and its Discharge by Drains. 
155 
a shallower one, Is consistent with the laws of hydraulics, and is 
corroborated by numberless observations on the action of wells, 
&c. ; but the cause of the deeper drain receiving more water in a 
given time is not so obvious. An opposite result, as to time, 
would rather be expected from the fact of water falling on the 
surface having to permeate a greater mass of earth, both perpen- 
dicularly and horizontally, in order to reach the deep drain. A 
natural agricultural bed of porous soil resembles an artificial 
filter, and it is unquestionable that the greater the depth of matter 
composing such filter, the slower is the passage of water through 
it. In stiff loams and clays, however, but more particularly as 
regards the latter earth, the resemblance ceases, as these soils can 
permit free ingress and egress to rain-water, only after the esta- 
blishment of that thorough net-work of cracks or fissures, which 
is occasioned in them by the shrinkage of the mass from the joint 
action of drains and superficial evaporation. These fissures seem 
to stand in the stead of porosity in such soils, and serve to conduct 
water to drains rapidly after it has trickled through the worked 
bed ; it is possible, too, that in deeply drained clays of certain 
texture the fissures may be wider, or more numerous, in conse- 
quence of the contraction of a greater bulk of earth than when 
such soil is drained to a less depth. However this may be, it is 
asserted by several respectable and intelligent farmers m Kent, 
who have laid drains very deeply in clays and stiff soils, that the 
flow from the deepest drains invariably commences and ceases 
sooner than from shallower drains, after rain. On this interest- 
ing and unexplored subject I hope to be able to furnish you with 
multiplied observations after next winter, and trust also to receive 
the co-operation of members of the Society in making them in 
different soils, and with due regard to all those phenomena which 
may influence the results, or be detected by them. 
The consideration of the depth of drains has been too generally 
limited to the mere exigencies of culture and implements, com- 
bined with the natural desire to restrict expense when the mate- 
rials used were dear, and the cost of earth-work great. These 
adventitious circumstances have certainly tended to obscure from 
view the true principles on which drainage should be founded, and 
on which the utmost benefits to be derived from it depend. The 
question of distance between drains is important on the score of 
expense, and it will be wise to err on the right side, and keep 
within safe limits; but insufficiency of depth can only be reme- 
died by a new outlay. So far as experience can illuminate the 
subject, we know that many agriculturists have, a second time, 
drained their fields to a greater depth ; it may, however, be 
doubted whether any one has taken up deep drains, and placed 
them nearer the surface, or nearer together. The system of dqep 
