CHAP, xii.] ELECTRICITY AND MAGNETISM. 409 



the same substance fixed to a sounding-board of thin 

 pine-wood, the blocks being connected with one or two 

 small cells and a Bell telephone as a receiver. The 

 amplitude of the vibrations emitted by this telephone 

 may be much greater than those of the original sounds, 

 and therefore the microphone may serve, as its name 



Fig. 167. 

 p 



' indicates, to magnify minute sounds, such as the ticking 

 of a watch or the footfalls of an insect, and render them 

 audible. The less sensitive carbon -transmitters, used 

 frequently in conjunction with the telephone, are some- 

 times regarded as varieties of the microphone. In these 

 instruments, however, the action more nearly resembles 

 that of Edison's carbon telephone. 



