Page:The American Cyclopædia (1879) Volume XV.djvu/642

614 TELEGRAPH paper and blackens it by decomposing the chemical. The current was formerly sent over the line by the key, as in the Morse system ; but to call attention a bell was used, and this usually required the local circuit. Mr. Bain had at this time fully developed a plan for transmitting signals with a rapidity far greater than could be effected with the key, and this plan is the same as that now used in the revived system. In place of the key a fillet of paper was punched with lines and dots representing a message. This was passed over a metallic roller with great speed, and a fine wire which rested on the paper entered each hole as it moved and completed the circuit through the roller. The receiving machine was made to run at a speed corresponding with that of the transmitting machine, and the perforated dots and dashes were reproduced in blackened dots and dashes. The advantage of this system lies in the transmission of long messages, which are received and prepared by several opera- tors, at great speed. Until recently this speed could be obtained only on short circuits, the marks on long circuits running into each other and becoming illegible. Later improvements have enabled messages to be sent from Brussels to Ostend and back at the rate of 450 words a minute; and the American instruments have sent between Washington and New York 5,250 letters a minute, requiring 10 perforators to feed it, 10 copyists, and two operators. Fac- simile Telegraphs. Electric copying or facsimile telegraphs are modifications of the automatic chemical. They originated with F. C. Bake well of England in 1850, and have been improved by Caselli, Bonelli, and others. In them the mes- sage is written with a pen dipped in varnish upon a sheet of tin foil, which is then laid around a metallic cylinder, corresponding pre- cisely in its size, rate of revolution, and longi- tudinal movement, with another cylinder at the receiving station, which is covered with chemically prepared paper and provided with a pointer like that of the Bain chemical tele- graph. These cylinders being set in motion at the same instant, the point of the registering apparatus makes a continuous colored line, running round the cylinder in a close spiral so long as the metal style at the other station presses upon the tin foil ; but as this passes over the lines of varnish a break in the circuit occurs, causing an interruption of the colored line at the other station. The blank spaces thus pro- duced will be found when the lines have been drawn over the whole paper to be a facsimile of those written in varnish upon the tin foil. The lines, though drawn as spirals upon the cylinder, appear as parallels when the paper is taken off. About 10 revolutions of the cylin- der, making as many parallel lines, are sufficient to complete one line of writing ; a cylinder 6 in. in diameter affords sufficient length for about 100 letters of the alphabet in one line ; and as the rate of revolution is not less than 30 in a minute, 300 letters or more may be transmitted in this period. A message in ci- pher can be sent by this method without risk of error, and even invisible messages written in colorless varnish may be received and im- pressed in invisible characters upon prepared paper, to be afterward brought out by chemi- cal means; thus, if the paper be moistened with diluted acid alone, no visible mark is left upon it until it is brushed over with a solution of prussiate of potash, when the lines appear in their blue color. Great improvements in the autographic telegraph have been made by Ca- selli, who has succeeded in making dark letters upon a white ground. His instruments have been used on some of the French lines since 1862. Printing Telegraphs. Royal E. House, of Vermont, received a patent in 1848 for an admirable long-line printing apparatus, which was first used in 1847, sending messages in Roman capitals between Cincinnati and Jef- fersonville, Ind., 150 m. The necessity of avoiding the peculiar features upon which other telegraphic systems were established, in order to give to it a distinctive and pat- entable character, added greatly to the diffi- culties of the undertaking, which after nearly six years of labor were overcome by the in- genuity and perseverance of Mr. House. The apparatus is very complicated, and little more can be attempted than to state its great pow- ers of execution and its perfect accuracy. The mechanical movements of this machine are set in action by hand labor applied to a crank, which works an air pump for supplying a cur- rent of condensed air, which under the control of the electric current carries forward the move- ments of the composing and printing apparatus, so that each letter may be printed at the exact instant that it is struck upon the keyboard of the instrument. This keyboard, which resem- bles that of a piano, is connected with the elec- tric current, and as the keys are struck the circuit is opened and closed with the move- ments of a circuit wheel which controls the movements of the type wheel. A complete revolution of the circuit wheel, coming round again to the same letter, breaks and closes the circuit 28 times, and other letters a less number according to their arrangement on the type wheel. The printing apparatus is quite distinct from the circuit, but the composing apparatus forms a part of it. The impression of the let- ter is produced by a blackened ribbon being pressed against the paper by the type. From the voltaic battery of one station, the current passes along the wire to the next station, then through the coil of an axial magnet to the in- sulated iron frame of the composing machine, and thence to a circuit wheel revolving in this frame. Through a spring that rubs on the edge of this wheel it passes into the return wire, and through another battery back to the first station to pursue the same course through the composing machine and magnet there, and all others upon the line. In sending a message, the operator sets his machine in motion and