Experimental carbon pencil microphone, 1878-1890

Experimental microphone consisting of two carbon pencils having knife edges in contact, probably made by David Edward Hughes, England, 1878-1890.

The development of the microphone owes much to David Edward Hughes (1831-1901). Building on the work of Willoughby Smith and Sir William Thomson, Hughes attempted to detect changes in the resistance of wire with sound. He discovered that these changes occurred only when his stretched test wire broke and when he touched the ends together. He found that light but constant pressure was the only essential and that pieces of carbon in light contact worked best. Hughes did not patent his discoveries, meaning that subsequent inventors were able to make use of them without giving Hughes the credit.