74 



Professor Barrett, 



different qualities of different voices are heard, so that at 50 or 

 100 miles distance the individuality of the speaker is transmitted 

 as well as his ideas. 



A section of the present form of this important instrument is 

 shown in figure 1. A diagrammatic representation of the essential 

 parts is given in figure 2 : a permanent bar magnet (N.S.) (about 

 four inches long), has a coil of fine wire (b) wound at one extremity, 

 in front of the coil a disc (a) of thin sheet iron is fixed. The 

 transmitting and receiving instruments are precisely alike, and no 

 further source of electricity is required than that produced by 



Fig. 1. 

 Section* 



Zinc/ 



