THE RELATIVE FORCE OF GRAVITY AT KEW ARD GREENWICH. 
539 
Kew had not yet been precisely determined, and that special observations were still 
reqiimed for the purpose. 
In 1881 , Colonel Herschel, B.E., was deputed by the Secretary of State for India 
to take pendulum observations at the Greenwich and the Kew Observatories ; also 
at some places in America, with a view to making a connexion with the pendulum 
operations of the Coast and Geodetic Survey of the United States. He employed the 
two pendulums of the Royal Society which had been used in the Indian operations, 
and also a third pendulum of precisely similar construction which had been deposited in 
the Kew Observatory by the Admiralty, the experience already gained in India having 
shown that the employment of a third pendulum was desirable. After completing 
his swings in England and America, he made over the three pendulums to officers of 
the United States’ Survey, who took them round the world, and swung them at 
Auckland, Sydney, Singapore, Tokio, San Erancisco, and finally at Colonel Herschel’s 
station in Washington." 
When the observations came to be finally reduced, it was found that the results 
between Kew and Greenwich by the three pendulums were largely discordant, one 
giving Kew an excess of 1'97 vibrations, another an excess of 1'39, while the third 
gave a defect of 4‘98 vibrations. It was obviously necessary that the pendulums 
should be again swung at the two places, in order to obtain a more satisfactory 
determination of the relative vibration numbers. Fresh swinofs were therefore made 
at Kew in 1888, and at Greenwich in the following year. The operations were 
performed by members of the Observatory staff at each place, Mr. Hollis taking the 
lead and responsibility at Greenwich, under the direction of the Astronomer Royal, 
and Mr. Constable at Kew, under the Superintendent of the Kew Observatory. 
The final results give a vibration number for Kew which differs by less than one 
vibration from that at Greenwich, and may be accepted as very fairly probable. 
• It is the object of the presenc paper to give an abridged account of the above 
operations, both the primary by Colonel Herschel, and the revisionary by Messrs. 
Hollis and Constable.! For this purpose it is necessary, in the first instance, to 
give brief de.scriptions of the pendulums, and of the modus oj^erandi adopted by the 
different observers. 
Description of the Pendulums. 
All three pendulums are of Kater’s Invariable Pattern ; they are made of brass, 
with a steel knife-edge at the head of each pendulum, and they are of very 
nearly the same dimensions. One is numbered 4 and another 11 ; the third has 
* Full details of the operations and their results are given in Appendix No. 14 of the ‘ Report of the 
United States Coast and Geodetic Survey ’ for 1884. 
t Full details of Colonel Herschel’s operations, in manuscript, were made over to the Royal Society 
for record, by the Secretary of State for India; the details of the other operations are recorded in the 
observatories in which they respectively took place. 
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