GEODESY. A word occasionally used, which literally signifies the division of the earth, in which sense it is synonymous with land surveying ; but it is usually em ployed in a more general sense to denote that part of practical geometry which has for its object the determination of the magnitude and figure either of the whole earth, or of any given portion of its sur face. In this sense it comprehends all the geometrical or trigonometrical opera tions that are necessary for constructing a map of a country, measuring the lengths of degrees, Sm. In order to con struct an accurate map, or determine the form and dimensions of a country, it is necessary, in the first place, to determine the absolute distances between the seve ral stations or points ; secondly, to de termine the azimuths of the lines thus measured, that is, their situation with respect to the meridian ; and thirdly, the differences of latitude and longitude of the stations. The operations necessary
for determining the absolute distances, comprehending the measurement of a base, the observation of angles, the com putation of the sides of the triangles, and their reduction to the same level, are called the geodesical or geodetical opera tions; while those which are required for determining the azimuths and lati tudes are called the astronomical opera tions. The determination of the figure and dimensions of the earth is a problem of very great importance to astronomy and geography, and has accordingly at all tunes been subject of much interest to matheinaticilms ; but it is only since towards the middle of the last century that operations on an adequate scale for its solution have been undertaken in dif ferent parts of the world. Further de tails do not come within the scope of this volume. See THEODOLITE.