233 Contributions to Electricity and Magnetism^. 



SECTION VI. 



2%e production of Induced Currents of the Different Orders 

 from Ordinary Electricity. 



98. Dr. Faraday, in the ninth series of his researches, remarks, 

 that " the effect produced at the commencement and the end of 

 a current (which are separated by an interval of time when that 

 current is supplied from a voltaic apparatus) must occur at the 

 same moment when a common electrical discharge is passed 

 through a long wire. Whether if it happen accurately at the 

 same moment, they would entirely neutralize each other, or 

 whether they would not still give some definite peculiarity to the 

 discharge, is a matter remaining to be examined." 



99. The discovery of the fact that the secondary current, 

 which exists but for a moment, could induce another current of 

 considerable energy, gave some indication that similar effects 

 might be produced by a discharge of ordinary electricity, provided 

 a sufficiently perfect insulation could be obtained. 



Fig. 11. 



a glass cylinder, h Leyden jar, c magnetizing spiral. 



100. To test this, a hollow glass cylinder, Fig. 11, of about 

 six inches in diameter, was prepared with a narrow riband of tin- 

 foil, about thirty feet long, pasted spirally around the outside, and 

 a similar riband of the same length, pasted on the inside ; so that 

 the corresponding spires of the two were directly opposite each 

 other. The ends of the inner spiral passed out of the cylinder 

 through a glass tube, to prevent all direct communication between 

 the two. When the ends of the inner riband were joined by the 

 magnetizing spiral (11,) containing a needle, and a discharge from 

 a half gallon jar sent through the outer riband, the needle was 



