452 COSMOS. 



perpetual snow in the Andes chain. The temperature of the 

 air during the day oscillates there between 4^ and 9 

 Keaum. (42 and 52-25 Fahr.) 



Grecian antiquity was much occupied with the obliquity 

 of the ecliptic, with rough measurements, conjectures as to its 

 variability, and the influence of the inclination of the Earth's 

 axis upon climate, and the luxuriance of organic develop- 

 ment. These speculations belonged especially to Anaxagoras, 

 the Pythagorean school, and to (Enopides of Chios. The 

 passages which give us any information on this point are 

 scanty and indecisive; however, they show that the deve- 

 lopment of organic life and the origin of animals were 

 considered to have been simultaneous with the epoch in 

 which the axis of the Earth first commenced to be inclined, 

 which also altered the inhabitability of the planet in particular 

 zones. According to Plutarch, De Plac. Philos. ii. 8, 

 Anaxagoras believed " that the world, after it had come into 

 existence and produced from its womb living beings, had of 

 itself inclined towards the south." In the same regard, 

 Diogenes Laertius says of the Clazomenier, "the stars had 

 originally projected themselves in a dome-like layer, so that 

 the pole appearing at any time was vertically over the Earth ; 

 but that afterwards they assumed an oblique direction." The 

 origin of the obliquity of the ecliptic was considered as a 

 cosmical event. There was no question respecting a subse- 

 quent progressive alteration. 



The description of the two extreme, therefore opposite, 

 conditions to which the planets Uranus and Jupiter approxi- 

 mate most closely, is suited to call to mind the variations 

 which the increasing or decreasing obliquity of the ecliptic 

 would produce in the meteorological relations of our planet, 

 if these variations were not comprised within very narrow 

 limits. The knowledge of these limits, the subject of the 

 great works of Leonhard Euler, Lagrange, and Laplace,, may 



