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1819.] Proceedings of Philosophical Societies. 139 



Article X. 



Proceedings of Philosophical Societies. 



ROYAL SOCIETY. 



June 10. — A paper, by Capt. H. Kater, was begun, entitled 

 ' An Account of Experiments for determining the Length of the 

 Pendulum vibrating Seconds at the principal Stations of the 

 trigonometrical Survey." 



June 17. — Capt. Kater's paper was continued. 

 June 24. — Capt. Kater's paper was concluded. The author 

 commenced by noticing the reasons which induced him to under- 

 take the experiments forming the object of his present report ; 

 and afterwards proceeded to describe the apparatus employed. 

 The operations at each station were then minutely detailed, the 

 results stated at length, and illustrated by numerous tables. 



For the latitude of London, the length of the pendulum vibrat- 

 ing seconds on the scale forming the basis of the trigonometrical 

 survey was stated to be 



39-13722inches. 



For the latitude of Unst 39-1 6939 



Portsoy 39-15952 



Leith-fort 39-15347 



Clifton 39-14393 



Arbury Hill 39-14043 



Shanklin Farm . , . . 39-13407 



The calculations of the latitude of each of these stations was 

 then given at length. The latitude of Arbury Hill, which has 

 been supposed to be erroneous, was found by Capt K. to be 

 correct. The whole was concluded with some observations on 

 the figure of the earth 



It appeared from this interesting report, to which it is impos- 

 sible to do justice by merely hearing it read, that, excepting the 

 allowance for the height above the level of the sea, the error in 

 the vibrations of the seconds pendulum at any particular station 

 did not amount to T '^th of a vibration, which is about equal to the 

 400,000 part of the length, consequently that the amount of the 

 gravitation could be determined to this degree of accuracy. 

 Now this is so near as to indicate the different degrees of density 

 of the materials constituting the substrata of the different stations 

 in a country selected for experiment. Hence Capt. K. concluded 

 that minute differences in density, indicated by the pendulum, 

 are often to be referred to irregularities of attraction : thus the 

 sudden increase of gravitation at Arbury Hill was supposed by 

 the author to be produced by the granite existing in Mount 

 Sorrel, in Leicestershire. 



Capt. Kater stated that he had learned with pleasure that 

 M. Biot's results (the details of which are not yet published"), 



