THE TELAUTOGRAPH
Before going any further we must have clear ideas on the subject of electrical resistance, upon which the whole system of the telautograph is built up. Electricity resembles water in its objection to flow through small passages. It is much harder to pump water through a half-inch pipe than through a one-inch pipe, and the longer the pipe is, whatever its bore, the more work is required. So then, two things affect resistance—size of pipe or wire, and length of pipe or wire.
The wires WW’ are very fine, and offer very high resistance to a current; so high that by the time the current from battery B has passed through all the wire loops only one-fifteenth or less of the original force is left to traverse the long-distance wire.
The rheostats act independently of one another. As the pencil moves over the transmitting paper, a succession of currents of varying intensity is sent off by each rheostat to the receiving station.
The receiver, to which we must now pay attention, has two arms DD’, and two rods FF’, corresponding in size with AA’ and CC’ of the transmitter. The arms DD’ are moved up and down by the coils TT’ which turn on centres in circular spaces at the bend of the magnets MM’. The position of these coils relatively to the magnets depend on the strength of the currents coming from the transmitting station. Each coil strains at a small spiral spring until it has reached the position in which its electric force is balanced by the retarding influence of the spring. One of the cleverest things in the telautograph is the adjustment of these coils so that they shall follow faithfully the motions of the rods LL’ in the transmitter.
By kind permission of The Telautograph Co.
An example of the work done by the Telautograph. The upper sketch shows a design drawn on the transmitter; the lower is the same design as reproduced by the receiving instrument, many miles distant.
We are now able to trace the actions of sending a message. The sender first presses the button E to call the attention of some one at the receiving station to the fact that a message is coming, either on the telephone or on the paper. It should be remarked, by-the-bye, that the same wires serve for both telephone and telautograph, the unhooking of the telephone throwing the telautograph out of connection for the time.
He then presses the lever S towards the left, bringing his transmitter into connection with the distant receiver, and also moving a fresh length of paper on to the platform P. With his pencil he writes his message, pressing firmly on the paper, so that the platform may bear down against an electric contact, X. As the pencil moves about the paper the arms CC’ are constantly changing their angles, and the brushes ZZ’ are passing along the segments of the rheostats.