David Edward Hughes invented the carbon microphone
, which was essential to the development of the telephone
David Hughes (1831-1900) was born in London and grew up in the United States. He taught music and studied the science of sound at St. Joseph's College, Bardstown, Kentucky. In 1855, David Hughes received his first U.S. patent for a printer used with a telegraph instrument. In 1857, Hughes returned to London taking with him, his successful telegraph instrument that remained in common use until the 1930s.
David Hughes - Carbon Microphone
Invented in 1878, David Hughes's microphone was the early model for the various carbon microphones now in use. Hughes discovered that a loose contact in a circuit containing a battery and a telephone receiver created a situation where sounds in the receiver matched the vibrations upon the diaphragm of the telephone mouthpiece or transmitter
Hughes also invented the induction balance, often used as a type of metal detector, and researched the theory of magnetism.