English: Crude carbon rod microphone invented by David Edwards Hughes in 1878. It consists of a carbon rod (A) suspended by its pointed ends vertically between two metal electrodes (C). Sound vibrations transmitted from the wooden back (B) to the carbon-steel contact causes varying pressure on the carbon granules, causing variation in the carbon's resistance. Edwards found that the device was very sensitive, he was able hear the sound of a fly walking on it, and named it "microphone". Edwards did not invent the microphone but experimented with a wide range of "microphonic" electrical contacts. With another type of contact he discovered he could detect electromagnetic waves from a spark, thus inventing a type of coherer.