TELEMETER (from Gk. ripte, te/c, afar + pirpov, metron, measure). An instrument for measuring the distance to a remote object, used in surveying and in military operations by engi neers and artillerists. In the Boulange telemeter, the distance from the observer to a cannon or ex ploding shell is ascertained by measuring the time consumed by the sound in reaching the ear. There are many forms of telemeter, which consist for the most part of telescopes and mirrors by means of which angles can be read and the dis tance computed. Gautier's telemeter is a type of this class of instruments, and depends upon the double reflection of a beam of light, as in the ease of the sextant, and the measurement of a short base line at the point of observation. The telem eter of the United States Coast and Geodetic Survey is more generally known among American engineers as the stadia (q.v.), and in Great Brit
ain as a tachometer. It consists of a mounted tele scope with two extra horizontal cross wires that intercept a certain number of divisions on the image of the graduated rod held upright at the distant point. The distance of the rod from the instrument is obtained by multiplying the read ing by a constant factor which depends upon the construction of the telescope. Stadia measure ments are particularly useful in making a rapid survey or reconnaissance and are accurate to about one part in 700. The name telemeter is also applied to an instrument which is connected electrically with indicating apparatus such as a meter or gauge and furnishes a similar record at a distant station. See RANGE-FINDER. Con sult Baker, Engineer's Surveying Instruments (New York, 1892).