soon accumulate a large amount of water on those particles
which, being lower and better sheltered from the sun's heat than the
particles of the thin soil, are made cooler.

We have seen that even the most retentive soil,--the stiffest clay,--is made
porous by the repeated passage of water from the surface to the level of
the drains, and that the ability to admit air, which plowing gives it, is
maintained for a much longer time than if it were usually saturated with
water which has no other means of escape than by evaporation at the
surface. The power of dry soils to absorb moisture from the air may be
seen by an examination of the following table of results obtained by
Schuebler, who exposed 1,000 grains of dried soil of the various kinds
named to the action of the air:

Kind of Soil. Amount of Water Absorbed
in 24 Hours.
Common Soil 22 grains.
Loamy Clay 26 grains.
Garden Soil 45 grains.
Brickmakers' Clay 30 grains.

The effect of draining in overcoming drought, by admitting atmospheric
vapor will, of course, be very much increased if the land be thoroughly
loosened by cultivation, and especially if the surface be kept in an open
and mellow condition.

In addition to the moisture received from the air, as above described,
water is, in a porous soil, drawn up from the wetter subsoil below, by the
same attractive force which acts to wet the whole of a sponge of which
only the lower part touches the water;--as a hard, dry, compact sponge will
absorb water much less readily than one which is loose and open, so the
hard clods, into which undrained clay is dried, drink up water much less
freely than they will do after draining shall have made them more friable.

The source of this underground moisture is the "water table,"--the level of
the soil below the influence of the drains,--and this should be so placed
that, while its water will easily rise to a point occupied by the feeding
roots of the crop, it should yield as little as possible for evaporation
at the surface.

Another source of moisture, in summer, is the deposit of dew on the
surface of the ground. The amount of this is very difficult to determine,
and accurate American experiments on the subject are wanting. Of course
the amount of dew is greater here than in England, where Dr. Dalton, a
skillful examiner of atmospheric phenomena, estimates the annual deposit
of dew to equal a depth of five inches, or