NE WTON AND HUYGENS. 1 1 1 



the time occupied in their descent. Huygens perceived 

 that gravity varies according to the parallels of latitude, 

 and it was not long before he demonstrated, by the number 

 of oscillations which a pendulum of a certain length per- 

 forms in a certain time, that it diminishes in a regular ratio 

 as we approach the Equator, where it reaches its minimum, 

 and that it augments, on the contrary, in due proportion as 

 we approach the Poles, where it must attain its maximum. 

 Strong in this knowledge, and knowing, moreover, that the 

 material molecules, uniformly distributed in the volume of 

 a sphere, act upon a point of its surface as if they were 

 all reunited in the centre of that sphere, Huygens deduced 

 from it the inequality of the equatorial and the polar radius ; 

 he attempted even to determine how much the former ex- 

 ceeded the latter. We know, nowadays, that this difference 

 is 139,670 feet (41,848, 380 41,708,710 feet). 



Newton admits, with Huygens, that the earth bulges out 

 at the Equator and is flattened at the Poles ; that, in a 

 word, it is a spheroid of revolution. He went much farther : 

 he made the precession of the Equinoxes depend upon this 

 flattening; but he did not furnish its mathematical demon- 

 stration. What has been the result? A free skirmishing 

 ground for all opinions. 



While Newton maintained that the form of the earth was 

 that of a spheroid flattened at the poles, as a necessary 

 sequence of the great natural law which bears his name, 

 Jacques Cassini declared himself in favour of an elongated 

 spheroid. The difference between these two illustrious 



