3 
weather. They cake, and present only a small 
surface to the air ; and the vegetation on them 
is generally burnt up as readily as on sands.” 
Liebig and others have shown that rain ge- 
nerally contains substances in the highest de- 
gree useful to plants ; and that soils have the 
power of abstracting these substances from it 
in passing through them. It has been further 
shown by chemists that various injurious sub- 
stances are washed out of the soil where a 
perfect system of drainage is in operation, or 
are so changed in their nature as to become 
innocuous. 
Various experiments have shown that rain 
when percolating through the soil has a strong 
influence in raising the temperature of the 
latter, or equalising it to a greater depth. 
This may be termed a positive cause of in- 
creased temperature ; but there is also a nega- 
tive cause tending to the same end, namely, 
the decrease of evaporation from drained soils. 
By a natural law all bodies when undergoing 
expansion absorb a large amount of heat ; thus, 
when a solid is changed into a fluid, or a fluid 
inro a gas, heat is abstracted from all bodies 
in contact with them. A great amount of 
evaporation is constantly taking place from the 
surface of soil saturated with water, and the 
temperature of the soil is consequently lowered; 
whereas when the amount of moisture does 
not greatly exceed that for which the soil has 
a natural affinity, but little evaporation takes 
place, and that portion of the solar heat which 
would be dissipated in evaporating the water 
is applied to raising the temperature of the soil 
itself. 
The Soil considered in reference to its 'power 
of absorbing and retaining Water. — All porous 
bodies have the power of attracting or absorb- 
ing liquids, in a greater or less degree, by virtue 
of a particular property called capillary attrac- 
tion. Thus if a piece of lump sugar, or a damp 
sponge be placed in contact with water, how- 
ever slightly, the water rapidly goes through 
every part of it. So it is with soils, as every 
one must have noticed in the familiar instance 
of a flower-pot rapidly sucking up water from 
the flat on which it stands. 
Capillary attraction acts more rapidly in 
some soils than in others ; thus, we find that 
inpuro clay it exhibits its influence but slowly; 
in agricultural clays, into the composition of 
which some of the more porous earths enter, 
its action is more rapid ; while gravel, sand, or 
peat speedily absorb as much water as they are 
capable of holding on being brought into con- 
tact with it. 
This power of attraction also manifests itself 
on the surface of bodies, and may be called the 
attraction of adhesion. Soils, in common with 
all other bodies, possess this property, and 
posses* it in a greater or less degree according 
to the aggregate which the particles of a given 
bulk present. Thus clay may, by means of 
kneading be made to contain a very large 
quantity of water. Sand and chalk, the par- 
ticles of which are coarser, exert a less degree 
of adhesive attraction for water. 
It has been found that sand was capable of 
holding 25 per cent., loamy soil 40 per cent., 
N clay loam 50 per cent., and pu r e clay 70 per 
cent., cf their own weights of water when the 
water was merely poured upon them in a dry 
state till it began to drop. 
Clay soils are called impervious soils, because 
in their natural state they resist the passage of 
water through them. They are called reten- 
tive soils, because if water does gain access to 
them, their power of adhesion enables them to 
retain a large quantity of it for a great length 
of time. These properties have a very injuri- 
ous effect on all agricultural operations, and 
their removal is one of the results which the 
scientific drainer seeks to effect. Let us con- 
sider how this i3 to be accomplished. 
We have it in our own power to increase for 
a time the permeability of clay soils, by pul- 
verizing them when dry, thereby separating 
their parts as to afford a ready passage to the 
water. Natural causes also have a like tenden- 
cy. The summer droughts causes numerous 
cracks and fissures, which admit the rains to 
all parts of the soil. This, however, on un- 
drained clay land is found to be an evil ; for 
by means of it the rain is enabled to penetrate 
and saturate the soil to a considerable depth ; 
while their great adhesive power retains it to 
an extent which reduces the soil to the state- of 
a quagmire. 
When clay is properly and thoroughly drain- 
ed a new element is brought into operation by 
the constant supply of air to the soil. By its 
means the permeability is increased, while the 
adhesiveness, if not removed, is at least pre- 
vented from exercising any other than a bene- 
ficial influence. If we pour water on the earth 
in a flower pot, which has become somewhat 
dry, it refuses at first to absorb it. The water 
appears to rest on a plate of silver, which 
opposes its entrance into the soil. This shin- 
ing appearance is caused by the air in the soil. 
After a little time the water sinks in, and 
generally passes through to the stand to be after- 
wards earned up by again capillary attraction. 
The same thing happens on a large scale on 
land which has been drained. The hole in the 
flower pot is represented by the drain, which 
permits the air to penetrate to all parts of the 
drained soil. 
We have seen that soils vary in their power 
of capillary attraction, according as they are 
composed of one substance or anoiher ; but 
the same soila also vary according to the cir- 
cumstances in which they arc placed. The 
universal law of gravitation asserts its power, 
and places a limit on the height to which fluids 
can be raised in porous bodies by capillai’y 
attraction. If we fill a sponge with water, and 
place it on a table, we shall readily discover 
