538 GENERAL WALKER ON PENDULUM OPERATIONS FOR, DETERMINING 
For the purpose of connecting the Indian operations with those taken by Kater, 
Sabine, Foster, and other observers in various parts of the globe, it was intended 
to swing the Hoyal Society’s pendulums, on their return to England, at the Royal 
Observatory, Greenwich, which was a station of various Important series of operations. 
But when the time arrived, in 1873, it was found that extensive preparations were 
being made in the Observatory for several expeditions which were being outfitted for 
the observation of the apjiroaching transit of Venus, so that no space was left avail¬ 
able for the pendulum operations. It was therefore decided to make the desired 
connexion by swinging Kater’s convertible pendulum, for determining the absolute 
length of the seconds’ pendulum in any latitude, at Kew, as already it had been swung 
by Sabine at Greenwich. This was done by Captain Heaviside, and was the last 
stage of the Indian pendulum operations; the results were published in vol. 5 of the 
‘ Account of the Operations of the Great Trigonometrical Survey,’ Dehra Dun, 1879, 
which gives full details of all the operations, including the swings with the Russian 
pendulums. 
The absolute length of the seconds’ pendulum, in vacuo, at Kew, was found to be 
39‘14008 inches of the British standard yard, in 1873, whereas at Greenwich, Sabine 
had found it to be 39‘13734 inches of Sir George Shuckburgh’s standard scale, in 
1831.* Thus it would seem that a seconds’ pendulum will make about three more 
vibrations in 24 houi-s at Kew than at Greenwich. But the two Observatories are 
nearly in the same latitude, anrl differ very little in height, and are only ten miles 
apart; thus this difference is much too large to be accepted as trustworthy. 
In his work on Geodesy, Colonel Clarke, C.B., R.E., of the Ordnance Survey of 
Great Britain, employs a large number of pendulum determinations in various parts 
of the globe to investigate the figure of the earth. He remarks that the selection of 
Kew, instead of London or Greenwich, as the base station for the Indian series 
of swings, was unfortunate ; and, disregarding the connexion of Kew with Greenwich 
by the two determinations of the length of the seconds’ pendulum, he employs the 
ratio of Madras to London from the observations of Goldingham and Sabine, and 
tliat of Kew to St. Petersburgh, by Heaviside and Sawitsch. Then he makes four 
different combinations of his data, from which he obtains as many values of the 
earth’s elllpticity; and for each value he finds the corresponding system of quantities, 
X, indicating the apparent excess or defect of the observed over the theoretical force 
of gravity at each station of observation ; one combination gives Kew an excess of 
6‘06 vibrations over London ; another gives it an excess of 5’12 vibrations over 
Greenwdch, but reduces the excess over London to 3‘10 vibrations. These figures 
indicate variations in the vibration numbers such as are usually met with on changes 
of latitude of 1 to 2 degrees, and they show that the actual relation of Greenwich to 
* It lias recently been ascertained that very little, if any, of tlie difference can be diie to error of the 
unit of the f^HOCKBURGH scale as compared with the standard yard. See No. 288 of the ‘ Proceedings 
of the Royal Society ’ (vol. 47, 1890, p. 186.) 
