METEOROLOGICAL PARADOXES HUMPHREYS. 193 



it is obvious, from the preliminary explanation above, that the mini- 

 mum temperature can not occur until some time after winter solstice, 

 or when the days have again grown longer, and that the delay must 

 depend on latitude, nature of surface, and a number of other factors. 



The date of this minimum temperature is still further delayed, in 

 many places, by the trend of warm ocean currents and the warmer 

 surface drifts toward the higher latitudes, and by on-shore winds. It 

 is also affected, though probably but slightly, by the thermal effects of 

 freezing, thawing, evaporation, and condensation. 



The storage of heat in the earth while the days are long, its gradual 

 delivery back to the surface while the daily supply from the sun is 

 comparatively small, and the poleward drift of warm water at all 

 seasons, together produce, as explained, the paradoxical result so 

 admirably expressed by the proverb : 



As the days grow longer 

 The cold grows stronger. 



AS THE NIGHTS GROW LONGER THE HEAT GROWS STRONGER. 



It will be recognized at once that this paradox is onfy the counter- 

 part of the one just discussed, and that it must also have substantially 

 the same explanation. 



As the days continue to grow longer after the time of minimum 

 temperature, it is clear that from then on for several months the 

 earth's gain of heat must be at a faster rate than its loss — that, in 

 terms of the above explanatory hypothesis, the effective temperature 

 of the shell is T and that of the inclosed object T — t. Under these 

 conditions the earth, because of its large but finite heat capacity, 

 must continue to slowly grow warmer until the incoming radiation 

 has become less; that is, until the nights have grown perceptibly 

 longer. 



This lag, the lag of maximum temperature after the summer sol- 

 stice, is also, like the lag of minimum temperature after the winter 

 solstice, a function of location; generally least in the interior of 

 continents and greatest on islands and near coasts whose prevailing 

 winds are on-shore. 



AS THE SUN DESCENDS THE TEMPERATURE ASCENDS. 



By this paradoxical expression it is only meant to state tersely the 

 well-known fact that the warmest time of the day is not when the sun 

 is on the meridian, or when insolation is greatest, but sometime in the 

 afternoon when the sun has descended considerably from its maxi- 

 mum elevation. As everyone knows, night cooling reaches its great- 



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