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IX. Experiments to determine the difference in the number of vibrations made by 

 an Invariable Pendulum in the Royal Observatory at Greenwich, and in the 

 house in London in which Captain Kater's experiments were made. By 

 Captain Edward Sabine of the Royal Artillery, Secretary to the Royal Society. 

 Ccmimunicated by the President and Council. 



Read December 11, 1828. 



These experiments were made in compliance with a wish of the Council of 

 the Royal Society, expressed in the following minute, dated December 13th 

 1 827 : " That Captain Sabine be requested to ascertain the difference in the 

 number of vibrations of a pendulum between Mr. Browne's house in London 

 and the Royal Observatory at Greenwich." 



The invariable pendulum employed to accomplish the proposed object was 

 of the usual materials and form, new for the occasion, and numbered 12. The 

 thermometer was the same that I had used in my former pendulum experi- 

 ments ; its graduation is described in the volume containing the account of 

 those experiments, pages 182 — 187- The ball of the thermometer was sus- 

 pended at both stations midway between the knife edge and the centre of the 

 weight of the pendulum. The height of the barometer in the observations at 

 Greenwich was taken by the standard barometer of the Obsei-vatory, which is 

 in a room on the same floor as the pendulum room : in those at London it was 

 taken by Mr. Browne's barometer placed in the room in which the observa- 

 tions were made. Mr, Browne's barometer being compared with the standard 

 of the Greenwich observatoiy, by means of an intermediate portable barometer, 

 was found to require a correction of -|- 0.066 to make it agree with the 

 indications of the Greenwich standard corrected for capillary action. This 

 correction is consequently applied. 



The pendulum was first employed in experiments in Mr. Browne's house 

 from the 17th to the 20th of March inclusive : the rate of Mr. Browne's clock 



m2 



