86 CAPTAIN SABINE ON THE DIFFERENCE IN THE VIBRATIONS 



being at 62°, the air at 58°.92, the barometer at 29.580, and the mercury 32°. 



The reduction to a vacuum is + 9-92, making 85974.09 vibrations in a 



vacuum at 62°. aaoH^iWiV 



We have thus the vibrations of this pendulum at London and at Greenwich 



as follows. 



London 85973.57 , 



Greenwich 85974.09 



Difference .... 0.52 



Showing an acceleration at Greenwich of 0.52 parts of a vibration per diem. 



Now as the latitude of the Royal Observatory is 2' 28" south of Mr. Browne's 

 house in London, and as its height above the sea is also about 50 feet more, 

 a retardation from these causes combined of about 0.3 of a vibration per diem 

 was to have been expected at Greenwich, instead of an acceleration of 0.52 

 of a vibration. The result appeared therefore sufficiently remarkable to make 

 it desirable to verify it by repetition. 



The pendulum having remained at Greenwich a few days after the experi- 

 ments were completed, the knife edge became slightly corroded with rust, in 

 consequence of the great damp which prevails in the observatory at that season. 

 ITie knife edge having been ground and figured afresh, the pendulum was 

 again conveyed to Portland Place, and the experiments (Appendix D.) made 

 with it on the 8th and 9th of July, the thermometer employed being the same 

 as before, and suspended in a similar manner : the results were as follows. 



•jO.' ;; :.'■ 



London July 1828 ; Experiments with Pendulum 12. 



iirutubn:;'*? 



Barom. Therm. 



Julys. Mean of 7 exp. 29.670 72.07 85955.42 vibrations at 72°. 



July 9. Mean of 7 exp. 29.490 71.73 85955.40 vibrations at 72°. 



29.580 71.9 85955.41 vibrations at 72°. 



The height of the barometer corrected to the standard and reduced to 32° is 

 29.533 inches. lo rioiwrtsdi'i at aoiit-' 



The mean result being that the pendulum, having had its knife edge ground 

 and figured afresh, made 85955.41 vibrations at 72°, equivalent to 85959.71 



