SKETCH OF THOMAS ALVA EDISON. 491 



of electricity that is, whose resistance to a current would vary with 

 pressure. He began at one end of his stock of chemicals and tried 

 every one of them some two thousand but met with no satisfactory 

 result. Finally, when everything was exhausted, and he was looking 

 around for what next to try, an assistant brought him a piece of broken 

 lamp-chimney with an incrustation of lampblack : this was scraped off, 

 pressed into a little cake, and tried. He had at last discovered what 

 he was in search of. By placing it between two plates of metal con- 

 nected with the opposite poles of the battery, and making one of the 

 plates large, to receive the force of sound-waves, this varying pressure 

 would make the carbon cake more or less elastic to the passage of the 

 current of electricity, and the invention of the transmitting part of a 

 new telephone all his own was complete. For the receiving part 

 nothing was necessary but an ordinary electro-magnet with a dia- 

 phragm. Experiments with this "carbon telephone," as it is called, 

 are unfolding every day its marvelous sensitiveness, as shown in its 

 microphonic manifestations, which have been exciting so much won- 

 der. No less successfully is it being brought to measure the pressure 

 caused by infinitesimal heat for instance, that received by us from the 

 stars. 



Coming, lastly, to the phonograph : while experimenting on an auto- 

 matic transmitter in the early part of last winter, Mr. Edison tried tin- 

 foil, instead of paper, to receive the indentations of the Morse recorder, 

 and was surprised to see how readily it received them. These indenta- 

 tions, passing under another needle, were to repeat the message auto- 

 matically to another wire. A few days after, while handling a tele- 

 phone, the fancy seized him to fix a needle-point to a diaphragm, and 

 see whether the vibration of the diaphragm when spoken against would 

 cause the needle to prick his finger. It did. Then he wondered what 

 sort of an indentation this would make in a slip of paper. He tried it, 

 and, sure enough, there was the semblance of an indented track ! What 

 would be the effect of drawing this slip under the point again, following 

 the working of the automatic transmitter ? He tried that, and the re- 

 sult was one which almost made him wild. A sound like the stifled cry 

 of words seeking birth came from the diaphragm. No sleep or food 

 until he had made a grooved cylinder, put a piece of tin-foil instead of 

 paper on it, attached the diaphragm, and shouted into it, when, upon 

 turning the crank, the words came back with a marvelous elocution, 

 and the phonograph was a success. 



Mr. Edison has recently received the honorary title of Ph. D. from 

 Union College. 



