DEVELOPMENT OF THE TELEPHONE 



down in history as the inventor of the first practical 

 instrument of this kind. 



PRACTICAL IMPROVEMENTS 



After Bell's invention became known a host of similar 

 inventions were made. None of these differed in prin- 

 ciple, however, from the original telephone invented 

 by Bell. A great number of improvements were made 

 both in the transmitter and receiver of the instrument, 

 but these were purely improvements upon the mechani- 

 cal application of the principles involved, and not depar- 

 tures from the principle itself. 



A great improvement upon the type of receiver was 

 made by Thomas A. Edison; and in 1877 Emil Ber- 

 liner invented what is known as a microphone trans- 

 mitter an apparatus which converts feeble sounds 

 into much louder sounds. By the addition of these two 

 inventions the telephone was greatly improved, and 

 sending and receiving messages at long distance became 

 possible. 



Berliner's microphone transmitter consists of a dia- 

 phragm with a metal patch in the centre. Against this 

 a metal knob is pressed lightly by an adjusting-screw, 

 the result of this arrangement being an apparatus which 

 greatly magnified the sound effects. 



Three months after Berliner produced his microphone 

 transmitter, another instrument designed for a similar 

 purpose was invented by Edison. This consists of a dia- 

 phragm having a platinum patch in the centre for an 

 electrode. Against this a hard point, m?de of plumbago 



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