Experiments with telephone diaphragms

It is well known that when the receiver of a telephone circuit is placed face to face with the transmitting microphone, continuous oscillation may be set up, and the telephone “howls,” i. e, a continuous note of definite pitch is heard. Experiments suggested by this phenomenon have been carried out by Prof. J., T. MacGregor-Morris and Prof. E. Mallett, and are recorded in the Journal of the Institution of Electrical Engineers.