1890.] Force of Gravity at Kew and Greenwich. 105 



I. " Account of recent Pendulum Operation?; for determining 

 the relative Force of Gravity at the Kew and the Green- 

 wich Observatories." By General WALKER, C.B., F.R.S., 

 LL.D. Received April 15, 1890. 



(Abstract.) 



It is well known that a series of pendulum observations was 

 carried on in India, during the years 1865 to 1873, with two invari- 

 able pendulums, the property of the Royal Society. The Observatory 

 of the Royal Society at Kew was chosen as the base-station of the 

 operations, and the pendulums were swung there before being sent 

 out to India, and again on their return from India. With a view to 

 connecting the observations with those which had already been taken 

 with other pendulums in other parts of the world, it was intended, on 

 the return of the pendulums from India, to swing them at the Royal 

 Observatory at Greenwich, which was a well established pendulum 

 station, observed at by General Sir Edward Sabine, the Russian 

 Admiral Liitke, and others. But when the time arrived for making the 

 observations at the Greenwich Observatory, such extensive prepara- 

 tions were being made there for the equipment of expeditions for the 

 observation of the approaching transit of Venus that no room was 

 available for the pendulum operations. It was, therefore, decided to 

 make the connexion with Kew by swinging at Kew Kater's convertible 

 pendulum, for determining the absolute length of the seconds 

 pendulum, which had been swung 40 years previously at Greenwich by 

 General Sabine. This being done, the length of the seconds pendu- 

 lum at Kew was found to be 0'0027 of an inch greater than the 

 length which had been previously determined at Greenwich, and con- 

 sequently that the daily vibration number was three vibrations 

 greater at Kew than at Greenwich. The difference, however, was 

 far too large to be admissible, as the observatories are nearly in the 

 same latitude, and differ very slightly in height. 



In 1881 Colonel Herschel, R.E., was deputed by the Secretary of 

 State for India to take pendulum observations at the two observa- 

 tories, and at the old pendulum station in London, and also at some 

 stations in America, with a view to improving and strengthening the 

 connexion between the observations in India and those in other parts 

 of the world. On completing his work in America, he handed over 

 the three pendulums which he had employed to officers of the United 

 States Coast and Geodetic Survey, by whom they were taken round 

 the world and swung at Auckland, Sydney, Singapore, Tokio, San 

 Francisco, and finally at Colonel Herschel's terminal station at 

 Washington. 



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