A treatise on land-surveying; comprising the theory developed from five elementary principles, and the practice with the chain alone, the compass, the transit, the theodolite, the plane table, &c

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1856 Excerpt: ... persons require the eye-piece to be pushed farther in than persons of ordinary sight, and old or longsighted persons to have it drawn further out. (.333) Supports. The Telescope of the Transit is supported by a hollow axis at right angles to it, which itself rests at each end, on two upright pieces, or standards, spreading at their bases so as to increase their stability. In the Theodolite, the telescope rests at each end in forked supports, called s, from their shape. These s are themselves supported by a cross-bar, which is carried by an axis at right angles to it and to the telescope. This axis rests on standards similar to those of the Transit. The Telescope of the Theodolite can be taken out of the Ys, and turned "end for end." This is not usual in the Transit. Either of the above arrangements enables the Telescope to be raised or depressed so as to suit the height of the object to which it is directed. A telescope so disposed is called a " plunging telescope." In some instruments there is an arrangement for raising or lowering one end of the axis. This is sometimes required for reasons to be given in connection with " Adjustments." (334) The Indexes. The supports, or standards, of the telescope just described are attached to the upper, or index-carrying circle. This, as has been stated, can turn freely on the lower or graduated circle, by means of its conical axis moving in the hollow conical axis of the latter circle. This upper circle carries the index, V, In mime instruments this circle is the under one. In our figures it is the upper one, and we will therefore alwnys speak of it as such. which is an arrow-head or other mark on its edge, or the zero-point of a Vernier scale. There are usually two of these, situated ex...