ls in
which the manure is very rapidly exhausted, and it is more than probable
that this effect is due to deficient absorptive power, which leaves the
soluble matters at the mercy of the weather, and liable at any moment
to be washed out by a heavy fall of rain.

The more strictly mechanical properties of the soil, such as its
relations to heat and moisture, are not less important than its chemical
composition. It is known that soils differ so greatly in these respects
as sometimes materially to affect their productive capacity. Thus, for
instance, two soils may be identical in composition, but one may be
highly hygrometric, that is, may absorb moisture readily from the air,
while the other may be very deficient in that property. Under ordinary
circumstances no difference will be apparent in their produce, but in a
dry season the crop upon the former may be in a flourishing condition,
while that on the latter is languishing and enfeebled, merely from its
inability to absorb from the air, and supply to the plant the quantity
of water required for its growth. In the same way, a soil which absorbs
much heat from the sun's rays surpasses another which has not that
property; and though in many cases this effect is comparatively
unimportant, in others it may make the difference between successful and
unsuccessful cultivation in soils which lie in an unfavourable climate
or exposure.

The investigation of the physical characters of soils has attracted
little attention, and we owe all our present knowledge of the subject to
a very elaborate series of researches on this subject, published by
Schuebler, nearly thirty years ago. He determined _1st_, The specific
gravity of the soils; _2d_, The quantity of water which they are capable
of imbibing; _3d_, The rapidity with which they give off by evaporation
the water they have imbibed; that is, their tendency to become dry;
_4th_, The extent to which they shrink in drying; _5th_, Their
hygrometric power; _6th_, The extent to which they are heated by the
sun's rays; _7th_, The rapidity with which a heated soil cools down,
which indicates its power of _retaining_ heat; _8th_, Their tenacity, or
the resistance they offer to the passage of agricultural implements;
_9th_, Their power of absorbing oxygen from the air. Each of these
experiments was performed on several different soils, and on their
mechanical constituents. Schuebler's experiments are undoubtedly
important, and though the