86 PROCEEDINGS OF THE AMERICAN ACADEMY 



an inch square, and being in direct contact, or separated by water 

 acidulated ; solutions of various sorts, such as nitrate of silver, sulphate 

 of copper, and so on, — all of them being available for the purpose, all 

 of them enabling one to talk and be understood, when an ordinary 

 telephone was used as a receiver. Still further modifications were 

 tried, in which a short wire made fast to the middle of the vibrating 

 plate was covered with a thin coat of wax, except the square end ; 

 this placed opposite to another end of wire, and both incased in a 

 small rubber tube filled with mercury. Thus the approach and reces- 

 sion of the points caused by the vibrations of the plate would increase 

 and decrease the resistance in the mercury, while the latter was pre- 

 vented from bounding away by the pressure of the tube. 



In another, a strip of tin was soldered to the plate and bent at right 

 angles so as to project outwards, and the end cut to a point with 

 about ninety degrees included angle ; this point rested upon another 

 similar one by light contact, and the current was varied by the amount 

 of surface in contact. The surfaces were also amalgamated and 

 then tried. 



Pieces of wood were also screwed to the plate, and then it was satu- 

 rated with water, with acids, with metallic salts, and with precipitated 

 silver ; and in all these ways it was found possible to vary the current 

 sufficient to reproduce sounds, and with almost all of them words were 

 reproduced ; that is to say, they were speaking telephones. 



All of the above work was done previous to January 1, 1878. 



Since then, the chief work has been done with the modification of 

 the transmitter, in which the plate vibrated directly against a point ; 

 and the results have been of such a character that I have given a name 

 to the special form, calling it an Electrophone, — a name which I 

 think to be more appropriate even for the common telephone than the 

 name it bears, inasmuch as it is a real conversion of electric energy 

 into sound-vibrations that is effected. 



A series of experiments was undertaken to determine if possible 

 the best size for such an instrument, the thickness of the plate, battery 

 power needed, and so on ; and to this end I had made an instrument 

 which would admit of the use of a plate varying in size from an inch 

 or less, up to one three inches and a quarter in diameter. I also had a 

 micrometer screw attachment, by which the advancement or recession 

 to the ten thousandth of an inch could be made. Then plates of iron, 

 steel, copper, brass, zinc, lead, tin, plumbago, and graphite were tried, 

 each of a differing size and thickness. With several of these some 

 most excellent results were obtained; for instance, with a plate about 



