Sources of Error indicated in the Great Trigonometrical Survey 179 The appliances and methods of the Great Trigonometrical Survey 186 By the transit of the Sun, or of a star By the method of equal altitudes Obtaining latitude by observation in the Prime Vertical Collimation. Level and Azimuth General Surveys. Field Records. I. TRAVERSING WITH THE CHAIN AND CROSS-STAFF facing page 94 II. CHAIN-SURVEY OF AN ESTATE (Record No. I.) III. CHAIN-SURVEY IN A Town (Record No. II.). IV. COMPASS-SURVEY (Record No. III.). V. THEODOLITE-TRIANGULATION-SURVEY VI. THEODOLite-traverse-SURVEY (Record No. IV.) ALL Geodetical operations may be said to be generally comprised under the three heads of Surveying, Levelling, and Setting out, or locating. Surveying generally consists in taking the measurements and observations on which a plan, chart, or map of the natural and artificial features of a tract of land or water may be based; although this does not strictly apply to some special branches, such as geological surveys; the term itself is also sometimes used to include levelling. General surveys may be classified in three ways: either according to the nature and scope of the ultimate object, or in accordance with the instruments used in the work, or the scale of the intended plan. Survey work of the highest and most perfect type is known as Great Trigonometrical Surveying, which B |