In 1874, Charles Peirce expressed the desire to be 

 sent to Europe for at least a year, beginning about 

 March 1, 1875, "to learn the use of the new convertible 

 pendulum and to compare it with those of the Euro- 

 pean measure of a Degree and the Swiss and to com- 

 pare" his "invariable pendulums in the manner which 

 has been used by swinging them in London and 

 Paris." 5 " 



Charles S. Peirce, assistant, U.S. Coast Survey, 

 sailed for Europe on April 3, 1875, on his mission to 

 obtain the Repsold-Bessel reversible pendulum or- 

 dered for the Survey and to learn the methods of 

 using it for the determination of gravity. In England, 

 he conferred with Maxwell, Stokes, and Airy con- 

 cerning the theory and practice of research with 

 pendulums. In May, he continued on to Hamburg 

 and obtained delivery from the Repsolds of the pen- 

 dulum for the Coast Survey (fig. 17). Peirce then 

 went to Berlin and conferred with Gen. Baeyer, who 

 expressed doubts of the stability of the Repsold stand 

 for the pendulum. Peirce next went to Geneva, 

 where, under arrangements with Prof. Plantamour, 

 he swung the newly acquired pendulum at the 

 observatory. 58 



In view of Baeyer's expressed doubts of the rigidity 

 of the Repsold stand, Peirce performed experiments 

 to measure the flexure of the stand caused by the 

 oscillations of the pendulum. His method was to set 

 up a micrometer in front of the pendulum stand and, 

 with a microscope, to measure the displacement 

 caused by a weight passing over a pulley, the friction 

 of which had been determined. Peirce calculated 

 the correction to be applied to the length of the seconds 

 pendulum — on account of the swaying of the stand 

 during the swings of the pendulum — to amount to 

 over 0.2 mm. Although Peirce's measurements of 

 flexure in Geneva were not as precise as his later 

 measurements, he believed that failure to correct for 

 flexure of the stand in determinations previously made 

 with Repsold pendulums was responsible for appre- 

 (i.i lil r errors in reported values of the length of the 

 seconds pendulum. 



The Permanent Commission of Die Europdische 



67 Eisele, op. cit. (footnote 55), p. 311. 



68 The record of Peirce's observations in Europe during 1875- 

 76 is given in C. S. Peirce, "Measurements of Gravity at 

 Initial Stations in America and Europe," Report of the Superin- 

 tendent of the Coast Survey for 1875-76 (Washington, 1879), pp. 

 202-337 and 410-416. Peirce's report is dated December 13, 

 1878, by which time the name of the Survey had been changed 

 to U.S. Coast and Geodetic Survey. 



Gradmessung met in Paris, September 20-29, 1875. 

 In conjunction with this meeting, there was held on 

 September 21 a meeting of the Special Commission 

 on the Pendulum. The basis of the discussion by the 

 Special Commission was provided by reports which 

 had been submitted in response to a circular sent 

 out by the Central Bureau to the members on 

 February 26, 1874/" 



Gen. Baeyer stated that the distance of 1 meter be- 

 tween the knife edges of the Prussian Repsold-Bessel 

 pendulum made it unwieldy and unsuited for trans- 

 port. He declared that the instability of the stand 

 also was a source of error. Accordingly, Gen. Baeyer 

 expressed the opinion that absolute determinations 

 of gravity should be made at a control station by a 

 reversible pendulum hung on a permanent, and there- 

 fore stable stand, and he said that relative values of 

 gravity with respect to the control station should be 

 obtained in the field by means of a Bouguer invariable 

 pendulum. Dr. Bruhns and Dr. Peters agreed with 

 Gen. Baeyer; however, the Swiss investigators, 

 Prof. Plantamour and Dr. Hirsch reported in defense 

 of the reversible pendulum as a field instrument, as 

 did Prof, von Oppolzer of Vienna. The circumstance 

 that an invariable pendulum is subject to changes in 

 length was offered as an argument in favor of the 

 reversible pendulum as a field instrument. 



Peirce was present during these discussions by the 

 members of the Special Commission, and he reported 

 that his experiments at Geneva demonstrated that 

 the oscillations of the pendulum called forth a flexure 

 of the support which hitherto had been neglected. 

 The observers who used the Swiss and Austrian 

 Repsold pendulums contended, in opposition to 

 Peirce, that the Repsold stand was stable. 



The outcome of these discussions was that the 

 Special Commission reported to the Permanent Com- 

 mission that the Repsold-Bessel reversible pendulum, 

 except for some small changes, satisfied all require- 

 ments for the determination of gravity. The Special 

 Commission proposed that the Repsold pendulums 

 of the several states be swung at the Prussian Eichung- 

 samt in Berlin where, as Peirce pointed out, Bessel 

 had made his determination of the intensity of gravity 

 with a ball pendulum in 1835. Peirce was encouraged 

 to swing the Coast Survey reversible pendulum at the 

 stations in France, England, and Germany where 



59 Verhandlungen der vom 20 bis 29 September 1875 in Pais I 

 ten Permanenten Commission der Europaischen Gradmessung (Berlin, 

 1876). 



324 



BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



