RECENT CONTRIBUTIONS TO OUR KNOWL- 

 EDGE OF THE EARTH'S SHAPE AND SIZE, 

 BY THE UNITED STATES COAST 

 AND GEODETIC SURVEY. 



By C. A. ScHOTT 



THE Survey has just published a 

 quarto volume containing an ac- 

 count of the transcontinental tri- 

 angulations and measurements of an arc 

 of the parallel in latitude 39°. It also has 

 ready for publication the manuscript giv- 

 ing the result of an oblique arc in the east- 

 ern part of the United States. Both are 

 contributions of great length and among 

 the first of their kind in America. 



At first sight it might appear rather late 

 in the history of the Survey to bring out 

 results of the earth'^s figure. But it 

 should be remembered that such measures 

 were not the prime object of the Survey 

 in its early stages of activity, but came 

 about in the natural course of continuous 

 development during nearly tv^o-thirds of 

 a century. What was required was to 

 secure a series of geodetic measures con- 

 sistent within themselves and serving as a. 

 bond binding together the separate detail 

 surveys so as to form ultimately a sys- 

 tematic whole. This requirement de- 

 manded the establishment of extended 

 primary triangulations not only along our 

 coasts, but also as a connecting link across 

 the country from ocean to ocean, to se- 

 cure uniformity of results. The growth 

 of these operations depended of course 

 upon the immediate requirements of the 

 Survey for the production of harbor and 

 coast charts and was subject to the means 

 available from year to year. 



Thus when I state that the first was 

 made between the years 1844 and 1898, 

 and the second between the years 1833 

 and 1898, 1 do not mean that it took fifty- 

 four and sixty-five years respectively to 

 complete the task. Indeed, in either case 



there were many years of interruptions. 

 What these long intervals signify and 

 emphasize, is, that the various opera- 

 tions of the Survey were more urgent- 

 ly required in the production of prac- 

 tical results for immediate use and in 

 a great measure as aid to navigation. 

 For the more technical part of the work 

 the available knowledge of the earth's 

 magnitude was sufficient for the early 

 needs. At the same time it was recog- 

 nized that the measurement of the earth 

 required the same means and methods 

 as that of an extended country, viz., 

 a net-work of primary triangulations and 

 a number of astronomical determinations 

 for latitude, longitude, and azimuth of its 

 points. In time, therefore, sufficient ma- 

 terial would accumulate to direct special 

 attention to this, the highest feature of 

 geodesy. 



After the triangulations had reached 

 hundreds of miles in extent, and the geo- 

 graphical positions had been determined 

 by their development upon the surface of a 

 spheroid representing the shape and size 

 of the earth, it became a matter of im- 

 portance to see that the direct astronom- 

 ical measures for latitude and longitude 

 kept in close accord with the correspond- 

 ing geodetic measures ; thus it came about 

 that in February, 1880, the Survey' 

 changed its first reference spheroid, that 

 of Bessel, for a more suitable one, that of 

 Clarke of 1866. 



When in 1889 the United States, by 

 resolution of Congress, consented to be- 

 come a member of the International Geo- 

 detic Association for the measurement of 

 the earth, the subject of the measures o'f 



