Electro-chemical copying of Caselli

In 1865 Italian physics professor Giovanni Caselli established the first commercial fax system, which linked Paris and several other French cities, using a device called a Pantèlègraphe which was a modification of Alexander Bain's original idea. He transmited nearly 5,000 faxes in the first year.Made of cast iron and standing more than 2m high, this primitive but effective machine worked as follows. The sender wrote a message on a sheet of tin in non-conducting ink.The sheet was then fixed to a curved metal plate and scanned by a needle, three lines to the millimetre. The signals were carried by telegraph to the marked out the message in Prussian blue ink, the colour produced by a chemical reaction, as the paper was soaked in potassium ferro-cyanide. To ensure that both needles scanned at exactly the same rate, two extremely accurate clocks were used to trigger a pendulum which, in turn, was linked to gears and pulleys that controlled the needles.