Siemens telegraph receiver, 1862.
© Science Museum / Science & Society Picture Library
This receiver printed the dots and dashes of Morse code onto paper tape. The telegraph's electric current would energise the receiver's twin electromagnets, which in turn attracted an iron bar operating a system of levers. It was these levers that forced the paper tape against an inking wheel, thus producing the code. A small flow of current made a short line or 'dot'; whereas a current 3 times as long made the 'dash'. However, the machine needed trained operators to decode the mesages.