6 



SCIENCE 



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



and placed on one datum are also the many- 

 miles of coast triangulation of the Survey 

 and much of the triangulation executed by 

 the Lake Survey and by the U. S. Engi- 

 neers, until now the system stands without 

 an equal in any nation. 



In the closing years of the last century 

 a new era in geodetic operations by the 

 Coast and Geodetic Survey was begun. 

 The work of the past was searched for the 

 best in instruments and methods, field and 

 office methods were standardized, limits of 

 accuracy were set, and where it seemed ad- 

 visable new methods and instruments were 

 devised to meet the changing conditions of 

 the work. This era may be characterized 

 as a period of great speed and low costs. 



Never before had triangulation been ex- 

 ecuted with such rapidity and with such 

 economy in operations. It is significant 

 that this was attained without a reduction 

 in accuracy, and in fact had the effect of an 

 ultimate increase in accuracy, for, owing to 

 the speed, many more circuits could be 

 added to the network, thus strengthening 

 the whole system. 



As an example of the speed and economy 

 of operation in this last period the Texas- 

 California arc of about 20° is cited. The 

 reeonnoissance on this arc was done by two 

 men in 145 days and the primary observa- 

 tions in a total of 183 days at a cost of $400 

 per station and of $32 per mile of progress. 

 Nearly 50 years were spent on the transcon- 

 tinental arc of 48° with a cost of $2000 per 

 station and $200 per mile of progress. This 

 comparison is not intended to be derogatory 

 to the latter arc, for the work on that arc 

 was the best of any up to that date, and it 

 was only through its work that the economy 

 and speed of the later work was made pos- 

 sible. It. is believed that no extensive arc in 

 any other country equals the Texas-Cali- 

 fornia arc or some of the other recent arcs 

 of the United States, in these respects. 



Since about 1900, practically all of the 

 reeonnoissance and signal building has 

 been in the hands of one man, Signalman 

 Jasper S. Bilby, who as an expert along 

 these lines probably stands unrivaled in the 

 world to-day. 



THE UNITED STATES STANDARD DATUM 



A direct and far-reaching geodetic move- 

 ment of influence, not only to the United 

 States, but also one of great importance to 

 the North American continent, and also to 

 the whole world, was initiated in the adop- 

 tion by the Survey (in 1901) of the United 

 States Standard Datum. It placed the geo- 

 detic work of the Survey on one datum for 

 the correct coordination of the geographic 

 latitudes, longitudes, distances and azi- 

 muths. From the scientist's standpoint it 

 furnished accurate correlation of data for a 

 study of the figure of the earth, of isostasy, 

 and for other related sciences. 



By its adoption, as the Standard Datum 

 for geodetic operations in Canada and Mex- 

 ico, it became a matter of international im- 

 portance and consequently its designation 

 was changed by the Survey in 1913 to that 

 of the "North American Datum." Plans 

 are now under way for carrying the pri- 

 mary triangulation of the United States and 

 Canada to the Yukon, and the prediction is 

 here made, that eventually the fifty miles 

 which separate Alaska from Siberia will be 

 spanned, and a junction be effected with 

 the great systems of Asia, Europe and 

 Africa. Then with the extension from 

 Mexico through Central and South Amer- 

 ica, the data will be available for a "World 

 Datum, ' ' and the final word will have been 

 said in the geodetic work of the earth. 



BASE LINE MEASUREMENTS 



Closely related to, and forming an inte- 

 gral part of the triangulation executed by 

 the Coast and Geodetic Survey, is the meas- 



