Re: The Telegraph, Binary Code and Music Rolls

Joyce Brite's post on this subject reminds me of a device I saw
demonstrated on UK TV a few years back. It was an 1830s version of
(of all things) a fax machine!

It used a pair of identical pendulums: one to send, the other to
receive.  A synchronising pulse on the connecting wire released a
latch so both pendulums started swinging together.  The sending end
swept a wire over the message to be sent, written in conductive ink.
The receiving end swept a wire over treated paper.  Whenever the
message was detected, the current flowed and so made a mark in the
treated paper.  The pendulums' timing made the mark appear at the same
position on the swept line.

When each pendulum reached the end of its stroke, it was caught by the
latch, the paper a step moved by some mechanism and the cycle started
over again.  The latch kept both machines in synchronisation.

The TV programme (by Tim Hunkin, I recall) showed an old machine
and made a copy out of bits of wood.  It worked quite well, the sent
message being quite recognisable.

All this is clearly a development of the sort of machine devised by
Morse -- the Fax code is another form of digital signal, with con-
tinuously-variable times between on and off states (while Morse used
fixed times, the familiar 'dot' and 'dash').  It's fun to think that
the Fax predates the telephone by some decades!

Julian Dyer