578 
Abstract Report of Agricultural Discussions. 
the floods ; on tlie contrary if free soils are properly drained — witli 
no more drains than are necessary, as has been explained — their 
surfaces instead of being saturated are in an absorbent condition, and 
capable of taking in and storing the rain that falls upon it. This 
they will gradually discharge by the few appropriate drains adopted ; 
and by such means floods may be reduced, instead of being increased, 
as is the case by the too generally adopted treatment of frequent 
parallel drainage. It has been stated that drainage does not diminish 
evaporation ; but reflection and the observation of facts must dispel 
such a notion. It is undeniable that the water discharged from the 
drains must be removed from the action of evaporation on the surface 
of the land : and inasmuch as the drains commence to run, and only 
can run continuously, when the water level in the ground has risen to 
the height of the drains, it is clear that those drains are always 
arresting, in scm.e degi'ce, the iipward action of the water toward the 
surface of the land fi'om which it would be evaporated. Numerous 
experiments clearly demonstrate that directly the water on the soil 
rises to the level of the drains, the drains begin to discharge, and that 
were it not for those drains, the water which finds vent at the drains 
would gradually rise to the surface, and from thence pass ofl" as vapour 
into the air. This fact, while it goes far to show that evaporation 
from free soils must be diminished by the drainage, at once disproves 
the statement, so often repeated, that the extent or period of drought 
is increased. These latter remarks apply merely to free soils. 
We know that the drains in clay soils do not discharge until the 
body of soil from drain to surface has in its grasp sufficient water to 
fill it to the extent of its retentive powers ; and it can be well under- 
stood that evaporation, fed by capillary attraction, will be as great as 
before, so long as the soil is in that state of repletion, although the 
land be drained. In free soils there is no retentive quality to 
maintain, nor is capillary attraction sufficiently active after drainage 
to raise the water from the level of the drains and uphold it at the 
surface of the ground.* Thus we see that not only in the action of 
water through the land, but in the hygrometric influence of the 
atmcsphere, the two descriptions of soils are dificrcntly afiectcd, and 
it becomes manifest that to apply the same princiijles of drainage to 
both is a compoimd fallacy ; a fallacy qua under-di'ainage in its efiect 
upon land-owners individual^, and a fallacy qua arterial drainage in 
the effect upon the water economy of the country generally. 
It is net long since I had the pleasure of reading a paper before 
the Institution of Civil Engineers, having the same object as the 
* TliC amount of evaporation from a constantly saturated surface, like some of 
our stajinant valleys or jient-up l)(!g.s, has never been ascei tained ; but some inter- 
esting" expeiinients were made by ibe late Mr. Cbarnock of Ferrybridge, and 
printed in tbe Society's Journal (vol. x. p. SKi). They were confined, however, 
to the limited surface of a gauge filled with soil, and showed that whereas the 
evaporation from a consfantly-saturatid surface, maintained in that condition, was 
8 in. more than tbe rainfall, that from a drained soil was .5 in. less than the 
rainfall. These experiments are not suttieieutly confirmed to be taken as a guide 
for the evaporation from a natural surface. 
