fax

How facsimile messages are transmitted from one remote fax machine to another, with the aid of communications satellite technology.

Transmission of images over a telecommunications link, usually the telephone network. When placed on a fax machine, the original image is scanned by a transmitting device and converted into coded signals, which travel via the telephone lines to the receiving fax machine, where an image is created that is a copy of the original. Photographs as well as printed text and drawings can be sent.

Alexander Bain, a Scottish mechanic, invented facsimile transmission over wires in 1843. His fax machine transmitter scanned a flat metal surface using a stylus mounted on a pendulum. Images on the surface of the metal were picked up by the stylus and could be transmitted via telegraph to a similar machine at the other end of the wire. The technique was limited in that documents to be sent had first to be transcribed onto a metal plate.

The world's first practical fax machine, the pantélégraphe, was invented by Italian physicist Giovanni Caselli in 1866, over a century before the first electronic model came on the market. Standing over 2 m/6.5 ft high, it transmitted by telegraph nearly five thousand handwritten documents and drawings between Paris and Lyon in its first year.

Various inventors improved upon the fax design until in 1924, the American Telephone & Telegraph Company (AT&T) developed their telephotography machine that was able to transmit photographs along long-distance telephone cables. On 4 March 1955, the first radio facsimile transmission was sent across the breadth of the USA.

The fax machine has continually been upgraded and is still in widespread use, either as a stand-alone machine, as a combination phone/fax system, or as an integral part of a PC system.