TILE DRAINAGE. 19 



capillaries are full (and its proper air-spaces empty), by sim- 

 ply dipping its lower part in water. Saturate the other by 

 submerging it in a small tin pail of water as nearly the size 

 of the sponge as may be. Put the other sponge in the same 

 sort of tin pail, only perforated like a colander. Hang the 

 two pails (containing the sponges) out in the freezing air. 

 You will find the sponge in the colander pail frozen far soon- 

 er than the other. It would freeze deeper if long and sunk 

 into the ground. Now set both pails on a gridiron or wire 

 support over a stove where the temperature is not over 60 

 or 70, like the spring atmosphere. The aerated sponge in 

 the perforated pail will be thawed long before the other. 

 Air and warmth can circulate through it. It is honey-comb- 

 ed. But warmth gets access to the other sponge only at the 

 bottom, and air only at the top. The ice in an ice-house 

 keeps well if the air is kept out. It melts fast if air gets in 

 and honey-combs it. 



Partly as inferences from or corollaries of the proofs given 

 in our fifth proposition above, follow both our sixth and 

 seventh. 



Sixth. Removing surplus moisture down through the soil 

 by tile drainage lengthens the season of tillage, crop growth, 

 and harvest. It increases it in spring, as already seen, by 

 saving the time and sunheat otherwise simply wasted in 

 thawing and drying a soaked or flooded soil. It increases it 

 after each soaking rain of the crop season by carrying the 

 surplus water quickly downward (with its warmth) through 

 the open air-spaces, leaving the soil ready for plant-growth, 

 and dry enough for tillage far sooner after each shower. It 

 increases the time of growth and harvest, especially of late 

 varieties of potatoes, by keeping the soil dry enough for 

 growth and digging, even after the heavy rains of autumn 

 begin to come. 



Seven th. Tile drainage increases the extent of root pasturage. 

 Roots of most trees (except water-elms, willows, soft maples, 

 and other swamp and lowland trees) and of most agricultu- 



