n 







*-*j 



Figure 29. — Tin (.111 i-i \ni 1 1 \i is about 10.7 inches long, and has .1 period ol .8g 



Ii is made of fused quartz which is resistant to the influence of temperature change and to 

 the earth's magnetism. Quartz pendulums are subject to the influence ol electrostatic 

 charge, and provision is made to counteract this through the presence of a radium salt in 

 the case. The bearings are made of Pyrex glass. 



In 1902, Dr. P. Furtwangler M presented the mathe- 

 matical theory of coupled pendulums in a paper in 

 which he referred to Faye's proposal of 1877 and re- 



" P. Furtwangler, "Uber die Schwingungen zweier 

 Pendcl mit ann&hernd gleicher Schwingungsdauer auf gc- 

 meinsamer Unterlage," Siizungsberichte dn ■' ussischen 



haften ai Berlin I 1902) pp. 245-253. 



Peirce investigated the plan of swinging tun pendulums on the 

 same stand (Rtporl of the Superintendent of the l.S. Coast and 

 Geodetic Survey for 1880 81, Washington, 1883, p. 26; also in 

 Charles Sanders Peirce, Collected Papers, 6.273). At a 

 conference <m gravity held in Washington during May 1882, 

 Peirce again advanced the method of eliminating flexure 

 by hanging two pendulums on one support and oscillating 

 them in antiphase ("Report of a conference on gravity deter- 

 minations held in Washington. D.C., in May, 1882," Report 

 of the Superintendent of the U.S. Coast and Geodetic Survey for 1881-82, 

 Washington, 1883, app. no. 22, pp. 503-516). 



ported that the difficulties predicted upon its applica- 

 tion had been found not to occur. Finally, during the 

 gravity survey of Holland in the years 1913-1921, in 

 view ii! instability of supports caused by the mobility 

 of the soil, F. A. \Vning Meinesz adopted Faye's 

 proposed method of swinging two pendulums on the 

 same support." The observations were made with 

 the ordinary Stiickrath apparatus, in which four \ on 

 Sterneck pendulums swung two by two in planes 

 perpendicular to each other. This successful applica- 

 tion of the method — which had been proposed by 

 Faye and had been demonstrated theoretically to be 

 sound by Peirce, who also published a design for its 



PAPER 44: DEVELOPMENT OF GRAVITY PEND1 M MS IN THE 19TH CENTURY 



,0 F. A. Venino MriNtsz, Observations de pendule dans Us 

 Pays- Bas (Delft, 1923). 



337 



