stadia (stadia)

[ stage, station, stadium: see stadium.] 1. A station temporarily occupied in surveying. 2. An instrument for measuring distances by means of the angle subtended by an object of known dimensions. The instrument commonly so called, intended for rough military work in action, consists of a small gla plate with figures of horsemen and foot-soldiers as they appear at marked distances, or with two lines nearly horizontal but converging, cro ed by vertical lines marked with the distances at which a man appears of the height between the first lines. 3. In civil and topographical eng in., the method or the instruments by which what are called stadia measurements are made. This use is almost exclusively limited to the United States, where this method of measuring distances is extensively employed. Stadia measurements are based on the geometrical principle that the lengths of parallel lines subtending an angle are proportioned to their distances from the apex of that angle, The e ential appliances for this kind of work are a pair of fine horizontal wires (which are usually of platinum, but which may be spider-webs, or even lines ruled or photographed on the gla ), in addition to the ordinary hori zontal and vertical wires in the diaphragm of a telescope, and a staff or graduated rod (the stadia rod) - these giving the means of measuring with considerable precision the angle subtended by the whole or any part of a vertical staff, and thus furnishing the data for determining the distance of the rod from the point of sight. This may be accomplished by making the subtending angle variable (that is, by making the wires movable) and the space on the staff fixed in length, or by having the angle constant (that is, the wires fixed in position) and reading off a varying length on the staff; the latter is the method now most generally used. The wires may be applied to the telescope of any suitable instrument, as a theodolite or transit-theodolite; but the method is specially well adapted for use in plane-tabling, the wires being inserted in the telescope of the alidade. This arrangement has been extensively used in the United States, and has given excellent results. The intervals between the wires are frequently arranged so that at a distance of 100 feet a space of one foot shall be intercepted on the rod; but there are also instruments made in which the number of wires is increased, the method of reading varying accordingly. stadiet, n. [ME., Yif a man renneth in the stadie or in the for longe for the corone, than lieth the mede in the corone for whiche he renneth. Chaucer, Boëthius, iv. prose 3. stadiometer (stā-di-om'e-ter), n. [ stadium ) + μέτρον , measure.) A modified theodolite in which the directions are not read off, but marked upon a small sheet, which is changed at each station. The distances as read on the telemeter can also be laid down. The stadiometer differs from the plane-table in that the alidade cannot be moved relatively to the sheet. 5886