PRACTICAL AGRICULTURE. 205 



289. This should be explained! Whenever water 

 evaporates, it carries off a great deal of heat. If a 

 kettle of water is heated to the boiling point, 212^, it 

 is made no hotter by fire below. Why ? Because 

 the evaporation from the surface carries off just as 

 much heat as the fire infuses from beneath. It is so 

 with a field, when the subsoil is full of water. The 

 water creeps upward to the surface, and is there evap- 

 orated. At the moment of its being changed from a 

 liquid to a vapor, it absorbs heat. This heat it steals 

 away from the soil and the adjoining stratum of air, 

 leaving the surface chill and cold. 



390. If the sun shine upon such a soil, it may infuse 

 a little more heat in the middle of the day than the 

 evaporation carries off; but when the sun declines, 

 the power of evaporation overmasters that of the sun, 

 and the soil again becomes cold. Such lands are often 

 the best in the world after being thoroughly drained, 

 but till drained will produce nothing of much value. 



391. A soil that is finely pulverized, permits the 

 water to pass through it freely, whether upward or 

 downward. The progress is downward after rains, 

 and upward after evaporation. It may be laid down 

 as certain, that the moisture in a cultivated soil is sel- 

 dom stationary. It is always seeking, like the water 

 in a sponge, to equalize itself throughout the mass. 

 If you hold a saturated sponge just below a strong 

 heat, the water in it will rise, and will nearly all 

 escape, in the form of vapor, from the top. So it is 

 with the soil. There falls a heavy rain. The top-soil 



