THE PLANETS. 123 



if, indeed, the Earth's equator were perpendicular to the 

 Earth's orbit, at each part of its surface, even under the 

 poles, the Sun would be in the zenith once in the year, and 

 for a greater or less time, neither rise nor set. The differ- 

 ences of summer and winter under each latitude (as well as 

 the length of the day) would obtain the maximum of opposi- 

 tion. The climates in each part of the Earth would belong, 

 in the highest degree, to those which are called extreme, and 

 which an interminably complicated series of rapidly-changing 

 currents of air could only slightly equalize. If the reverse 

 were the case, or the obliquity of the ecliptic null, if the 

 Earth's equator coincided with the ecliptic, the differences of 

 the seasons and in the length of the days would cease every 

 where, because the Sun would continually appear to move in 

 the equator. The inhabitants of the poles would see it per- 

 petually at the horizon. " The mean annual temperature of 

 each point of the Earth's surface would also be that of each 

 individual day."* This condition has been called an eternal 

 spring, although, however, only on account of the universally 

 equal length of the days and nights. As the growth of 

 plants would be deprived of the stimulating action of the 

 Sun's heat, a great part of those districts which we now call 

 temperate zones would be reduced to the almost always uni- 

 form and not very agreeable spring climate, from which I 

 suffered much under the equator, upon the barren mountain 

 plains (Parairiosf) between 10,659 and 12,837 feet above the 

 level of the sea, situated near the boundary of perpetual snow 

 in the Andes chain. The temperature of the air during the 

 day oscillates there between 4^ and 9 Reaum. (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 development. 

 These speculations belonged especially to Anaxagoras, the 

 Pythagorean school, and to (Enopides of Chios. The pas- 

 sages which give us any information on this point are scanty 

 and indecisive ; however, they show that the development 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 



* Madler, Astronomic, $ 193. 



t Humboldt, De Distributione Geographica Plantarum, p. 104. ( Views 

 of Nature, p. 220 to 223, Bohn's edition.) 



