Farm Duainaof. 365 



which it has no means of discharging except by evaporation, 

 it will, by the time it has discharged it, be 10*^ colder than 

 it wonld have been had it had the power to discharge it by 

 filtration, which is more practically stated thus : If one 

 pound of water to one hundred pounds of earth already 

 filled be added so that it is to be lost by evaporation, it low- 

 ers the temperature 10*. 



Had the same soil the means of ridding itself by drains, 

 no effect is produced beyond what is due to the relative tem^ 

 peratures of the rain and of the soil. It is known by actual 

 trial that four times as much heat is required to evaporate a 

 given quantity of water as is required to raise the same 

 amount from the freezing to the boiling point. 



Another serious disadvantage of water in a soil is seen 

 from the fact that if a soil is filled with water it prevents the 

 access of air, and the soil must necessarily be of the tem- 

 perature of the water it contains, which, if it could be with- 

 drawn by drains, would soon be filled with warm air from 

 above. 



Mr. Josiah Parks, an eminent writer on drainage, says 

 the result of thirty-five observations showed the drained soil, 

 at seven inches in depth, was 10° warmer than the same 

 soil at the same depth undrained. He further says that the 

 undrained soil, at the depth of seven inches, never exceeds 

 4:7'^, while after a thunder shower the drained reached 6Q°y 

 a difference of 19" ; and further, he found at a depth of two 

 and one-half teet it 'was 48'^, considering which, we see 

 what the effects must be in a hot day with the earth's sur- 

 face and the air heated to a great degree, and a shower of 



