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 Surve}' 

 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) b}' 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 3'ear 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 

 metiiods 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 arc 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. 



