the end of the line into connection with each sending instrument in turn, so as to allow each clerk to send a letter turn-about. Thus, if there are five clerks there will be five messages going over the wire together, one letter at a time. This is done by causing the end of the wire to sweep round a metal circle divided into five segments, each segment communicating with the sending apparatus of a clerk. At the receiving end the line also sweeps over a similar circle of five parts, each part being in communication with a receiver. Now, as the revolution of the receiving end of the line is made to keep perfect time with the revolution of the sending end, the individual letters of the message, though apparently all jumbled together, are distributed to their proper receivers, and five separate messages are the result. Meyer's system was originally worked with Morse receivers; but lately it has been applied by M. Baudot to the Hughes type-printing instrument. This beautiful apparatus, which is the invention of Professor D. E. Hughes, better known as the discoverer of the microphone, actually prints the message in Roman characters, and is extensively used on the Continent. The principle of synchronous action between the sending and receiving instruments is also involved in it, the types of the receiver being set round a small wheel which turns at a uniform rate, and the sender, knowing the position of the receiving type, sends a current which presses the paper against the wheel and prints the letter he intends. Baudot's union of the Meyer and Hughes systems gained for him the high distinction of a Grand Diploma of Honour at the Paris Electrical Exhibition.

Another very useful little type-printer is the

E

Exchange instrument, now employed in large cities for telegraphing the latest prices of stock to private subscribers. Like the Hughes instrument, it has a type-wheel working in synchronism with the sending instrument, and the message is printed on a travelling ribbon of paper. A number of these, each in a separate house, can be connected in the same circuit. and operated together by the same current.

In the Exchange or Stock telegraph instrument a small type-wheel is inked by a cylindrical pad; and the paper, which is coiled in a boat-shaped pannier, is moved forward betwixt the printing of every two letters by a stream of intermittent currents actuating an electro-magnet placed in the base of the apparatus ; and the printing of a letter is performed by stopping this current so as to stop the paper and then by means of a signal current through a separate electro-magnet, pressing the paper up against the type-wheel while the particular letter is just over it. Besides the Exchange instrument there are a number of local telegraphs, such as the A B C instruments of Sir C. Wheatstone, for private correspondence, and in America the domestic telegraph and call system, by which a householder can summon a cab, a doctor, a policeman or other assistance, through the medium of a central station or exchange; these local telegraphs are, however, being superseded by the telephone. There are also several copying telegraphs whereby a copy of an autograph writing or a pen and ink sketch may be reproduced at the remote end of the telegraph line. Bakewell, Caselli, D'Arlincourt and others have devised ingenious apparatus for this purpose, but as they are not in actual use we need not linger over them. They require synchronous

Cowper's

motion at the two ends of the line; and Bakewell's copy is produced by the current decomposing a chemical solution in the receiving paper and thus marking it. In Mr. Cowper's writing telegraph, no such motion is required, and a copy is made of any handwriting while it is being written. It is much simpler and more direct in its action than the roundabout systems just mentioned. Telegraphic Pen, as we may call it, since it operates like a pen so many miles in length, is probably the first literal "telegraph " or "far-writer," and as the telephone permits any person to converse by wire, so this supplementary invention enables any one to write by wire. In designing his pen Mr. Cowper was guided by the principle that all points in a curve can be determined by the perpendicular length of two lines drawn from fixed co-ordinates at right angles to each other, just as the track of a ship is laid down on a chart by its latitudes and longitudes. Every point in a line of writing therefore can be determined by its distance from such fixed lines, every stroke of the writing pencil or pen can be resolved into horizontal and vertical components; it follows that if these components could be transmitted by wire continuously as the writing is being done, and recombined at the receiving end on a pen or pencil there, the latter would reproduce the original writing. It is this feat which Mr. Cowper has accomplished.

He employs for the purpose two separate circuits, one to transmit the up and down range of the pen, and the other the sidelong range. Each circuit consists of a battery, a set of variable resistances and the line, and for the sake of explanation it will be sufficient to consider any one of these, say that which transmits

the up and down range of the sending style. Fig. 24 represents in theory the connections for sending a written message, P is the pencil which the writer takes in his hand and writes with in the ordinary manner; the paper being pulled by clockwork slowly under the point. A metal arm a, fitted at its point with a contact piece, is attached to P, and the working pole of the battery is connected to a. Between the arm a

and the line, there is inserted a series of resistance coils R, whose contacts or poles are thin metal plates, placed edgewise, and insulated from each other by sheets of paraffined paper. There are thirty-two of these coils and plates. Now the arm a is so connected to the pencil p that as the latter writes the arm moves lengthwise, that is, in the direction of its axis, across the edges of the resistances R to an extent equal (or it may be proportional) to the vertical range of the

pencil. By pushing across these resistances in this manner it puts in or takes out of circuit a number of the resistances proportional to the extent of its movement. Hence the strength of the current in circuit is varied according to the vertical range of the pen. Similarly in the other circuit provided for the transmission of the side-long motion, the arm a1 glides over the resistances R1, and puts in or takes out resistances which vary the strength of the current according to the direct side-long motion of the pencil. It will be understood that the actual movement of the pen is very slight, being comprised within the dimensions of any single letter formed, for the movement of the paper itself obviates the necessity of the pen shifting from letter to letter.

The receiving apparatus is sketched in Fig. 25. It