78 PROCEEDINGS OF THE AMERICAN ACADEMY 



One is necessarily shut up to the two only possible ways of varying 

 the current ; namely, varying the resistance, or varying the electro- 

 motive force. I had tried the first with no satisfactory results, and 

 then attempted the second. 



In the spring of 1864, while a student in the Ohio Wesleyan Uni- 

 versity at Delaware, Ohio, I was employed to make a large electro- 

 magnet and a large permanent magnet for illustrative purposes at the 

 University. While engaged in making these, I devised a magneto- 

 electric telegraph, in which the currents were to be generated by a 

 permanent magnet thrust into a coil or hollow helix ; and these cur- 

 rents were to reproduce like motions upon a permanent magnet at the 

 other end of the line. The device was not dissimilar to the one made 

 by Gauss and Weber of Gottingen, in 1833 ; but I knew nothing of 

 their work at that time. 



In 1873 I observed a deflection of a galvanometer needle, when the 

 stem of a vibrating tuning-fork was held upon the face of a thermopile. 

 The tuning-fork used was a rather large one, giving E h of about 78 

 vibrations per second ; the prongs had been made magnetic for other 

 experiments, and the inductive effects of the movements of these poles 

 upon the face of the pile was also noted. The following is the record 

 from my note-book, and dated Aug. 15, 1873 : — 



" Noticed the effect of the vibrating fork, which was also a per- 

 manent magnet, upon the current, when one face of the pile was 

 heated. If the fork was moved no faster than the galvanometer 

 needle would vibrate, once in about 4 seconds, the needle would be set 

 swinging. If the fork vibrates its natural rate, 78 per second, the 

 needle couldn't move, as the current was changed faster than the 

 needle could move." 



This was a vibratory current in a closed circuit originated by sound 

 vibrations. 



I understood this to be simply a particular case of magnetic induc- 

 tion that was familiar enough to every one who was acquainted with 

 Faraday's work ; the former experiment I described at the Portland 

 meeting of the A. A. A. S., in 1873, as I thought it to be new. With 

 this experiment, and my invention of 1864, I was prepared with all 

 that was necessary for the plan for a speaking telephone, which was 

 matured and bears the date of Sept. 20, 1876. 



" Let a coil of wire be about the pole of a permanent magnet, and 

 the terminals be attached to a galvanometer ; then, when a piece of 

 iron approaches the magnet, a current is induced. Suppose that the 

 wires connect with another coil about a permanent magnet ; then the 





