The Telephone continue....

The telephone also worked by transmitter of a telephone serves as a sensitive "electric ear." It lies behind the mouthpiece of the phone. Like the human ear, the transmitter has an 14 eardrum." The ear drum of the telephone is a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound waves strike the diaphragm and make it vibrate. The diaphragm vibrates at various speeds, depending on the variations in air pressure caused by the varying tones of the speaker's voice.