SCIENCE 



[N. S. Vol. XLIV. No. 1123 



rect elevation of points far from their 

 coast. It is a work which demands the 

 highest degree of accurate observing and 

 painstaking endeavor. It calls for espe- 

 cially designed instruments and methods of 

 observation. These accurate elevations are 

 needed for the reduction of base lines to 

 mean sea-level, for engineering operations 

 of wide extent, and for the solution of 

 scientific problems concerning gravity, the 

 tides and other work. 



In this leveling of precision, the Coast 

 and Geodetic Survey has added much to 

 the world's work by attainments in field 

 operations, methods of reduction and scien- 

 tific study of errors involved. In its great 

 precise level net (greater than that of any 

 other nation) there are more than 15,000 

 bench marks, of which the elevations have 

 all been accurately fixed through a single 

 least square adjustment of more than 80 

 circuits with a total length of more than 

 25,000 miles. 



THE COAST SURVEY LEVEL 



Among the instruments of precision em- 

 ployed by the nations for precise level 

 work, it may be truly said that none holds a 

 higher rank than the type which has been 

 in use in the Coast and Geodetic Survey 

 since 1900. This level was designed and 

 built within the Survey, and after more 

 than fifteen years of constant service, in 

 all parts of the United States, has shown 

 itself to be indeed a superior instrument 

 for accurate and rapid leveling. 



Before the introduction of this level, the 

 average rate of progress was less than 60 

 miles a month. Recent work, which is of 

 much higher grade of accuracy, shows an 

 average of nearly 80 miles; and one ob- 

 server with a party of six men, last season 

 completed 120 miles of progress, or more 

 than 250 miles of single line in one month, 

 which constitutes a world record. 



Although precise leveling has been 

 brought to the highest perfection in Prance, 

 the Coast and Geodetic Survey, by the very 

 magnitude of its operations, by the instru- 

 ments employed, and by the economy in 

 speed and cost, is certainly without an 

 equal in the geodetic world. 



ASTRONOMIC DETERMINATIONS 



Considering astronomy as a definite part 

 of its geodetic function, the Survey has 

 added to the work done by the various na- 

 tions many hundreds of astronomic lati- 

 tude, longitude and azimuth determina- 

 tions, mostly at stations connected directly 

 with the great triangulation system. While 

 no great changes have been introduced in 

 latitude and azimuth work as far as instru- 

 ments are concerned, there has been a de- 

 cided change in speed and economy. 

 Methods of observing and of computing 

 have been standardized and this has greatly 

 aided the work. 



Since about 1904 all of the primary azi- 

 muths, in so far as was practicable, have 

 been observed by the triangulation party 

 during the progress of the work. It is be- 

 lieved that this plan gives the highest de- 

 gree of accuracy, for the measurements are 

 made under exactly the same conditions as 

 the triangulation with which they are con- 

 cerned, and the cost is very materially 

 reduced. 



TELEGRAPHIC LONGITUDES 



The formation of the great telegraphic 

 longitude net of the Coast and Geodetic 

 Survey is a geodetic feat worthy of special 

 note. No less than four transatlantic deter- 

 minations have been made which serve to 

 connect the longitudes of the United States 

 with Greenwich and Paris, and more than 

 50 stations are included in the net which 

 covers this country. Finally, through a 

 transpacific determination made by the 

 Survey, supplemented by a similar one 



