ClipArt ETC
"Nichols Rheostat. a, wooden frame; b, tinned iron strip; c, stationary, and c', movable binding-posts; d, copper strip for short-circuiting." -Whitney, 1911

Rheostat

"Nichols Rheostat. a, wooden frame; b, tinned iron strip; c, stationary, and c', movable binding-posts;…

This telephone uses magnets that converts sound into electrical signals to be transmitted over distances and then converts the signals back.

First Uses of the Telephone

This telephone uses magnets that converts sound into electrical signals to be transmitted over distances…