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BELL SYSTEM TECHNICAL JOURNAL 



The essential element of this device is what has come to be called 

 the "loose contact" — or, as its name implies, a contact between two 

 conductive solids, metals as well as carbons, held together with small 

 forces. The ability of "loose contacts" to transmit speech was 

 discovered independently by Emile Berliner in this country and 

 Professor D. E. Hughes in England. Following Hughes* discovery, 

 Mr. Spottiswood, the president of the British Association in 1878, 

 described it thus: "The microphone affords another instance of the 

 unexpected value of minute variations — in this case, electric currents; 

 and it is remarkable that the gist of the instrument seems to be in 

 obtaining and perfecting that which electricians have hitherto most 

 scrupulously avoided, viz., 'loose contacts.'" Hughes applied the 

 word "microphone" to his instrument because of its remarkable 

 "ability to magnify weak sounds." The word itself is a revival of a 

 term first introduced by Wheatstone in 1827 for a purely acoustical 

 device developed to amplify weak sounds. Although originally con- 

 fined to the "loose contact" type of instrument, the term microphone 

 has more recently been used — particularly in broadcast, public 

 address, and sound picture work — for any device which converts 

 sound into corresponding electric currents. 



Evolution of the Carbon Microphone 

 The story of the development of the "loose contact" type of micro- 

 phone is a fascinating one and, although it is beyond the scope of this 



LINE 



Fig. 1— Sketch, illustrating Bell's conception of the telephone, used in his first patent 



application of 1876. 



paper, 1 I should like to refer briefly to a few of the stages in the evo- 

 lution of the present day instrument. You will recall that Bell's 

 original telephone (Fig. 1) was electromagnetic in principle and acted 



' I'or a more complete account see paper by H. A. Frederick, "The Development 

 of the Microi)hone," Bell Telephone Quarterly, July, 1931. 



