THE TELEPHONE. 



appraaflhee the oore at ita bobbin it produces a current in the circuit, which 

 ha* alrr to circulate round the bobbin of the receiver, and thus the core of the 

 M .TrJuntf more or leas magnetic, and attracts its tin plate with greater 

 ^ fam. Thus the tin plate of the receiver reproduces on a smaller 

 but with perfect fidelity, every motion of the tin plate of the transmitter. 

 Thia perfect symmetry of the whole apparatus the wire in the middle, 

 the two telephone* at the end of the wire, and the two gossips at the ends 

 of the telephone* may be very fascinating to a mere mathematician, but it 

 would not satisfy an evolutionist of the Spencerian type, who would consider 

 anything with both ends alike to be an organism of a very low type, which 

 BM 4 hare ita functions differentiated before any satisfactory integration can 

 Uke place. 



Accordingly, many attempts have been made, by differentiating the function 

 of the transmitter from that of the receiver, to overcome the principal limitation 

 to the power of the telephone. As long as the human voice is the sole motive 

 power of the apparatus it is manifest that what is heard at one end must 

 be fainter than what is spoken at the other. But if the vibration set up by 

 the voice is used no longer as the source of energy, but merely as a means 

 of modulating the strength of a current produced by a voltaic battery, then 

 there will be no necessary limitation of the intensity of the resulting sound, 

 ao that what is whispered to the transmitter may be proclaimed ore rotunda 

 by the receiver. 



A result of this kind has already been obtained by Mr Edison by means 

 of * transmitter in which the sound vibrations produce a varying pressure on 

 a piece of carbon, which forms part of the electric circuit. The greater the 

 prwHure, the smaller is the resistance due to the insertion of the carbon, and 

 therefore the greater is the current in the circuit. 



I have not yet seen Mr Edison's transmitter, but the microphone of Prof. 



Hughes IB an application of carbon and other substances to the construction 



of a transmitter, which modulates the intensity of a battery current in more 



or leas complete accordance with the sound-vibrations it receives. The energy 



the aound produced is no longer limited by that of the original sound. All 



the original sound does is to draw supplies of energy from the battery, 



very feeble sound may give rise to a considerable effect. Thus, when 



a fly walks over the table of the microphone the sound of his tramp may be 



heard miles off 



