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THE POPULAR SCIENCE MONTHLY 



with regard to the mortnr of the house. That degree of humidity of 

 the soil is called ground-water y it begins at the lowest limit of the 

 air in the soil. 



It is well known that water becomes solid at a temperature below 

 freezing-point. In becoming ice it changes its consistency totally, 

 but its volume not very much, increasing it by about six per cent., 

 one hundi-ed volumes of water becoming one hundred and six of ice. 

 In a frozen soil there must have been a certain quantity of water. 

 This water in freezing has become a kind of cement for the particles 

 of the soil, and gives it a solidity which the liquid water could not 



Fig. 1. 



impart. Although such frozen soil is as hard to work as stone, we 

 have no right to assume that it is impermeable to air or gases of any 

 kind. 



Those pores of the soil which were free from water cannot be nar- 

 rowed much by the expansion of the neighboring pores through the 



