a single piece of metal had currents of electricity 

 developed in it, at right angles as to the direction of the 

 motion, and crossing it at the place of the magnetic pole, or 

 poles between which it was made to move. For if we con- 

 ceive this wire to be moved in front of the magnet, like 

 the spoke of a wheel, a current of electricity tends to 

 flow through it from one end to the other; and as a solid 

 disc is made up of an infinite number of such spokes 

 or radii in contact, the currents will tend to flow in the 

 direction of these permanently, if a channel be open for 

 their return, which, in a continuous plate, is afforded by 

 the lateral portions on each side of the particular radius 

 near the magnetic pole. The existence of electrical currents 

 being thus the sole cause of the magnetism of rotation, it 

 is at once apparent why all effects cease when motion ceases, 

 since the currents have then no existence ; and it will be 

 found that, on applying the same principle of explanation to 

 the various results obtained by Messrs. Arago, Ampere, 

 Babbage, Herschell, and Harris, the most harmonious and 

 explicit results are obtained. 



The rapidity and facility with which Faraday appears to 



