OP ARTS AND SCIENCES. 79 



current will affect a piece of iron in front of the poles in the same way 

 as the first is affected. In this way a telephone may be constructed. 

 By making a sound to vibrate a piece of sheet iron in front of one 

 magnet, the ear applied to the other magnet should hear the kind of 

 sound made at the first." 



Within a few days of that time, I began the construction of a pair 

 of such instruments, entrusting them to Mr. A. Stetson, a teacher at 

 Rockland, who came to Tufts College on Saturdays to work in the 

 Physical Laboratory. The first ones attempted were begun with a 

 pair of straight-bar permanent magnets belonging to the College ; they 

 were 8 or 9 inches long and about half an inch in diameter. The 

 helix was wound directly upon the magnets, while the vibrating arma- 

 ture was glued to an opeidoscope membrane. The first one made I 

 have now, just as it was used at that time ; the membrane was made 

 of sheet rubber, and was two and three-eighth inches in diameter. 

 The iron armature glued to it was an inch and a half long by three 

 quarters of an inch broad, rectangular in outline. 



Mr. Stetson was employed to make a pair of instruments, in which 

 no battery was to be used, and both instruments were to be alike. 

 Before they were completed, he stopped coming to the College for 

 several weeks, and they were consequently delayed in a manner that 

 they would not have been if I had thought of the very great value 

 of the invention. 



I was extremely busy with my college work and also in getting a 

 book through the press, and couldn't attend to it very well myself. 

 About the first of October, the plan of using an armature of iron glued 

 to a membrane was changed to one where the armature was to cover 

 the entire end of the tube and be screwed to it. This was done for 

 two reasons ; one being that the armature could not be brought close to 

 the magnet without its adhering to it, and, second, that the vibrations 

 of the voice-sounds could be easily felt when talking against a large 

 piece of rigid paper or piece of board, from which it was inferred that 

 the vibrations of an iron armature would be sufficient to induce the 

 requisite currents. Mr. Stetson started a pair upon this plan at once, 

 but, as I said before, he failed to complete them, as he did not come to 

 College Hill from about the fourteenth of October till some time in De- 

 cember. Early in December, one evening, I took one of the incomplete 

 telephones and endeavored to measure the resistance through which 

 such an induced current would be manifest by means of a Thomson 

 galvanometer and a set of Resistance Coils, and found I could readily 

 get a deflection with an inserted resistance of fifteen thousand ohms, — 



