In 1854, the experiments wen- again undertaken in the 

 1 1. ii urn coalpit, near Sunderland. 1 '' Gravity at the 

 surface was greater than below, because "l the attrac- 

 tion of a shell equal to the depth of the pit. From 

 the density of the shell as determined from spe< imens 

 of rock. Airy found the densit) cil the earth to 

 times greater than that of watei , I - C Mendenhall, 

 in 1880, used a Kater convertible pendulum in an 

 invariable manner to compare values of gravity on 

 Fujiyama and .it Tokyo, Japan. 40 He used a "simple" 

 pendulum of the Borda type to determine the absolute 

 value of gravity .it Tokyo. From the values of gravit) 

 on the mountain and at Tokyo, and an estimate of 

 the volume of the mountain, he estimated the mean 

 density ol the earth as 5. ~7 times greater than thai 

 of water. 

 In 1879, Maj. J. Herschel, RE., stated: 



The years from 1840 to 1865 are a complete blank, if 

 we except Airy's relative density experiments in 1854. 

 I his pause «.is broken simultaneously in three different 

 ways. I\\" pendulums of the Kater pattern wire sent 

 to India; two after Bessel's design were set to work in 

 Russia; and at Geneva, Plantamour's zealous experi- 

 ments with a pendulum of the same kind mark the 

 commencement of an era of renewed activity on the 

 I 1 pean 1 ontinent.*' 



35 G. B. AlRY, "Account of Experiments Undertaken in the 

 Harton Colliery, for the Purpose of Determining the Mean 

 Density of the Earth," Phil. Trans. (1856), vol. 146, p. 2')". 



1 r. C. Mendenhall, "Me isurements of the force of Gravity 

 a lukyo, and on the Summit of Fujiyama," Memoirs of the 

 Science Department, University 0] Tokyo (1881), no. 5. 



•'J. T. WALKER, Account of Operations of Thl ' 

 metricalv Surey of India (Calcutta, 1879), vol. 5, app. no. 2. 



Figure 15. — One of Francos Baily's pendi 



inches long), shown on the left, is now in the 

 possession of the Science Museum, London, and. 

 right, two views of a similar pendulum !;j~'\ inches 

 long) made in the late 19th century 1>\ Edward 

 Kubel, Washington, D.C.. which is no. 316,876 in 

 the collection of the U.S. National Museum. 

 Aiming a large number of pendulums tried by 

 Baily in London (1827-1840), was one which 

 resembles the reversible pendulum superficially, but 

 which is actually an invariable pendulum having 



knife edges at luith ends. 'The purpose was appar- 

 ently economy, since it is equivalent in two separate 



invariable pendulums. This is the type of pendu- 

 lum used on the U.S. Exploring Expedition of 

 1838-1842. It is not known what use was made of 

 the Kubel pendulum. 



1 



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I'AI'ER li: DEVI I <>I'\11 VI (i| GRAVITY I'l Mil I [ MS IN THE 1 '.'TH CENTURY 



319 



