On Deep Draining. 491 
by the figures I, 2, 3, then if three drahis be cut 20, 40, and 
60 inches deep, their draught or action on the soil will be indi- 
^ A T] (■ 
cated by the lines A, B, and C. A will drain on the surface a 
greater distance in proportion than B, and B than C ; but B will 
command not only a portion of the subsoil, but also of the sur- 
face in stratum 1 not affected by A, and C will act in a similar 
manner with reference to 2, showing that deep drains must be the 
most effective; but to ensure this etlectiveness the drains should 
be filled with some substance through which water can percolate 
freely throughout their depth. 
In soil which has been broken up by the plough and ridged, 
the rain-water falling upon the surface will, as before described, 
pass through the soil at a level until it reaches the depression of 
the furrow, which, if the land be perfectly level, will become a pool 
or canal of water, as A A (usually called surface, or top water) ; 
if the land be inclined the furrow will become a small stream, 
and by carrying away the water will act as a vent, and partially 
drain the ridge. Under a continuance of rain the level between 
the furrows and the ridge will assume an inclination proportionate 
to the tenacity of the soil, thus ; if B C be the inclination of the 
ridge, and B D the inclination assumed by the water level, the 
space between these two lines will show the amount of soil 
drained by the furrow, E ; thus, when the height of the ridge is 
greater than the summit of the inclination at which the wafer 
level stands, it is erroneously concluded that the land is ed'ectually 
drained; yet wheat which looks well on heavy lands early in the 
spring, will turn yellow in a wet May, the period when the roots 
VOL. VI. 2 L 
