158 MASSACHUSETTS AGRICULTURE. 



surface. It requires as much heat to evaporate a cubic inch of 

 water, it is said, as would raise the temperature of live and a 

 half inches from the freezing to the boiling point. To evapo- 

 rate the fall of an inch of water from an acre of land demands 

 an amount of solar heat sufficient to raise the temperature of 

 the dry soil of an acre to the depth of ten inches, no less than 

 ninety-nine degrees. Then when the fact is considered that forty 

 or more inches of water fall annually upon every acre of soil, 

 the importance of underdrainage, as a means of keeping up 

 the temperature of the soil, cannot but be observed and 

 acknowledged. Owing to radiation and other agencies, the 

 difference between the temperature of drained and undrained 

 land is not so great as theory would make it. Much of the 

 heat is rendered latent — i. e., not perceptible by a thermometer. 

 The vapor yielded by a cubic inch of water, evaporated under 

 the ordinary atmospheric pressure of fifteen pounds to the 

 square inch, contains sufficient latent heat to raise the tem- 

 perature of nine hundred and ninety cubic inches of water one 

 degree. A wet soil, then, that has no way of freeing itself of 

 an excess of water, but by evaporation, will be cold for the 

 reasons given, and the crop will be both later and inferior to 

 what it would be, provided the soil was freed from this excess 

 of moisture by drainage. Hence, also, the liability to injury 

 from frosts, both late and early, over such undrained regions. 



Soils impregnated with stagnant waters are bad conductors 

 of heat from the sun downwards, and good conductors of cold. 

 Thus is tlie heat absorbed by day, and radiated into space by 

 night. Not so with well drained soils, for such retain it for the 

 promotion of the growth of plants. Acids are developed by 

 cold, wet soils, and other compounds, injurious to the healthful 

 condition of growing crops. The mixing of the latest fall of 

 rain with the stagnant water in the soil, causes a mutual 

 decomposition, injurious to vegetable life, checking the growth 

 and diminishing tlie amount of the crop. These are some 

 of the evils incident upon an excess of water in the soil, which 

 may be removed or cured by underdraining, provided there is 

 sufficient fall. 



By drainage tlie aeration of the soil is greatly promoted. 

 The stagnant water being removed, the pores of the soil are 

 open for the reception of atmospheric air, dew or rain-water. 



