Railroad engineers' field-book and explorers' guide; Especially adapted to the use of railroad engineers on location and construction, and to the needs of the explorer in making exploratory surveys

by H.C. Godwin

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. 1890 ...first thing to do is to establish some point G in the alignment from which a good view--if possible--may be had of the mouths of any shafts which it may be required to sink, and also of two distant points A and B, also in the same straight line. If the instrument is then set up at Cand the telescope clamped on to A, on reversing it the point B should be intersected. By repeated trials the three points A, B, and C are then established in the same straight line, and these points should be permanently marked. In order to obtain the centre-line of the tunnel, say at the left end, another point G in the same line as AB must be given, and the centre-line is then obtained by the production of AG. But suppose the work is to be carried on also from one or more shafts as EF, then the alignment has to be "dropped" from ED to the elevation of the tunnel at F, and in this operation the greatest care is necessary. There are three or four ways in which this can be done, but the following is that usually adopted for tunnel-work, as it admits of greater accuracy than the others, which are more suitable for simpler mining Two instruments such as that shown in Fig. 58 should be firmly bolted on either side of the shaft as D and E, and near to its edge, both being lined in vertically over the centre-line of the tunnel. Each.instrument consists of a plate p--with a narrow vertical slit in it and scale s attached--which can be moved sideways by means of the screws a and b, so that it can be set to any desired reading on the scale--the scale being read by a vernier v attached to the main body of the instrument. Having set these two instruments approximately in line, then, by a series of observations taken at different times,--so as to counteract as much as p...

74 pages, Paperback

First published August 4, 2014