THE PLANETS. 451 



Earth, in as far as this is a function of the meridian altitude 

 attained by the Sun and the duration of its continuance 

 above the horizon. If the obliquity of the ecliptic were 

 great, or 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 

 differences of summer and winter under each latitude (as 

 well as the length of the day), would attain the maximum of 

 opposition. 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 everywhere, because the Sun would continually appear 

 to move in the equator. The inhabitants of the poles would 

 see it perpetually at the horizon. " The mean annual tem- 

 perature 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 uniform and not very agreeable spring climate, from 

 which I suffered much under the equator, upon the barren 

 mountain plains (Paramos* 7 ) between 10,659 and 12,837 feet 

 above the level of the sea, situated near the boundary of 



Madler, Astronomic. 193. 



** Humboldt, De Distributions geographica Plantarum* 

 p. 104. ( Vieics of Nature, p. 220 to 223, Bonn's edition.) 

 VOL. iv. M 



