National Geographic : 1897 Oct
GEOGRAPHIC WORK OF THE U. S. COAST SURVEY 297 ington, and thereafter the precise determination of longitudes had merely to await the extension of the telegraph system from point to point within our own borders and throughout the world. As soon as the Atlantic cable had been laid in 1866, the Survey successfully undertook to determine our longitude from Green wich by the telegraphic method. Up to that time the longitude adopted for Cambridge, Massachusetts, in 1851, was used. The adopted value (4 h. 44 m. 39.5 s.) had been derived from many years of laborious observations of moon culminations, eclipses, occultations, and chronometer determinations, but this value was increased (in 1869) by 1.35 s., as the result of comparatively brief cable determinations. Similarly, the longitude adopted for San Francisco in 1855, as the result of 206 moon culminations, was increased in 1869 by 3.1 s., in linear measure about i of a mile, by the telegraphic determination. Within the past year the Survey has completed and adjusted its primary longitude net covering the whole United States and fixing for all time the astronomical longitudes of the points in cluded in it, not only in their relation to each other, but, in all probability, their final relation to the initial meridian of Green wich, since in this adjustment three transatlantic determinations by the Coast Survey and one by the Canadians have been used. Less need be said of the many latitude determinations, since the methods adopted, though admirable in their precision, involved no such radical improvement as that which the telegraph brought about in the determination of longitudes. On the other hand, however, the zenith telescope, as developed by the Survey, has in the hands of its observers contributed materially to our knowl edge of the variation of latitude. Reference has been made to the geodetic function of the Sur vey. It has measured an oblique arc, the last triangles in which have but just now been observed, extending from the northeast ern boundary to the Gulf of Mexico. To join this with the pri mary chain, as yet incomplete, of triangles along the Pacific coast, a great arc has been measured along the 39th parallel of latitude, the completion of which has been but recently an nounced. The adjustment of the triangulation along this great are and the adoption of a homogeneous system of geographic coordi nates will furnish the fundamental data for the coordination of all Government or State surveys for all time to come, if it be permitted to fallible human wisdom to make such an assertion.