270 
On Draining. 
falls from the heavens must first displace an equal volume of air 
before it can enter the soil ; the water would remain on the surface 
and never sink if, by reason of its superior gravity, it did not push 
aside the air in its descent, which it does until it meets with some 
subterranean level where the earth is saturated with the fluid, and 
the rain-water then comes to rest, having disturbed and displaced 
air throughout its whole downward course. And by this action we 
are led to observe one beautiful provision of Nature for renewing 
the constituent air of the soil, and I regard it as an argument in 
favour of deep, as compared with shallow drainage, that a greater 
bulk of earth is thereby filled with air, and with frequently renewed 
air. 
There are other equally beautiful processes incessantly active 
to maintain a full supply, and fresh supplies of air in the soil. 
The continual change of temperature in the soil and in the atmos- 
phere reposing upon it, has its effect ; but probably the most 
potent cause is the unceasing appropriation by plants, or manures, 
or soil, of some one or other of the three gases of which the at- 
mosphere is composed. A renewal of the particular atmospheric 
gas consumed, whether it be oxygen, nitrogen, or carbonic acid, 
must be nearly consentaneous with its use, and is effected by the 
well-known principle of the diffusion of gases, and without which 
neither plants nor animals could live. 
I have spoken of cesspools as useful and convenient breaks in 
lines of drains, particularly in the long run of a main, or where 
several lines of drains converge from two or more directions in one 
common central point to an outfall. The use of the cesspool in 
drainage is an old English practice ; I have found it in several 
counties, both North, South, and Midland : it is usually constructed 
in brick. The specimens now exhibited are made of large earth- 
enware pipes 9 inches in diameter, with a flat tile or foot on which 
to place them in the soil. This plan will be found advantageous 
and cheap, as the foreman drainer may fix his cesspools without 
needing bricks and mortar and a bricklayer. The holes for the 
receiving-pipes are burnt in these cesspools of the proper dimen- 
sions, and the hole for the discharging or outfall-pipe is made 
a little lower than the holes of the receiving-pipes, so that a drip 
or fall from the former takes place, and the run of water from 
each pipe is observable. I have converted these cesspools to 
another use, viz., that of enabling us to introduce water into the 
body of the earth, and apply it to what I have before termed sub- 
irrigation. All the drains of a flat field may be made to issue from 
a c:esspool, into which water from a higher level may be con- 
ducted. A cesspool of the same kind is also to be fixed at the 
outfall end of that field, into which all the drains are conducted. 
Now, by stopping up the outfall-pipe, and letting water into the 
