UD I SON'S ACOUSTIC INVENTIONS. 



137 



shown in Fig, 25. It is like the ordinary magneto-telephone, except 

 that the circular diaphragm is replaced by a strip of thin iron, the 

 edges having been bent so as to render it stiff. We mention it, simply 

 because it demonstrates the fact that it is not essential that the dia- 

 phragm be circular. 



A novel and purely mechanical telephone is illustrated by Fig. 26. 

 In place of a line-wire, the illuminating gas, contained in gas-pipes, is 

 used. It is calculated for short distances only, as it is essential that 



A. 



-r' 



A. — ^ 



i 



Fig. 26. 



Fig. 27. 



Fig. 28. 



the gas used in communicating oflSces should be drawn from the same 

 main pipe. In the figure, Pis the main pipe. The telephones are rep- 

 resented at J' and T'. The instrument is merely a cone fastened by 

 its apex to the gas-pipe in place of the burner. The larger end is closed 

 by a thin circular diaphragm. The vibrations are conveyed from one 

 diaphragm to another through the medium of the gas. 



The phonograph and telephone, when combined, form an instrument 

 known as the telephonograph, of which Fig. 27 is a representation. 

 The drum of the phonograph is shown in section. The diaphragm, 

 instead of being vibrated by the voice, is vibrated by the currents 

 which traverse the helix, H, and which originate at a distant station. 

 The object of the instrument is to obtain a record of what is said 

 at the distant office, which can be converted into sound when de- 

 sired. 



The Motograph. — The motograph-receiver, from which we have 

 been accustomed to hear sounds almost destitute of quality, has, by 

 a little modification, become an articulating telephone. It works quite 

 well in conjunction with the Edison carbon-transmitter. In Fig. 28 the 

 back of the motograph-receiver has been removed, showing its con- 

 struction. Within the drum D is contained the decomposing solution, 



