Experimental Researches in Electricity, 13 



the knife, and those from B upon the unnotched side. 

 Or, if the knife be moved with its back foremost, the 

 current will be from N to P in every possible position 

 and direction, provided the intersected curves abut on the 

 same surfaces as before. A little model is easily construct- 

 ed, by using a cylinder of wood for the magnet, a flat piece 

 for the blade, and a piece of thread, connecting one end of 

 the cylinder with the other, and passing through a hole in 

 the blade, for the magnetic curves; this readily gives the 

 result of any possible direction." 



The results detailed in the section on magneto-electric 

 induction were obtained with equal facility by the employ- 

 ment of electro-dynamic cylinders instead of magnets, thus 

 affording additional experimental evidence in favour of 

 Ampere's beautiful and comprehensive theory, and all tend- 

 ing to prove " that the power of inducing electric currents is 

 circumferentially exerted by a magnetic resultant or axis of 

 power just as circumferential magnetism is dependent upon, 

 and is exhibited by, an electric current." 



Having discovered the law relative to direction according 

 to which magneto-electric induction took place, it became 

 immediately apparent that the earth itself might be substi- 

 tuted for the magnets employed in all the previous experi- 

 ments ; and accordingly in his second series of Experimental 

 Researches, Faraday investigates the subject of terrestrial 

 magneto-electric induction, and furnishes the most striking 

 instances of the production of electrical current, by the in- 

 fluence of the magnetism of the above. Having taken a 

 hollow copper helix, into which a cylinder of iron, first heat- 

 ed red hot, and then slowly cooled, to deprive it of all mag- 

 netism, was inserted ; he attached the wires of the helix to 

 those of a galvanometer, and holding the combined bar and 

 helix in the magnetic direction or line of dip, he merely 

 inverted them, so that the lower extremity became the upper, 

 the whole being still in the magnetic direction, and immedi- 



