NOTES. V 



years after his return, and, what is more surprising, no notice of his important 

 double observation, of the clock pendulum and of a simple second's pendulum, 

 occurs in the Proceedings of the Acade'mie des Inscriptions during this long in- 

 terval. We do not know when Newton, whose earliest theoretical speculations 

 on the figure of the Earth were antecedent to 1665, first became aware of 

 Eicher's results. Picard's arc measurement, although published in 1671, only 

 came very late (1682), and indeed accidentally, in conversation at a meeting of 

 the Royal Society, to Newton's knowledge. It exercised, as Sir David Brewster 

 has shown (Life of Newton, p. 152), an exceedingly important influence on his 

 determination of the Earth's diameter and the relation of the fall of bodies on our 

 planet to the force which governs the moon in her course. We may suppose a 

 similar influence to have been exercised on Newton's ideas by the knowledge of 

 the elliptic figure of Jupiter, which was recognised by Cassini previous to 1666, 

 but first described by him in 1691, in the Me'moires de 1' Academic des Sciences, 

 t. ii. p. 108. May Newton have known anything of an earlier publication, some 

 sheets of which were seen by Lalande in Maraldi's hands ? (Compare Lalande, 

 Astr. t. iii. p. 335, 3345, with Brewster's Life of Newton, p. 162, and Kos- 

 mos, Bd. i. S. 420, Anm. 99; English edition, p. xlii. Note 129.) In the con- 

 temporaneous labours of Newton, Huygens, Picard, and Cassini, the great delay 

 in publication which was then customary, and the frequent accidental delays in 

 communications, render it very difficult to arrive at any well-assured traces of 

 the transmittance or exchange of scientific ideas. 



( 15 ) p. 26. Delambre, Base du Syst. me'trique, t. iii. p. 548. 



( 16 ) p. 26. -Kosmos, Bd. i. S. 422, Anm. 3 (English edition, p. xlv. Note 

 133); Plana, Ope'rations geode'siques et astronomiques pour la Mesure d'un Arc 

 du Parallele moyen, t. ii. p. 847 ; Carlini, in the EfFemeridi astronomiche di 

 Milano per 1'anno 1842, p. 57. 



( 17 ) p. 26. Compare Biot, Astronomic physique, t. ii. (1844) p. 464, with 

 Kosmos, Bd. i. S. 424, end of Anm. 3 (English edition, Note 133), and Bd. iii. 

 S. 432 (English edition, p. 310), where I notice the difficulties which the com- 

 parison of the planet's time of rotation with its observed ellipticity presents. 

 Schubert (Astron. Th. iii. S. 316) had called attention to this difficulty. Bessel, 

 in his memoir " Ueber Haass und Gewicht," says expressly that " the assump- 

 tion of gravity remaining always the same at a place where it has been observed, 

 appears in some degree uncertain, from the knowledge we have acquired of the 

 slow changes of level of considerable portions of the Earth's surface." 



( 18 ) p. 26. Airy, in his excellent Memoir on the Figure of the Earth (Encycl. 

 Metrop. 1849, p. 229), counted, in the year 1830, fifty different stations at which 

 well-assured results had been obtained ; and fourteen others where the results 



