TELEGRAPH 615 gives a signal by breaks of the circuit, repeated a different number of times for different offices on the same wire. As this is heard by the operator at the receiving station, he sets his machine in motion, and the type wheel at its starting point, and signals back that he is ready. No further attention is required on his part, while the machine goes on, printing the communication in Roman capitals upon the long strip of paper regularly supplied to the type wheel. From 250 to 260 letters as a maxi- mum can be accurately printed every minute, and over 3,000 words an hour of press news, partly abbreviated, have been sent over the wires with a single instrument. The House printer was the parent of many others work- ing on the same principle, the " step by step " movement, in which each break or close of circuit allows a tooth of an escape wheel to pass; a type wheel being on the same shaft, a new letter appears for each tooth that es- capes. On May 20, 1856, Mr. Hughes patent- ed a telegraph, in which the feat of printing a letter with every impulse or wave of the electric current was accomplished. In the other telegraphs, as already described, sev- eral impulses produced by successive makes or breaks of the circuit are required to form a single letter; this in House's telegraph va- ries up to 14 breaks, the maximum required for repeating the same letter, and averages about 7 impulses; and in the Morse system the average is about 3-J impulses, those which make lines being of longer duration than those which make dots. The saving of time thus effected by the Hughes instrument is of great importance, especially on long lines in which an appreciable amount of time is expended in the passage of the current. In long lines of submarine telegraphs, as will b noticed be- low, a greatly increased resistance is experi- enced in charging the wires with the electric current, and the impulses necessarily succeed each other with extreme slowness and diminu- tion of force. The type wheel in the Hughes system is provided with 28 types ; it is kept in rapid revolution during the whole time of op- erating, and is so perfect in its movement that, though the revolutions may be from 100 to 140 a minute, the variations of two machines at different stations do not exceed ^ of a second in several hours. At- the instant one of the 28 keys is depressed, the current entering the magnet at the distant station causes the strip of paper to be brought against the type oppo- site to it at the time, and receive the impres- sion in ink while this is rapidly carried round with the wheel. The operator can send an average of two impulses with each revolution of the type wheel, thus making the capacity of the instrument 200 letters or 40 words a min- ute, and the maximum is much above this. The regulators or governors of the clockwork which carries the type wheels at the different stations are springs of the same musical tone, which consequently vibrate the same number of times a second, and which control by their vibrations the escapement of the apparatus. The power of the electric current required is reduced in a wonderful degree by the combi- nation of the natural magnet and the electro- magnet, making only so much electricity neces- sary as will neutralize the magnetism in the natural magnet by causing magnetism of an opposite polarity to be created in the poles of the electro-magnet. This extreme delicacy, however, renders the telegraph liable to be interrupted by atmospheric electricity, such as is developed previous to and during the con- tinuance of the aurora borealis. It is asserted that this instrument can work upon a longer line without the aid of repeaters than any oth- er, and this with an extraordinarily low battery power. In the winter of 1858 a new instru- ment was perfected by G. M. Phelps of Troy, combining the most valuable portions of both the House and Hughes patents, which has been introduced with great success on nearly all the lines formerly using those inventions. This has been termed the " combination " in- strument, and has the advantage of being able to work through a much longer circuit than the House machine, with a smaller battery, as well as of being much simpler. The keyboard and transmitting machinery of this instru- ment are precisely like those of Hughes, as is also the printing apparatus, with the excep- tion of the electro-magnet, which is of the or- dinary form, and operates upon the type wheel through the medium of compressed air as in the House machine. The vibrating spring used by Hughes as a governor is superseded in the combination instrument by a most ingenious electro-magnetic governor, the invention of Mr. Phelps. It consists of a hollow iron drum, geared to the transmitting cylinder and type wheel of the instrument and moving with them, but much faster. If the machinery has a ten- dency to revolve too rapidly, the increased cen- trifugal force, acting upon a detached section of the drum, actuates a series of levers inside, by which a spring is raised, closing the circuit of a local battery through an electro-magnet. A friction brake, which is applied to the re- volving drum by the attraction of this magnet, instantly reduces the speed to the required limits, when the local circuit is again broken. The combination instrument is considered the most perfect printing telegraph for long lines yet produced. The Anders printing telegraph, patented in 1871, and worked by magneto-elec- tricity, is designed for private lines, though capable of operating over distances of 45 m. Dial Telegraphs. In these instruments the step by step movement is generally employed, but the escape wheel does not carry a type wheel, nor do the printing accessories enter into their construction. A light needle is car- ried around with the escape wheel and points at the successive letters. They are thus vis- ual and not recording telegraphs. In England, the " Magnetic Telegraph Company " employed
