828 SPECIAL RESULTS IN THE URANOLOGICAL 



this element is of the most essential importance in deter- 

 mining " astronomical climates" i. e. the temperature of 

 the globe, so far as that temperature is a function of the 

 altitude attained by the sun at noon, and of the length of 

 the time during which the sun remains above the horizon. 

 With a considerably greater obliquity of the ecliptic, or 

 supposing the terrestrial equator to be perpendicular to the 

 Earth's orbit, every place on the Earth would once a year 

 have the sun in its zenith, even under the poles, and for a 

 longer or shorter time would not see the sun rise. Under every 

 latitude the difference of summer and winter (as well as of 

 the length of day) would reach the maximum of contrast. 

 In every part of the Earth the climates would be in the 

 highest degree of the description which we call " excessive " 

 their extreme character would be only very slightly modified 

 by the extraordinarily complicated series of rapidly changing 

 currents of air which would be produced. In the reverse 

 case, that of the obliquity of the ecliptic being null, or the ter- 

 restrial equator coinciding with the ecliptic, the difference of 

 seasons and of length of day would everywhere cease, because 

 the sun's apparent course would be uninterruptedly in the 

 equinoctial line. The inhabitants of the poles would never 

 cease to see the sun on the horizon. " The mean annual 

 temperature of any point on the Earth's surface would also 

 be that of each day in the year at the same place" ( 528 ). 

 Such a state of things has been called one of perpetual spring, 

 though the constant equality of day and night seems the 

 only reason for the term. If it existed on the Earth, a 

 great part of the regions which we now call the temperate 

 zone, being deprived of the degree of summer heat which 

 now stimulates and supports vegetation, would be transferred 



