. Bulletin. Science. Figure 76.—Patent drawing of Runnings' carbon granule telephone transmitter. From patent 246512 (August 30, 1881). ther refined his approach by basing his experimenta- tion upon the fact that the apparent resistance of semi- conductors varied considerably with the pressure, and a few months later he created a successful transmitter. (See figs. 71, 72.) Edison filed the applications for the patents''^ on the first of his many forms of the carbon transmitter on April 1 and 27 and July 20, 1877. Basically Edison's transmitter consisted of a mass of carbon in various shap
. Bulletin. Science. Figure 76.—Patent drawing of Runnings' carbon granule telephone transmitter. From patent 246512 (August 30, 1881). ther refined his approach by basing his experimenta- tion upon the fact that the apparent resistance of semi- conductors varied considerably with the pressure, and a few months later he created a successful transmitter. (See figs. 71, 72.) Edison filed the applications for the patents''^ on the first of his many forms of the carbon transmitter on April 1 and 27 and July 20, 1877. Basically Edison's transmitter consisted of a mass of carbon in various shapes and textures, against which a vibrat- ing diaphram pressed. Change of pressure on the diaphram brought a change of resistance of the car- bon and so modulated the current. Edison's device soon proved to be better than Bell's magneto trans- mitter; and although it was insensitive by modern standards, shouting was no longer mandatory in order to carry on a telephone conversation. The Edison transmitter was rugged, and it gave a better quality of reproduction than Bell's Figure 77.—Diagram of White's "solid-back" telephone transmitter. Reprinted (with per- mission) from F. Rhodes, Beginnings of Telephony, Harper and Brothers, New York, 1929, p. 81. In England the carbon transmitter was suggested independently by David Hughes in 1878.*^ Hughes revived the term "microphone" to describe his var- iable contact transmitter with its remarkable sensi- tivity. Hughes' microphone (fig. 73) was constructed of several pieces of carbon that rested loosely on or against one another. This whole mass of carbon was mounted on a sounding box. When Hughes announced his discovery, he disclaimed any inten- tion of taking out a patent because his laboratory model, although as sensitive as it was simple, was too erratic in performance to be practical. In America applications for patents on other mod- ulating transmitters were submitted, and it was soon found that
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