24 COSMOS. 



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

 ing to which the weight of a body must be less at the equa- 

 tor 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 Bo- 

 logna, 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 meas- 

 urements adduced, because at the Hague, notwithstanding 

 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 pendu- 

 lum 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 

 Cassini, before the year 1666, of the compression of Jupiter's 

 disk, have unfortunately not been recorded with the same 

 exactness as the fact of his very tardy acquaintance with 



which I have given in Cosmos, vol. ii., p. 351. The observations made 

 by Richer at Cayenne were not published until 1679, as I have already 

 observed in the text, and therefore not until fully six years after hfg 

 return, and, what is more remarkable, the annals of the Academic des 

 Inscriptions contain no notice during this long period of Richer's im- 

 portant double "observations of the pendulum clock and of the simple 

 seconds-pendulum. We do not know the time when Newton first be- 

 came acquainted with Richer's results, although his own earliest the- 

 oretical speculations regarding the figure of the earth date farther back 

 than the year 1G65. It would appear that Newton did not become 

 acquainted until 1682 with Picard's geodetic measurement, which had 

 been published in 1671, and even then " he accidentally heard of it at 

 a meeting of the Royal Society, which he was attending." His knowl- 

 edge of this fact, as Sir David Brewster has shown (Memoirs of Sir I. 

 Newton, vol. i., p. 291), exerted a very important influence on his de- 

 termination of the earth's diameter, and of the relation which the fall 

 of a body upon our planet bears to the force which retains the moon 

 in its orbit. Newton's views may have been similarly influenced by 

 the knowledge of the spheroidal form of Jupiter, which had been as- 

 certained by Cassini prior to 1666, but was first described in 1691, in 

 the Memoires de I 'Academic des Sciences, t. ii., p. 108. Could Newton 

 have learned any thing of a much earlier publication, of which some 

 of the sheets were seen by Lalande in the possession of Maraldi? 

 (Compare Lalande, Astr., t. iii., p. 335, 3345, with Brewster, Mem- 

 oirs of Sir I. Newton, vol. i., p. 322, and Cosmos, vol. i., p. 165.) Amid 

 the simultaneous labors of Newton, Huygens, Picard, and Cassini, it 

 is often very difficult to arrive, with any certainty, at a just apprecia- 

 tion of the diffusion of scientific knowledge, owing to the tardiness 

 with which men at that day made known the result of their observa- 

 tions, the publication of which was, moreover, frequently delayed by 

 accidental circumstances. 



