Pictures via a pendulum

The invention of the fax machine

Sending images through telephone lines to be reconstructed at the receiver’s end as a facsimile of the original — or fax — is nowadays being overtaken by other forms of electronic communication. But remotely printed paper messages still have many uses, and have done for more than 150 years. It might surprise you to know that the fax machine was invented decades before the telephone.

The Scottish shepherd

Sending a message by wire became possible with the start of telegraphy. But what about the amazing prospect of sending a signature or picture? In answer to the question in last month’s Pioneers’ Page, this technique was first demonstrated in the 1840s by a Scotsman, Alexander Bain.

Bain was born in 1811 in Caithness, in the far north of Scotland, one of 13 children of a crofter. As a boy, he helped to look after the sheep, but on leaving home he trained as a clockmaker, eventually moving to London in 1837 to pursue his trade. As well as mechanical devices, Bain was fascinated by electricity. In 1841, he patented the world’s first electric clock, which worked with a pendulum moved by electromagnetic impulses; this was to be an important step on the road towards the fax machine, which became Bain’s next invention.

A vital element of his "recording telegraph" was synchronization of the pendulums of two clocks which, for the scientist’s initial experiments, were about 70 kilometres apart in Edinburgh and Glasgow. Whenever the Edinburgh pendulum moved, a pulse of electricity went along a telegraph wire to a solenoid on the Glasgow pendulum that moved it simultaneously. Attached to each pendulum was a metal stylus. At Edinburgh, this swept backwards and forwards across a picture etched in copper (or, later, printer’s type), and when it met a line in the drawing an electrical contact was made. The signal made the Glasgow pendulum move across paper soaked in potassium iodide, which changes colour when an electrical current passes through it.

Scanning line-by-line

A crucial feature of the recording telegraph was its use of scanning. The copper picture that was being transmitted was moved along by tiny amounts with each sweep of the pendulum; at the receiving end, the sensitive paper was on a roll that advanced with each stroke. Thus, a facsimile image was gradually constructed, line by line.

Bain was granted a British patent on his device in 1843. His invention was later improved by another Briton, Frederick Bakewell, whose system used revolving drums covered with tin foil. The image was drawn onto the transmitting drum with a non-conductive material. The drum was then scanned, while at the receiving end, an image was produced on chemically treated paper wrapped around the second drum. Bakewell gave the first public demonstration of a fax transmission in 1851 at the Great Exhibition in London.

The Italian priest

Despite these successes, it remained a problem to achieve perfect synchronization of the transmitting and receiving ends of the first fax systems. The challenge was taken up by an Italian priest, Giovanni Caselli (1815–1891), who researched into the telegraphic transmission of images while teaching physics at the University of Florence. In 1860, working in Paris, he built a machine that he named a "pantelegraph". Essentially a giant, 2-metre-tall version of the earlier devices, it overcame the synchronization problem by triggering pendulum movements with extremely accurate clocks that operated independently of the electric current sent down the telegraph line.

The pantelegraph was widely acclaimed, and France’s Emperor Napoleon III gave it his backing. Caselli was allowed to use a telegraph line between Paris and Amiens to test the device, which he patented in 1861. A commercial fax service was started in 1863 between Paris and Marseille, followed in 1865 by one between Paris and Lyon. Thousands of faxes were now being sent across France by pantelegraph.

However, the pantelegraph failed to become a long-term success. It was not promoted well enough, and more simple forms of telegraphic transmission ultimately prevailed. It serves as an example of a technology that did not find a niche because it was ahead of its time. Nevertheless, four years before the birth in Scotland of Alexander Graham Bell who patented the telephone, Scotsman Alexander Bain had arrived at the concept of image scanning that was to be the basis of not only the fax technology of the future, but also of a fundamental technique of television.