Figure of the Earth. 151 



were employed either in performing geodetic operations, or in 

 calculating their results. We would not charge these distin- 

 guished philosophers with unfairness ; they are far above any 

 such suspicion ; but would merely remark the singular coincidence 

 that has from time to time been found, between the deductions 

 obtained by means of the pendulum, and by the actual measure of 

 arcs, when used to confirm each other. The French commission, 

 who reported the Systime Metrique, inferred an ellipticity of -g^g-. 

 by comparing the degrees measured in France with that mea- 

 sured in Peru; and this oblateness is employed by them as the 

 foundation of that system, so beautiful in theory. Laplace, who 

 was one of that commission, calculated the compression of the 

 earth, from 15 lengths of the pendulum, measured at different 

 places, and inferred that it was-g-^. This, if accurate, might have 

 fairly been received as a strong confirmation ; but on examina- 

 tion of his calculation, as given in the third book of the Mecha- 

 nique Celeste, an error in taking out a logarithm will be detected ; 

 and correcting this mistake, the deduced ellipticity, by his method 

 of calculation, would be increased to -g-j ? . Since that period, 

 and when the compression deduced from the measure of more dis- 

 tant arcs, became T ^ ; and that which agrees with the inequali- 

 ties in the lunar motion, arising from the shape of the earth, is 

 supposed to be about ^^ ; the same illustrious author, by admit- 

 ting the new observations of Biot and Arago, infers from the 

 general combination of pendulum experiments, an ellipticity ofg-f^. 

 No better proof can be afforded than this, of the facility with 

 which the few observations that had been made, before the pen- 

 dulum was taken up by Great Britain, as a distinct and independ- 

 ent method, could be made to agree with any hypothetical oblate- 

 ness of the terrestrial spheroid, when examined merely for the pur- 

 pose of confirming, or disproving the calculations, whose data are 

 derived from other sources. It is now time that the pendulum 

 should assume the rank of an independent measure of the rela- 

 tion between the two diameters of the earth; and the credit is 

 due to Captain Sabine, of having been the first experimental phi- 

 losopher, who has distinctly asserted its equal claim, as well as 

 proved by his experiments its right to be so considered. His ex- 

 periments have, in fact, done more than place it on an equality, 

 as present authority, with the measurement of terrestrial degrees : 

 in his hands, it has become the only method of deducing the fi- 

 gure of the earth, which, as yet, has given a precise and determi- 

 nate result. 



We fully concur in Captain Sabine's opinion, that the satisfac- 

 tory and conclusive nature of the result, which the pendulum has 

 afforded, when the experiments with it have thus been duly and 

 sufficiently extended, presents a strong ground of encouragement 



