Although the Bell telephone is both a transmitter and receiver, in practice a more sensitive and better form of transmitter has taken its place. That most generally used and best known is the “Blake transmitter,” which was brought out about 1880. This employs two important elements. The first is the carbon microphone, which is a means for producing the undulations in the current by the variations in pressure on carbon contacts, and the second is an induction coil operated by a local battery, whose primary circuit passes through the contacts of the carbon microphone, and whose secondary circuit passes over the line. These fundamental elements of the Blake transmitter were the inventions of Berliner and Edison, and were made in 1877. The broad idea of producing electric undulations by varying the pressure between electrodes by vocal vibrations, was a large bone of contention in the Patent Office between various inventors. An application for a patent for the same was filed in the Patent Office by Emile Berliner, June 4, 1877, which was contested in an interference by Gray, Edison, Richmond, Dolbear, Holcombe, Prof. Bell, and others. After fourteen years of litigation the patent was finally awarded to Berliner. The patent granted to him November 17, 1891, No. 463,569, is a valuable one, and has become the property of the American Bell Telephone Company. The application of a low resistance conductor (carbon) in a microphone was invented by Edison as early as 1877, but his patent, No. 474,230, did not issue until May 3, 1892, on account of the interference with Berliner on the broader principle. [Illustration: FIG. 59.--BLAKE TRANSMITTER.] [Illustration: FIG. 60.--DIAGRAM OF CIRCUITS IN BLAKE TRANSMITTER.]