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TELEGRAPH.  at an expense of £6,750,000. In 1869 there were about 7,000,000 messages sent, a number which increased to 22,459,775 in 1879, and 90,413,123 in 1900. In this last year the receipts from telegraphs were £3,460,492 and expenditures £3,748,930, leaving a deficit of £288,438. This deficit is due largely to the reduced rate at which newspaper messages are transmitted, there being an actual loss of over £250,000 on this class of business. With governmental ownership have come improved service and reduced rates. Where in 1870 it cost from 3 to 6 shillings to send a message from London to Dublin, now a message of 12 words can be sent anywhere in the United Kingdom for 6 pence. In 1867 the average charge for a message was a little over 50 cents; now it is slightly more than 15 cents. In 1900 the Post-office Department controlled 11,188 telegraph offices, including 2337 railway offices, while the mileage of line is stated at 44,970, with 329,660 miles of wire.

Houston and Kenelly, Electric Telegraphy (New York, 1896); Loring, A Hand Book of the Electro-Magnetic Telegraph (New York, 1900); Maver, American Telegraphy: Systems, Apparatus, Operation (2d ed., New York, 1899); id., Quadruplex, with Chapters on the Dynamo Electric Machine in Relation to the Quadruplex (New York, 1893); Pope, Modern Practice of the Electric Telegraph (16th ed., New York, 1899); Prescott, Electricity and the Electric Telegraph (New York, 1892); Culley, Handbook of Practical Telegraphy (8th ed., London, 1885); Preece and Sivewright, Text Book of Telegraphy (9th ed., London, 1891); Bright, Submarine Telegraphy (London, 1898); Reid, History of the American Telegraph (New York, 1882). See also ;  TELEGRAPHERS' CRAMP. See .  TELEGRAPHY, In submarine telegraphy there are many variations from the practice on land lines. (See .) This is the case because the length of the line between stations is usually great and certain conditions attend the construction and laying of the cable bearing the conductor. The problem then involves the transmission of current along a conductor of great length and necessarily small cross-section with of course considerable resistance. In a long cable we have to consider the effect of the electrostatic inductive capacity as well as its conductivity. The cable acts as a (q.v. ), the core or conductor forming one of the plates or conducting surfaces, while the metallic sheathing acts as the other. As it takes a perceptible time for the cable to be charged and discharged when a current is sent through it, there is a certain limit to the speed of transmission of signals without their becoming confused and unintelligible. As the length of the cable increases, so does the time required for charging, and it was demonstrated by Lord Kelvin (1853) that the rate of signaling would vary inversely as the square of the length of the cable. So small is the current passing over the cable that it is impossible to use ordinary telegraph instruments on lines greater than 500 miles in
 * and.

length, and only up to 150 miles can an ordinary rate of signaling be maintained. It is necessary, therefore, to use some sensitive device such as a mirror galvanometer or a Thomson siphon recorder to receive the transmitted signals. The (q.v.) or some modified or special form of this instrument when used in cable telegraphy is of high resistance and considerable sensitiveness. The ordinary mirror receiver resembles the Thomson reflecting galvanometer, and has one coil and a suspended mirror to which the magnets are attached. The action is precisely the same as in the galvanometer, the amount and direction of the deflection depending on the intensity and direction of the current. A galvanometer with a suspended coil may also be used, or, what is more usual, some form of siphon recording receiver. The siphon recorder was invented by Lord Kelvin in 1867 and has since been greatly modified and improved by various cable engineers. It consists essentially of a coil of light wire suspended between the poles of a powerful magnet, capable of being deflected from its position of rest upon the passage of a current. As the coil moves its motion is transmitted to a siphon formed by a fine glass tube, one end of which dips into a vessel containing ink, while the other is near or in contact with a strip of paper which is moved through the apparatus by a motor, either electrical or clockwork. This glass pen will trace on the tape a line where the movements of the coil are indicated by curves or waves marked on the paper. These curves are above or below the line of rest, depending upon the direction of the current which passes through the coils. Thus to produce a dot a positive current is sent over the wire and an upward curve is produced on the record. Reversing the current gives a dash, and employing the Continental Morse alphabet described under, the various signals can be transmitted. With such recorders are employed either simple keys or automatic transmitters. The simple key consists of a pole-changing device by which a current in either direction can be sent over the circuit by simply pressing one of two keys. In automatic transmission, which is used on the transatlantic cables and other busy lines, the operator first punches in a paper strip holes corresponding to the proper signals, and then contact is made through the agency of rods or brushes as the tape is passed through the transmitter. These devices, however, can only be used on cables having heavy cores, but by their use a rate of 50 words or more a minute may be obtained.



In working cables it was soon found that their efficiency was increased and the effect of earth currents eliminated by inserting a (q.v.) between the transmitting instrument and