THE FIGURE OF THE EAETH. 21 



by one of the members, at a meeting of the Academy, ac- 

 cording to which the weight of a body must be less at the 

 equator than at the pole, in consequence of the rotation of 

 the earth." He adds doubtfully, that although it would 

 appear from certain experiments made in London, Lyons, 

 and Bologna, as if the seconds-pendulum must be shortened 

 the nearer we approach to the equator; yet on the other 

 hand he was not sufficiently convinced of the accuracy 

 of the measurements adduced, because at the Hague, not- 

 withstanding its more northern latitude, the pendulum 

 lengths were found to be precisely the same as at Paris. 

 The periods at which Newton first became acquainted with 

 the important pendulum results that had been obtained by 

 Richer as early as 1672, although they were not printed 

 until 1679, and at which he first heard of the discovery that 

 had been made by C.assini, before the year 1666, of the' com- 

 pression of Jupiter's disc, have unfortunately not been re- 

 corded with the same exactness, as the fact of his very tardy 

 acquaintance with Picard's measurement of a degree. In an 

 age so remarkable for the successful emulation that distinguished 

 the cultivators of science, and when theoretical views led to 

 the prosecution. of observations, which by their results re- 

 acted in their turn upon theory, it is of great interest to the 

 history of the mathematical establishment of physical as- 

 tronomy, that individual epochs should be determined with 

 accuracy. 



Although direct measurements of meridian and parallel 

 degrees (the former especially in the cast? of the French 

 measurement of a degree 15 between the latitudes 44 42' 

 and 47 30', and the latter by the comparison of points lying 

 to the east and west of the Italian and Maritime Alps), 1 * 

 exhibit great deviations from the mean ellipsoidal figure of 

 the earth, the variations in the amount of ellipticity given 

 by pendulum lengths (taken at different geographical points 

 and in different groups) are very much more striking. The 

 determination of the figure of the earth obtained from the 



15 Delambre, East du Syst. Mttriqiw, t. iii, p. 548. 



16 Cosmos, vol. i, p. 159. Plana, Operations G6od6siques et Astrono- 

 miqucs pour la Mesure dun Arc du ParalUle Moyen, t. ii, p. 847; 

 Carlini in the /emeridi Astronomiche di Milano per Vanno 1842, 

 p. 57. 



