572.—The General System of Working the Tacheometer, with sufficient detail for practice, would take too much of our limited space to be given here. We now have several good works published in Great Britain, in addition to the able paper by Mr. Brough before mentioned, such as The Tacheometer: Its Theory and Practice, by Mr. Neil Kennedy; Surveying, by Whitelaw; Aid to Survey Practice, by L. D'A. Jackson, &c. There is a small work published in New York giving some details.[31] There are complete works in French, Italian, German, and Spanish. In French, Leves de Plans a la Stadia, by M. J. Moinot, engineer to the Paris, Lyons, and Mediterranean Railway, gives very complete instructions for all conditions of country, upon surveys which he has personally carried into practice with this instrument.
There are several tacheometers made upon the Continent, of more complicated forms than those herein described, but they do not produce better work.
573.—Field-books for the tacheometer are ruled in various ways in columns, which vary in number in different books from twelve to twenty. The French generally have fourteen columns, giving the number of the station, time, heights of line of collimation above point levelled, numbers of points selected, horizontal and vertical angles observed, reading of subtense webs and their differences, height of staff by reading central web, and columns for calculations and remarks; most English forms are more simple.
Fig. 249a.
Larger image
574.—A convenient protractor in which the equivalent of surface reading is taken from a scale upon its lower part directed from the centre of the protractor is here shown.
Fig. 250.—Perspective view of 5-inch omnimeter.