Tekrit (anc. Birtha). A town situated on the Euphrates, in Mesopotamia. It was unsuccessfully besieged by Sapor I., king of Persia, in 260.
Telegraph, Field or Flying. During the civil war (1861-65) in the United States a signal corps was organized, whose duties extended to the management of field telegraphs, and light lines, when the formation of the country was such that aerial signals could not be used, or it was for any reason desirable that short electric lines be extended. It has been demonstrated that electric instruments may be of the most simple construction; and electric lines can be set up, and be utilized in places where a few years ago it was deemed impracticable to employ them; and can be worked without other skilled labor than that of the soldiers attached to the posts, and with no apparatus but such as can be had at a trivial expense. There is no reason why, with properly drilled parties, electric lines may not be thrown out in the moments which precede, or even during the progress of, a battle, and be so worked as to lessen infinitely that difficulty of rapid communication which has so often caused disaster. With a corps well organized and well equipped, the connection between the corps of an army, and between the corps headquarters and general headquarters, ought to be perfected in a very few hours after the halt of the army. The field lines of the Signal Corps consist of rolls of wire carried in light-wheeled vehicles, and light “lance poles,” us they are called, on which the wire is stretched when necessary. The wire made for the purpose is of small strands of iron and copper twisted, to give it strength and flexibility. It is insulated with prepared india-rubber, or other material, and wound on reels which, in an emergency, can be carried anywhere by hand, while the wire reeling out can be raised upon fences, fastened to trees, or laid along the ground. The instruments used at first were of a kind known as the Beardslee instrument. These instruments are worked without batteries, the electric current being generated by revolving magnets. They were “indicating,” an index upon a dial pointing, at the receiving station, to whatever letter was designated by the index handle upon a similar dial at the sending station. There were as advantages attaching to this instrument, that it was portable and compact, could be set at work anywhere, required no batteries, acids, or fluids; and what was thought of importance in the early days of the civil war, and while the corps was a temporary organization, it could be worked by soldiers without skill as operators. The defects were, that messages could not be sent as rapidly or as far as by some other instruments. Nor could several instruments work easily upon a single circuit. For some uses on the field of battle, or under fire, where the attention of the reader is disturbed, it is, perhaps, as good an instrument as has been devised. With a permanent corps, or at secure stations, it gives place to some of the forms of signal or of sound instruments. The instruments upon field lines may be of very simple structure. The signal instruments, either the needle or the letter instruments, can be used in actual conflict, if the reports of heavy guns or other disturbances of action render reading by sound unreliable. The manufacture of both instruments and batteries has been improved, until there is now no trouble in carrying either in the field in the roughest campaigns. The difficulty in reading from telegraphic instruments by sound, which has been the greatest obstacle to their use, can be almost done away with by using them with codes of easy signals. In the Prussian army, also, the electric telegraph is applied for field purposes. Morse’s system is used. Each headquarters of an army and each army corps, has a telegraphic division of 3 officers, 137 men, 73 horses, and 10 wagons. Two of the latter are fitted up as operating-rooms, and the other 8 are used for carrying poles and other material, including 5 miles of wire to each wagon, which can be reeled off by the moving of the vehicle. Of the whole 40 miles, 5 are insulated, and can be run along the ground. It will be seen that each army corps can put out 40 miles of line without recourse to other wires, but use is always made of lines found in the country, in case they will answer. Single poles of light material are used, without joints, and about 10 feet long, and only every third pole is put in the ground. The [personnel] is brought into the army from the civil telegraphic service at home. While in the field, the operators assume military rank, and, like agents of the Post-office Department, are known as “military officials,” not as “military officers.” The men are on a footing with train-soldiers. The operating-wagons are a little larger than the Rucker ambulances of the U. S. service, but much heavier. Just in the rear of the driver is a partition shutting off the rear portion of the carriage. At his back, and under his seat, is a capacious box, in which are carried tools, and the material necessary in telegraphing. On one side of the rear closed portion is a neat table with a compact operating instrument on it, and a battery under it; and on the opposite side is the operator’s bench, the space underneath it being also economized. On the outside near the table are sockets, with thumb-screws connected with the battery, to receive the wires. During the Franco-Prussian war, besides keeping the king in telegraphic communication with his ministers, lines were run from Gen. von Moltke’s headquarters to all the different corps in the field. The telegraph corps always evinced admirable promptness in keeping the lines closed up as the army moved forward. In Great Britain, the system of military telegraphy forms part of the duties of the Royal Engineers.
