20 Experimental Researches in Electricity. 



tangential, while all other forces acting at a distance are di- 

 rect. Hence, if a magnetic pole on one side of a revolving 

 plate, followed its course by reason of its obedience to the 

 tangential force exerted upon it by the very current of elec- 

 tricity, which it has itself caused, a similar pole on the oppo- 

 site side of the plate would immediately set it free from this 

 force ; for the currents which tend to be formed by the ac- 

 tion of the two poles are in opposite directions ; or rather 

 no current tends to be formed, or no magnetic curves are in- 

 tersected, and therefore the magnet should remain at rest. 

 On the contrary, if the action of a north magnetic pole were 

 to produce a southness in the nearest part of the copper 

 plate, and a diffuse northness elsewhere, as is really the case 

 with iron ; then the use of a north pole on the opposite side 

 of the same part of the plate should double the effect, 

 instead of destroying it, and double the tendency of the first 

 magnet to move with the plate. On submitting these 

 views to the test of experiment, the fullest evidence was ob- 

 tained that with iron, and other bodies admitting of ordina- 

 ry magnetic induction, opposite poles on opposite sides of 

 the edge of the plate neutralise each other's effect, whilst 

 similar poles exalt the action. But with copper and sub- 

 stances not sensible to ordinary magnetic impression, similar 

 poles on opposite sides of the plate neutralise each other ; 

 opposite poles exalt the action, and a single pole at the edge 

 or end does nothing." "■ Nothing," Faraday concludes, " can 

 more completely shew the thorough independence of the ef- 

 fects obtained with metals by Arago, and those due to ordi- 

 nary magnet force ; and henceforth therefore the applicati- 

 on of two poles to various moving substances will, if they 

 appear at all magnetically affected, afford a proof of the na- 

 ture of that affection. If opposite poles produce a greater 

 effect than one pole, the result will be due to electric cur- 

 rent. If similar poles produce more effect than one, then 

 the power is not electrical ; it is not like that active in the 



