PHYSICAL PROPERTIES OF THE SOIL. 409 



the soil is the rays of the sun. Whatever may be thought of 

 that immense internal fire of liquid .matter supposed to exist within 

 the centre of the globe, and occupying a large portion of it, while 

 we are resting only upon a thin outward crust, yet little of this 

 heat is felt at the surface ; and animal and vegetable life is de 

 pendent upon that magnificent orb which the Creator seems to 

 have placed in the firmament as the emblem of his own inex 

 haustible, impartial, and widely expansive goodness, which bids 

 the sleeping earth, in the spring time, arise as it were from the 

 dead, and put on the habiliments of vegetable splendor and 

 beauty, which fills the luscious vine of summer with its rich 

 clusters, and gilds the autumnal harvest with a beneficent and 

 matchless glory. 



The temperature of the soil is then dependent upon external 

 influences, upon the sun primarily, and the atmosphere as 

 affected by the heat of the sun. This temperature is, of course, 

 affected by the condition of the soil as to wetness or dryness, 

 and somewhat by its inclination and aspect. 



The more direct are the rays of the sun, the stronger the heat 

 produced by thorn ; and the lighter or brighter the surface on 

 which they fall, the less strongly are they absorbed, and the 

 more strongly reflected. In judging of the fertility of a soil, 

 with some persons its color is always matter of consideration ; 

 black soils absorbing heat much more strongly than white or 

 light-colored soils. A rich garden black mould is a great ab 

 sorber of heat. A sandy soil, or soil composed mainly of silex, 

 becomes soon heated, first, from its dryness, the water passing 

 directly through it, and, second, from the smooth surface and 

 crystalline form of the particles of which it is composed ; the 

 heat is increased by being reflected from one side to the other, 

 as in a tin oven. The temperature of a soil is materially affected 

 by its condition .is to moisture or dryness. This is obvious to 

 every one. BUY there is another curious fact in this case, not so 

 generally observed that water is a non-conductor of heat down 

 wards. It wc/jld be difficult to make a kettle of water boil by 

 making a fhv, over it. So the sun s heat upon a wet surface is 

 repelled, fvnrt not transmitted ; and while evaporation may be 

 going on ^t the surface, the lower strata remain cold. The tem 

 perature jf a soil is materially affected by its aspect. Hence 

 soils ] y/g to the south, receiving as they do the more direct 

 35 



