J. Trowbridge — A Telephone Relay. 34-5 



layer of air. In fact, the layer of separating air is incapable 

 of transmitting the feeble vibrations of a telephone diaphragm 

 sufficiently for relaying; while a suitable solid sound-trans- 

 mitting support to the microphone in contact with the edges 

 of a diaphragm actuated by the movements in the magnetic 

 field transmits such vibrations very efficiently. This is an 

 exemplification of the fact that a person partially deaf can 

 hear if the vibrations are conveyed to the ear by contact with 

 the supports of the ear. 



Considering thus the principles involved in the construction 

 of a practicable telephonic relay, I have invented the relay 





'V, 



described below ; a relay in which the barrier of undesirable 

 " growling or roaring " is obviated ; and a relay which per- 

 mits of the desirable separate adjustment of magnetic parts 

 and microphonic parts. 



The relay consists of a small coil with a laminated iron core, 

 which is balanced by two small diaphragms in a balanced mag- 

 netic field : the telephonic currents to be repeated or relayed 

 enter the little coil and disturb the magnetic balance in the 

 magnetic field. 



In fig. 1, NS (diagrammatic) represent the poles of the 

 magnetic field, C the moving coil actuated by the telephonic 

 currents to be relayed, A and B the supporting diaphragms, 

 DE sound-communicating support of the microphonic contacts 

 or transmitter. This can be a heavy disc : in some experi- 

 ments I have used a brass disc one half an inch thick and 



