364 State Boaud ok Agriculture, &c. 



that takes place in a hot summer day when the mercury indicates 

 85 or 90*^, and all nature seems parched. Let there come a 

 shower, and the water falling be evaporated, and who has 

 not noticed the change in temperature. 



Dr. Madden found that the soil of a drained field, in 

 which most of the water was removed from below, was 6^*^ 

 warmer than a similar soil undrained, from which the water 

 was removed by evaporation. The diiference of 6^° is 

 equivalent to an altitude of two thousand feet. 



Writers estimate that during the summer months three 

 inches of water per month are evaporated from wet soils. 

 Three inches of water over the area of an acre would weigh 

 two hundred and seventy-five tons. The amount of heat 

 required to evaporate this must be very great, all of which 

 comes from the air and earth, which becomes reduced in a 

 similar ratio, which accounts for the old expression, " cold, 

 wet land." The more completely we withdraw this water 

 from the surface by drains, the less is the temperature of the 

 soil reduced by the process of evaporation. To illustrate 

 the deleterious efiects of evaporation, let me take as an 

 example a rain fall of one inch on an acre, one hundred 

 tons, which would require all the heat contained in ten tons of 

 coal, a large share of which is absorbed from the earth, con- 

 sequently lowering the temperature of the soil, which has a 

 backward tendency to both the germination of seeds and 

 ripening of crops. Gisborn saj^s the evaporation of one 

 pound of water lowers the temperature of one hundred 

 pounds of soil 10*^ ; that is to say, if to one hundred pounds 

 of soil, holding all the water it can by attraction, but con- 

 taining no water of drainage, is added one pound of water 



