1 86 Putnam — Results of Pendulum Observations. 



Art. XIX. — Results of Recent Pendulum Observations /* 

 by G-. R. Putnam. 



Some additional relative measurements of the force of 

 gravity were made by the Coast and G-eodetic Survey during 

 the summer of 1895. This work was done at certain primary 

 telegraphic longitude stations of the Survey, and as it was 

 incidental to the longitude work, the points were not selected 

 with especial reference to their value as gravity stations. 

 Notwithstanding this fact and their small number, they happen 

 to be so located as to be of interest in several ways, and it is 

 therefore thought desirable to give this preliminary summary 

 of the results. The observations were made with the Menden- 

 hall half-second pendulums, and the instruments and methods 

 used were almost identical with those employed by the writer 

 at 26 stations in 1894 and already fully described. \ About 

 the only change was in the use of two knife-edges instead of 

 one. For the purpose of further insuring the independence of 

 the pendulums, two pendulums were always swung upon one 

 knife-edge and the third upon the second knife-edge. The 

 pendulums were swung at the base station in Washington in 

 January, 1895, and again after the return from the south in 

 August; the mean corrected period of the three was in Janu- 

 ary ■•5007121, and in August s '5007113. This difference may 

 in part be due to some slight uncertainty in the temperature 

 coefficient. To compare these periods with those obtained by 

 the same pendulums at Washington in 1894, a small correction 

 of + ••0000004 must be added to these means to allow for 

 the fact that one pendulum was swung on a different knife- 

 edge, which diminished the period of that pendulum. When 

 this comparison is made there is found a slight but un- 

 important diminution in the average period, as seems to be the 

 general tendency of the effect of use on pendulums. Because 

 of the fact that Austin, Texas, formed one end of several of 

 the longitude lines, opportunity was there afforded to make 

 some additional tests in regard to the agreement of repeated 

 but entirely independent determinations. A full series of 

 observations was made at the end of April in a very favorably 

 located basement room in the granite Capitol of the state of 

 Texas. The apparatus was then used at Laredo and Galveston 



* Published by permission of the Superintendent of the U. S. Coast and 

 Geodetic Survey. Head before the Philosophical Society of Washington, Jan. 18, 

 1896. 



f Report U. S. Coast and G-eodetic Survey for 1894, Appendix No. 1; also 

 " Results of a trans-continental series of gravity measurements: " Bulletin Philo- 

 sophical Society of Washington, vol. xiii, p. 31. 



