I2(J PHILOSOPHICAL TRANSACTIONS. [ANNO 1737. 



have a motion on its axis, as is well known it has in 24 hours ; this spherical 

 figure must have been changed into that of a spheroid, flatted at its poles, in 

 which the degrees on the meridian must be greater towards the poles, than near 

 the equator. 



Sir Isaac confirms this hypothesis of the earth's figure, by observations of the 

 diminution of the simple pendulum on approaching the equator : to which Dr. 

 Pound adds the analogy the earth has with some of the other planets, as Jupiter, 

 which sometimes appears oval, its least axis being that about which it makes its 

 revolution. 



This opinion of Sir Isaac has likewise been maintained by Mr. Huygens, 

 though with some small difference. But in J 691, Mr. Eisenschmid having 

 compared the measurements of the earth made in different latitudes, as that of 

 Father Riccioli in Italy, of Mr. Picart in France, and of Snell in Holland; and 

 having found that the degree, which resulted from those different measure- 

 ments, continued to decrease in approaching the poles, which is quite the con- 

 trary of what follows from the earth's figure supposed by Sir Isaac and Huygens, 

 Mr. Eisenschmid was therefore of opinion, that the earth was longer at the 

 poles. 



This opinion of Mr. Eisenschmid was afterwards confirmed by the late Mons. 

 Cassini, in the observations of the meridian of Paris. For in 1701, having 

 carried on these operations to the Pyrensean mountains, which is a space of 

 above 7+ degrees, he found that as he advanced to the south, these degrees in- 

 creased -5-i-5^ part, or Tl toises each degree. 



Since the meridian of Paris was, in 1 7 1 8, carried on northward to the sea, 

 M. Cassini, the son, found on comparing more than 8 degrees, which this 

 meridian contains from sea to sea, that the increase, going northward, was but 

 from 60 to 61 toises each degree; as may be seen in the large treatise published 

 in a separate volume, as a sequel to the memoirs of the Royal Academy of 

 Sciences of Paris for the year 17I8. These reasons did not hinder Sir Isaac 

 from persisting in his first opinion of the figure of the earth flatted at the poles, as 

 appears in the 2d and 3d editions of his Principia, published in 1713 and 1726: 

 and it is very surprising, that by this very figure of the earth he demonstrates a 

 certain motion it has, to explain in the Copernican system the precession of the 

 equinoxes, or the apparent motion of the fixed stars in longitude. Sir Isaac 

 finds the inequality of the degrees on the meridian, in so little an extent as that 

 of France, not sensible enough to be possibly determined by immediate obser- 

 vations ; and he is of opinion, that we ought more to rely on the observations 

 of the simple pendulum, and on the other principles which he has built upon, 

 to conclude the earth flatted at the poles. 



