OP ARTS AND SCIENCES. 81 



or relay, could be made to vibrate by sound-vibrations, the corre- 

 sponding armature of another like instrument in the circuit should 

 respond to the induced current. The armature of an ordinary sounder 

 was first screwed down pretty near to the poles of the magnet, and 

 then the thread from a common string telephone was tied to it, so that 

 the sounds produced in the string telephone should be conveyed by 

 the string to the armature, and thus make it to vibrate. This arrange- 

 ment was coupled up in electric circuit with a telephone of ordinary 

 pattern, and tried between two distant rooms in a building, with success. 

 Afterwards two like sounders were thus coupled up, and talking was 

 carried on over a circuit nearly half a mile long, using only the 

 sounders with the thread telephone tied to each. The sounders had a 

 resistance of only two or three ohms apiece. Then two relays were tried 

 in like manner, each relay having nearly a hundred ohms resistance, 

 with better results than before. At one time the thread telephone 

 attachment was dispensed with, and the vocal sounds were produced 

 in a small tube held immediately in front of the relay armatures both 

 at sending and receiving instruments. In this way it was easy to hear 

 musical sounds, such as a tune sung ; and sentences, if at all familiar, 

 were recognized without much difficulty. But this was of course 

 working under a great disadvantage. I therefore devised a mouth-piece 

 for the armature, and afterwards changed the form of the armature 

 itself, so that it would be adapted to both functions, — that of an ordinary 

 sounder and of a speaking telephone. With such an instrument as I 

 exhibit here, I have worked successfully over the line between Milford, 

 N. H., and Boston, — a distance of fifty miles. 



From the first I had interpreted the action of the telephone to be 

 due solely to the ordinary vibrations of the plate being performed in 

 a magnetic field, and varying that field of magnetism. When an ordi- 

 nary tuning-fork is struck, its vibrations may not only be heard but 

 felt, and also seen ; but directly the amplitude decreases, so that it 

 cannot be seen to vibrate, but it can be both felt and heard : but long 

 after it cannot be felt it may still be heard. But no one is at liberty to 

 say that, because the sound only can be heard, the vibrations of the fork 

 differ in any thing than amplitude from those at first seen ; and it 

 is admitted generally that such vibrations would be competent to pro- 

 duce such sonorous results as are observed. Nevertheless, there 

 have been several investigators who have stated it as their opinion 

 that the sounds of the telephone were due to some new kind 

 of molecular motion, which was different from an ordinary sound- 

 vibration. To test this view, I constructed a telephone having a mem- 

 vol. xiv. (n. s. vi.) 6 



