20 COSMOS. 



in October, 1671, and Picard in the description of his mea- 

 surement of a degree of latitude, which appeared in the same 

 year u merely refers to " a conjecture which was advanced 



14 Picard, Mtsure de la Terre, 1671, Art. 4. It is scarcely probabla 

 that the conjecture which was advanced in the Paris Academy even 

 before the year 1671, to the effect that the intensity of gravity varies 

 with the latitude (Lalande, Astronomic, t. iii, p. 20 2668) should have 

 been made by the illustrious Huygens, who had certainly presented 

 his Discours sur la Cause de la Gravite to the Academy in the course 

 of the year 1669. There in no mention made in this treatise of the 

 shortening of the seconds-pendulum, which was being observed by 

 Richer at Cayenne, although a reference to it occurs in the supple- 

 ments to this work, (one of which must have been completed after the 

 publication of Newton's Principia, and consequently later than 1687). 

 Huygens writes as follows: "Maxima pars hujus libelli scripta est, 

 cum Lutetise degerem (to 1681) ad eum usque locum, ubi de altera- 

 tione, quae pendulis accidit e motu Terrse." See also the explanation 

 which I have given in Cosmos, vol. ii, p. 736. 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 his 

 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 

 became acquainted with Richer's results, although his own earliest 

 theoretical speculations regarding the figure of the earth date farther 

 back than the year 1665. It would appear that Newton did not be- 

 come 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 know- 

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

 Neviton, vol. i, p. 291), exerted a very important influence on his deter- 

 mination 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 ascertained 

 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 learnt 

 anything of a much earlier publication, of which some of the sheets 

 were seen by Lalaude in the possession of Maraldi? (Compare 

 Laiande, Astr. t. iii. p. 335, 3345, with Brewster, Memoirs of Sir /. 

 Newton, vol. i, p. 322, and Cosmos, vol. i, p. 156.) Amid the simultan- 

 eous labours of Newton, Huygens, Picard, and Cassini, it is often very 

 difficult to arrive, with any certainty, at a just appreciation of the diffu- 

 sion of scientific knowledge, owing to the tardiness with which men 

 at that day made known the result of their observations, the pub- 

 lication of which, was moreover frequently delayed by accidental cir* 

 cu instances. 



