By WM. LANT CARPENTER, B.A., B.Sc, F.C S. 



Read October J^th, 1877. 



IN order to understand this wonderful little instrument— by 

 which, speaking in general terms, sound is converted into 

 electricity which travels along an ordinary conducting wire and is 

 reconverted into sound at the receiving end, so that speech is 

 possible between two points many miles apart — a clear under- 

 standing of certain acoustical and electrical facts, and of their 

 bearing upon each other, is necessary. I therefore propose to 

 remind you of some of these before proceeding to describe and 

 explain the mode of action of the telephone itself. 



And first, with regard to sound. It is well known, and may 

 be readily proved experimentally, that sound travels through the 

 air at a rate somewhat exceeding 1,100 feet per second, the exact 

 velocity increasing with a rise in the temperature of the air. In 

 water, the velocity is about four times greater ; in steel, sixteen 

 times ; and in pinewood, ten times. The transmission of sound 

 through rods of wood was shown more than twenty years ago by 

 a Telephonic Concert at the Royal Polytechnic, in London. Four 

 musical instruments were placed in the basement of the building, and 



