THE TELEPHONE. l8/ 



first instrument was of a most primitive nature ; subsequently he produced 

 an instrument of which fig. 188 is the Telephone, fig. 189 the "receiver." 



In fig. 1 8 8, it will be seen that there is an aperture on the top and one 

 at the side; the latter is the mouthpiece. The top aperture is covered with 

 a membrane which is stretched very tightly. When a person speaks or sings 

 into the mouthpiece his voice is at once concentrated upon the tight 

 membrane, which it causes to vibrate in a manner corresponding with the 

 vibrations of the voice. There are two binding screws, one at each side. 

 To the centre of the tight membrane a piece of platinum is fixed, and this 

 is connected with the binding screw on one side, in which a wire from the 

 battery is fixed. On the membrane is a tripod, the feet of which (two) rest 

 in metal cups, one of them being in a mercury cup connected with the 

 binding screw at the opposite side to that already mentioned. The third 



Fig. 190. Bell's first Telephone (Transmitter). 



a. Electro-magnet b. Diaphragm, c. Collar, d. Collar and tube. f. Screw, g. Mouthpiece, h. Battery, 

 i. Wire from battery to coil k. Telegraph wire. /. Through binding screw, m. Pillar holding magnet. 



-'foot" a platinum point is on the platinum in the centre of the 

 membrane or top, and moves with it. Every time the membrane is 

 stretched by a vibration the platinum point is touched, and the closed circuit 

 is broken by the return of each vibration. 



The receiving instrument (fig. 189) consists of a coil enclosing an iron 

 rod, and fixed upon a hollow sounding box. It is founded upon a fact 

 discovered by Professor Henry, that iron bars when magnetized by an 

 electric current become a little longer, and at the interruption of the current 

 resume their former length. Thus in the receiver the iron will become 

 alternately longer and shorter in accordance with the vibrations of the 

 membrane in the box far away, and so the longitudinal vibrations of the bar 

 of iron will be communicated to the sounding box, and become perfectly 

 audible. This instrument, however, could only produce the "pitch" of sound, 

 "not different degrees of intensity, or other qualities of tones." It merely sang 



