60 THE FIRST BOOK OF FARMING 



CONDITIONS WHICH INFLUENCE SOIL TEMPERATURE 



It will be noticed that the dry soils are warmer 

 than the wet ones. Why is this? Scientists tell us 

 that it takes a great deal more heat to warm water 

 than it does to warm other substances. Therefore 

 when soil is wet it takes much more heat to warm 

 it than if it were dry. 



It will be seen that of the dry soils the humus is 

 the warmest. Why? 



Experiment. Take two thermometers, wrap the 

 bulb of one with a piece of black or dark colored 

 cloth and the bulb of the other with a piece of white 

 cloth, then place them where the sun will shine on 

 the cloth covered bulbs. The mercury in both ther- 

 mometers will be seen to rise, but in the thermom- 

 eter with the dark cloth about the bulb it will rise 

 faster and higher than in the other. This shows 

 that the dark cloth absorbs heat faster than the 

 white cloth. In the same manner a dark soil will 

 absorb heat faster than a light colored soil ; there- 

 fore it will be warmer if dry. 



Why was the dry clay warmer than the dry sand ? 



Because its darker color helped it to absorb heat 

 more rapidly than the sand, and, as the particles 

 were smaller and more compact, heat was carried 

 into it more rapidly by conduction. 



Why were the wet humus and clay cooler than 

 the wet sand? 



As they were darker in color and the clay was 

 more compact than the sand, they must have ab- 



