Strange as it may seem, the actual sound of the voice does not travel over the telephone wire.
If a person looked into the old telephones from 1915
"a glance into the mouthpiece of the transmitter and into the ear-hole of the receiver will show a thin sheet of dark shiny metal."
This disk of metal is the ear-drum of the telephone.
When the sound waves of the voice strike this and enter the transmitter, they become electrical waves and flow silently over the wire until they reach the receiver at the other end. In the receiver the electrical waves again become sound waves and the listener hears the words of the person speaking.
source- Young American Readers: Community Interest and Public Spirit published 1919
