ON THE ELLIPTICITY OF THE EARTH. 467 



tures. In restating the general results, therefore, on 

 the present occasion, I have employed O s '44 as the 

 equivalent of 1 Fahr. in reducing both my own and 

 Captain Kater's results to a uniform temperature. The 

 " reduction to a vacuum " is the ordinary buoyancy cor- 

 rection multiplied by the factor 1'65 ; and in the reduc- 

 tion to the sea-level the factor 0-67 has been applied 

 uniformly at all the stations ; the heights were gene- 

 rally small, and the reductions little more than nominal. 

 Whatever errors in the original publication have come 

 to my knowledge subsequently, either by my own recal- 

 culations or by information received from others, have 

 been corrected ; and three stations have been added to 

 the original nineteen, viz. the observatories of Green- 

 wich, Altona, and Paris, which, at the request of the 

 council of the Eoyal Society, I visited subsequently to 

 the polar and equatorial series, employing pendulums of 

 precisely the same form and construction, and pursuing 

 the same processes both of observation and reduction. 

 (Phil. Trans., 1828, art. iv.; 1829, art. ix. ; 1830, 

 art. xviii.) The reductions to the sea-level have been 

 applied to the results in the three memoirs just cited, 

 which reductions were not required in the first instance, 

 because the object then sought was the difference in 

 the rate of vibration at the three observatories from the 

 rate in London. The same coefficients have been em- 

 ployed in the corrections for temperature and buoyancy 

 as at the other stations. On all occasions the inva- 

 riability of the pendulums during the experiments was 

 proved, by bringing them back to the base station, and 

 ascertaining that their rates were unchanged. 



HH 2 



