L02 Bowie — Recent Gravity Work in the United States. 



Geodetic Work. The necessary investigations and experi- 

 mental work were done by former Assistant William H. 

 Burger, in the fall of 1907, assisted by Mr. Hayford and Mr. 

 E. G. Fischer, the Chief of the Instrument Division. The 

 instrument was made in 1908 at onr office. The interferom- 

 eter has been used successfully during the past five seasons in 

 the field. A monograph on this subject, written by Mr. 

 Burger, appears as Appendix 6 of the report of the Superin- 

 tendent for the fiscal year 1909-10, which is now available for 

 distribution. 



Previous to the year 1909 the relative intensity of gravitation 

 had been determined at 47 stations in the United States : 37 

 were established by former Assistant G. R. Putnam, 3 by 

 Assistant Edwin Smith, 1 by former Superintendent Dr. T. C. 

 Mendenhall, and 1 by the late Assistant E. D. Preston. One 

 of the 47 is the station at the Coast and Geodetic Survey 

 Office, and another at the Smithsonian Institution.* 



Each of the stations is referred to the pendulum pier at the 

 Coast and Geodetic Survey Office as the base. The value for 

 this station is 980'Hl dynes and was determined relatively in 

 1900, using Potsdam, Germany, as the base.f The value at 

 Potsdam was determined by the absolute method, using the 

 reversible pendulum. Additional gravity work was taken up 

 in 1909. It was started under the direction of Mr. Hayford, 

 as Inspector of Geodetic Work, with Mr. Burger in immediate 

 charge of the party making the observations. When Mr. 

 Hayford left the Survey in the fall of 1909, the work was 

 continued under the speaker. Mr. Burger has established 35 

 stations, Assistant H. D. King 21 stations, and the field work 

 is now being done by Aid T. L. Warner, who will make obser- 

 vations at from 15 to 20 stations. 



The field work during the present campaign will end at the 

 close of this calendar year, by which time the value of the 

 intensity of gravitation will have been determined at about 75 

 stations during the three years, 1909-11. These, with the 47 

 old stations, make a total of about 120. In making the selec- 

 tions, uniformity of distribution has been the principal aim, 

 but consideration has also been given geology, elevation, 

 erosion, and deposition of material. With the exception of 

 the introduction of the use of the interferometer in measuring 

 the flexure, the methods of conducting the recent work are 

 practically those used by former Assistant G. R. Putnam.;}; 



Three pendulums, constituting a set, were used at each 

 station. 



*The results are published in Appendix 15, Eeport for 1891 ; Appendix 1, 

 Report for 1894 ; Appendix 6, Report for 1897 ; Appendix 4, Report for 1899. 

 \ See p. 355, Appendix 5, Eeport for 1901. 

 \ See Appendix 1, Eeport for 1894. 