Telemeter. An instrument for determining long distances. (See [Range-finder].) One of the best-known telemeters is the invention of Capt. A. Gautier of the French army. It consists of a short tube containing two mirrors set at an angle of 45° with each other, one of which is fixed; the other admits of a slight rotation. A hole in the side of the tube allows the image of a secondary distant object on the prolongation of the base-line to be brought in line with that of the distant object whose distance is to be measured. An observation is next taken from the other end of the short base-line, and the image of the secondary object again brought in contact with that of the principal object by rotating a ring on the front of the tube. The extent of this rotation (as denoted by a scale), gives a factor which, multiplied by the base-line, gives the required distance.
The Boulongè telemeter is an instrument devised for ascertaining the distance to a point by means of sound proceeding from the point to the place of observation. The one used for artillery consists of a glass tube about 6 inches in length, filled with a transparent liquid that does not freeze except with intense cold. In the liquid is a metallic disk, which moves freely from one end of the tube to the other. It is so adjusted that the motion will be uniform and comparatively slow. The tube is inclosed in a brass case, to which is attached a scale, after the fashion of a thermometer. This scale is marked for each hundred yards up to 4000. The divisions on the scale show the distance, in yards, through which sound will travel in air during the time required for the disk to descend over the space on the scale marked by the corresponding number of yards. The instrument must be held vertically, or as nearly so as possible. To arrest the motion of the disk at any point, the instrument is quickly turned to a horizontal position.
To use it for determining the time of flight of shells it is held in the right hand, back of the hand up, with the zero of the instrument to the left; a turn of the wrist to the right brings the instrument vertical, with the zero end uppermost; the disk then descends, and a turn of the wrist to the left arrests its motion. The observer, holding the instrument as described, watches for the flash of the shell, and upon seeing it instantly brings the instrument to a vertical position; upon hearing the report from the shell he instantly turns it back again. The position of the disk indicates the number of yards from the observer to where the shell exploded.
To ascertain the distance to an enemy’s battery, the instrument is held and turned in the same manner. The observer watches for the flash of a gun; observing which, he turns the instrument, and when he hears the report turns it back and reads off the distance. Each hundred yards on the scale is subdivided into quarters.
The telemeter invented by Capt. A. Gautier of the French army is an instrument for measuring, with a great degree of approximation, any difference, not exceeding three degrees, which may be exhibited in the bearing of a distant object by viewing it from different points of a base-line transverse to its general direction from the observer. The instrument, in its simplicity, accuracy, and portability, recommends itself in all cases where a knowledge of distances is desired at any moment and with the least possible delay; such, for instance, as range-finding, river-crossing, reconnoitring, and the like. A slight acquaintance with its use on such occasions enables the observer to estimate, with more than ordinary promptitude and precision, the distance which it might be all-important to obtain.
The instrument resembles in shape and size one barrel of an ordinary reconnoitring- or field-glass. The case in which it is carried is fashioned so as to answer as a handle for holding the instrument when making observations. Within the barrel of the instrument are placed two mirrors at an angle of 45° with each other; this angle can be varied within certain limits by means of a milled-headed screw acting on one of them. The mirrors are thus made to operate upon the principle of the sextant. A slot on one side of the barrel permits the rays of light from an object to fall upon one of the mirrors, from whence they are reflected upon the other mirror, and the image is seen through the eye-glass at the small end of the instrument. At the front or large end is fixed, in a ring surrounding the barrel, a prism, whose displacement modifies the direction of an object seen through it. At the rear of the instrument is a small eye-glass, by means of which the observer sees, over the mirrors and through the prism, the object which is before him, and by double reflection in the mirrors the object to the side of him.
The American general Berdan has invented a large telemeter for garrison and sea-coast service which has been tested in Germany in 1875 and 1876 and found to be very exact in the determination of distances. He has also constructed a new model for field and mountain artillery which can be packed up and transported on horseback.
Telephone. An instrument for reproducing sounds, especially articulate speech, at a distance, by the aid of electricity or electro-magnetism. It consists essentially of a device by which currents of electricity, produced by the sounds, and exactly corresponding in duration and intensity to the vibrations of the air which attend them, are transmitted to a distant station, and there, acting on suitable mechanism, reproduce similar sounds by repeating the vibrations. Telephones were recently used by Sir Garnet Wolseley in the war in Zululand, and are being rapidly adopted in European armies.