12 Experimental Researches in Ele&tricity, 



have apprehended the law of magneto-electric induction is 

 very remarkable, and indicates forcibly the clearness of his 

 conceptions of the relations of forces in space ; since by com- 

 mon consent of all who have turned their attention to the 

 subject, the law in question is exceedingly difficult to seize 

 at once, from the complicated manner in which electrical and 

 magnetic forces are related, the one set being at right an- 

 gles to the other. No such difficulty however seems to have 

 impeded Faraday's course ; for he remarks, " the relation 

 which holds between the magnetic pole, the moving wire or 

 metal, and the direction of the current evolved, i. e. the law 

 which governs the evolution of electricity by magneto-electric 

 induction is very simple, although rather difficult to express. 

 He then represents it by referring position and motion to the 

 curves that pass from one magnetic pole to another, as indi- 

 cated by the manner in which small iron filings arrange 

 themselves, when strewed upon a sheet of paper placed 

 over a magnet. te The current of electricity/' he states, 

 ec which is excited in a metal, when moving in the neigh- 

 bourhood of a magnet, depends for its direction alto- 

 gether upon the relations of the metal to the resultant 

 of magnetic action, or to the magnetic curves, and may 

 be expressed in a popular way thus : Let A B (see 

 figure) represent a cylinder magnet, 

 A being the marked pole, and B the 

 unmarked pole. Let P N be a sil- 

 ver knife-blade, resting across the 

 magnet with its edge upwards, and 

 with its marked or notched side 

 towards the pole A ; then in what- 

 ever direction or position this knife 

 be moved, edge-fore-most, either about the marked or 

 the unmarked pole, the current of electricity produced 

 will be from P to N, provided the intersected curves 

 proceeding from A abut upon the notched surface of 



