226 NATURE AND PROPERTIES OF SOILS 



the short ultra-violet rays, through the so-called light wave 

 series to the long infra-red rays, the latter possessing the 

 greatest heat possibilities. The insolation of energy received 

 at the upper limits of the earth's atmosphere varies with the 

 season and with the position chosen. 1 



Due to the gases of the atmosphere and especially to clouds 

 and dust, only a small portion of the total insolation actually 



ATMOSPHERE 



RAD/ANT 

 ENERGY 



ABSORPTION 



REFLECTION 



REFRACT/OR, 



EVAPORATION 



RADIATION 



CONDUCTION 



REFLECTION 



SOIL 



CONDUCTION 

 CONVECTION 

 ORGANIC DECAY 



/-ABSORPTION 

 _ COLOR, 5LORE 

 2- SPECIFIC HEAT 

 TEXTURE 

 STRUCTURE 

 MOISTURE 

 3- MOVEMENT 

 A- LOSS OF HEAT 



rise or 



TEMPERATURE 





Fig. 41. — A diagram showing the heat relations of soil. 



does work either on the land or water surfaces of the earth. 

 The atmosphere and its impurities probably deflect on an 

 average more than three-fourths of the insolation by absorp- 

 tion, reflection, and refraction. Little or none of .such energy 

 ever reaches the earth itself. Clouds and dust play an im- 

 portant role in such interception, affecting to a marked degree 

 the energy received at any particular location. Part of the 

 original insolation reaching the earth 's surface is immediately 

 reflected and is lost as radiant energy, having undergone no 



1 The earth and its atmosphere receives but one two-billionth of the 

 sun's energy. Cm such a trifling proportion of the sun's energy depend 

 almost all of the earth's activities. 



