small so that one can neglect its square, one can 

 determine the length of the seconds pendulum from 

 the times of swing aboul the knife edges by .1 theory 

 which uses the distances of the center of gravity from 

 the respective knife edges. Thus, a role for the posi- 

 tion i>! the center of gravity in the theory ol the 

 reversible pendulum, which had been set forth earliei 

 by Bessel, was discovered independently by Cellerier 

 for the Swiss observers of pendulums. 



In 1866, Plantamour published an extensive memoir 

 "Experiences faites a (ieneve avee le pendule a rever- 

 sion." Another memoir, published in 1872, pre- 

 sented further results of determinations of gravity 

 in Switzerland. Plantamour was the first scientist 

 in western Europe to use .1 Repsold-Bessel reversible 

 pendulum and to work out methods for its employ- 

 ment. 



The Russian Imperial Academy of Sciences ac- 

 quired two Repsold-Bessel pendulums, and observa- 

 tions with them were begun in 1864 by Prof. Sawitsch, 

 University of St. Petersburg, and others. 48 In 1869, 

 the Russian pendulums were loaned to the India 

 Survey in order to enable members of the Surve) to 

 supplement observations with the Kater invariable 

 pendulums nos. 4 and 6 (1821). During the transport 

 of the Russian apparatus to India, the knives became 

 rusted and the apparatus had to he reconditioned. 

 Capt. Heaviside of the India Survej observed with 

 both pendulums at Kcw Observatory, near London. 

 in the spring of 1874, after which the Russian pen- 

 dulums were sent to Pulkowa (Russia) and were 

 used for observations there and in the Caucasus. 



The introduction of the Repsold-Bessel reversible 

 pendulum for the determination of gravity was 

 accompanied l>\ the creation of the first international 

 scientific association, one lor geodesy. In 1861, Lt. 

 Gen. J. J. Baeyer, director of the Prussian Geodetic 

 Survey, sent a memorandum to the Prussian ministei 

 of war in which he proposed that the independent 

 geodetic surveys of the stales of central Europe be 

 coordinated by the creation of an international 

 organization. 4 ' In 1862, imitations were sent to the 

 various German states and to other states of central 

 Europe. The first General Conference of the associa- 

 tion, initially called Die Mittel-Europdische Grad- 

 messung, also L'Associatioi Gf Internationale, was 



Figure ti>. — From a Design Lefti 

 this portable apparatus was developed in 

 1862 by the firm of Repsold in I lambui u. 

 whose foundei had assisted Bessel in the 

 c onsti ui tion ol ins pendulum apparatus 



■ il 1 82G rhl 1 11 minium is CO! 



but differs from Rater's in being gco- 

 illv symmetrical and. lor this 

 reason, Repsold's is usually < ailed "revers- 

 ible." Jusl i" the right "I die pendulum 

 is a standard a ale. 1 the left is .1 

 "vertical comparator" designed by Rep- 

 sold to measure the distance between the 

 knife edges of the pendulum. I 

 this measurement, two mic rometer micro- 

 scopes whii h projei t horizontally through 

 mparator are alternately Incused on 

 the knife edges and on the standard si ale. 



** A. Sawitsch, "Les variations de la pesanteur dans les 

 provinces occidentals de I'Empire russe," Memoirs of the 



/: .-/ Astronomical Society (1872), vol. 39, p. 19. 



4,1 J. J. Baeyer, Cher die Crosse und Figur der F.rde (Berlin, 

 1861). 



PAPER 44: DEVELOPMENT OF GRAVITY PENDULUMS IN THE I'll! CENTURY 

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