288 SOILS. 



the result of heat conditions, it is proper to discuss from the 

 outset the origin and mode of action of heat. 



TEMPERATURE. 



The temperature of stellar space outside of the atmosphere 

 is known to be very low. The increasing cold as we ascend to 

 greater heights, is a fact familiar to all. Langley has calcu- 

 lated upon the basis of observations made at the summit and 

 foot of Mount Whitney in California, that the temperature of 

 space lies near 200 Cent. (360 F.) below the freezing point 

 of water; and this would be the temperature near the Earth's 

 surface, were it not for the surrounding atmosphere. The lat- 

 ter absorbs but a small amount of the sun's direct heat rays 

 (which are of high intensity), as they penetrate it to the 

 Earth's surface. But as the earth's surface is warmed, the 

 heat rays of low intensity which it emits cannot pass back 

 through the atmosphere to the sun or to outer space ; they are 

 " trapped," as it were, by the dense air resting near the earth's 

 surface, which is then warmed partly by the radiation from, 

 partly by direct contact with, the soil. It is to the existence of 

 our atmosphere, then, that the possibility of our animal and 

 vegetable life in their present form is due; and a decrease of 

 the trapping effect on the sun's heat rays makes itself quickly 

 felt when ascending, either in balloons or on high mountains. 

 Moreover, it is well known to mountain climbers that at great 

 elevations the sun's heat is extremely intense at noon ; even 

 though the temperature may fall to the freezing point at night, 

 owing to the failure of the thin air to prevent the radiation 

 back into space of the heat absorbed during the day. On the 

 high plateaus of the Andes and of Asia, therefore, very ex- 

 treme climates prevail, on account of the great range of tem- 

 perature between day and night. 



Ascertainment and Presentation of Temperature-Conditions. 

 The proper understanding of the temperature conditions of 

 any locality or region is by no means a simple matter. Shall 

 we study the daily, monthly, or annual changes of temperature, 

 or the means deduced from either or all of them, in order to 

 gain a clear insight into the climatic conditions that control 

 crop production and health conditions? 



