HUMPHREYS: METEOROLOGICAL PARADOXES 1 67 



its maximum. That is, the temperature continues to rise for 

 some time, generally 2 to 4 hours, after the sun has crossed the 

 meridian — as the sun begins to descend from its highest point 

 the temperature continues to ascend. 



THE ABSOLUTE MAXIMUM DIURNAL INSOLATION (hEAT SUPPLY) 



IS AT THE SOUTH POLE 



If I is the solar constant, or quantity of solar energy per 

 minute per unit area, normal to the insolation at the limit of the 

 atmosphere, then the total amount Q of solar energy per any 

 consecutive 24 hours, per unit area of a horizontal surface, also 

 at the limit of the atmosphere, is given by the equation 



Q = -^ J(sin (f sin 8H + cos <p cos 5 sin H) 



IT 



in which <p is the latitude of the place in question, d the declina- 

 tion of the sun at the time, and H the hour angle, in radians, 

 between noon and sunrise, or sunset. 



A great deal of interesting information is contained in this 

 equation. The most interesting, perhaps, is the fact that if 

 the value of Q for the equator at the time of the vernal equinox 

 be represented by 1000, then that of the north pole at summer 

 solstice is 1202, and that of the south pole at the corresponding 

 solstice 1284; each being greater than the value of Q at that time 

 for any other place in either hemisphere. The advantage in 

 favor of the south pole is owing to the fact that the earth is then 

 near perihelion, and, therefore, closer to the sun. 



Not only does the absolute maximum diurnal insolation at 

 the limit of the atmosphere occur at the south pole, but, owing 

 to the great elevation of the south polar region, the dryness of 

 its atmosphere and its comparative freedom from dust, so also 

 does the corresponding maximum at the surface of the earth. 



The days, however, of abundant insolation at the poles are 

 comparatively few, nor is this insolation very effective in raising 

 the temperature, owing to the high reflecting power and great 

 heat of fusion of the always prevalent ice and snow. And so 

 it happens that although for a time every year each pole re- 

 ceives more diurnal insolation than does any other place on the 



