

Figure [3. I ins drawing vccompanied John Gi I lingham's reporl on the work done in India with K 



invariable pendulum. [Tie value of gravity obtained, direcdy or indiret tlv. in terms of the simple pendulum, 

 is 1 ailed "absolute." < >nce absolute values ol gravity were established a) a ttuml 



use the much simpler "relative" method for the measurement of gravity .11 new stations. 

 Because it has only one knife edge, and does nol involve the adjustments of the convertible pendulum, this 

 one is called "invariable." In use. it is first swung at a station where the absolute value ol gravity has been 

 established, and this period is then compared with its period .0 new stations. Katet developed 



an invariable pendulum in 1819, which was used in England .\nd in Madras, India, in 1821. 



While the British were engaged in swinging the 

 Rater invariable pendulums to determine relative 

 values of the length of the seconds pendulum, or 

 of gravity, the French also sent out expeditions. 

 Capt. de Freycinet made initial observations at Paris 

 with three invariable brass pendulums and one 

 wooden one, and then carried out observations at 

 Rio de Janeiro, (ape of Good Hope, lie de France, 

 Rawak (near New Guinea), Guam, Maui, and vari- 

 ous other places. A similar expedition was con- 

 dinted in 1S22 1S25 by Captain Duperry. 34 



[bid., p. B-88 

 34 Ibid., p. B-94. 



During the years from 1827 to 1840, various types 

 of pendulum were constructed and swung by I 1 

 Baily, a member of the Royal Astronomical Society, 

 who reported in 1832 on experiments in whu h no less 

 than 41 different pendulums were swung in vacuo, 

 and their characteristics determined. 35 In 1836, 

 Baily undertook to advise the American Lt. Charles 

 Wilkes, who was to head the United States Exploring 



I 1 wtas Baily, "On the < orrection of a Pendulum for 



tin Reduction to a Vat uum, Together with Remarks <>u Somi 



Anomalies Observed in Pendulum I " Phil. Trans. 



vol. 122, pp. 399 492. See also Collection de wemoires, 



vol. 4. pp. B ins. B-112, B 115, R IK., and B-ll". 



PAPER 44: niA'lI ( H'MI VI OF GRAVITY PENDULUMS IN THE 1 9TH CENTURA 



317 



