SCIENTIFIC AGRICULTURE. 17-"> 



where sunshine is deficient, and in fields which bavo a northern 

 aspect 



Power of retaining heat. As heat always tends to seek an 

 equilibrium, it follows that after the sun has disappeared, and 

 his rays cease to shine on a particular part of the earth, the 

 amount of heat which it has absorbed above that of the air is 

 gradually given off again to the latter, until their temperature 

 is equal, or until the air becomes the coldest, as in frosty 

 nights. A peat soil cools more quickly than clay, and clay 

 more quickly than sand. This difference must have an influ- 

 ence on the growth of crops. In cold, wet soils, the property 

 of radiating heat slowly compensates in some degree for the 

 injury done (o plants by these conditions. It also prevents the 

 formation of dew and frost, as soon as would otherwise be the 

 case. On the contrary, soils which radiate heat faster promote 

 the formation of dew by becoming cooled below the dew point 

 sooner, and in this way compensate in some small degree, for 

 deficiency of rain. 



The absorbing, as well as radiating power of the soil, may 

 be increased by a top dressing of soot, charcoal, muck, or some 

 dark colored manure. The principle of absorption and radia- 

 tion as dependent upon color, holds true in relation to plants, 

 as well as to soils: and, if all other conditions are favorable, 

 the light colored, (white straw,) crops should be cultivated on 

 dark colored soils, and the dark colored, (green straw,) crops 

 on the light colored soils* 



The study of the mechanical and physical properties of 

 soils is of more importance than has generally been supposed. 

 These have now been discussed as fully as limits would admit, 

 and we conclude the subject by stating finally, what are the 

 ultimate uses and relations of the soil to plants. 



* This idea is original with the author, so far as he knows : whether 

 of any value or not, others may judge and decide. 



