334 
Agricultural Meteorology . 
the downfall of any heav)' winter's rain ougfht (o have all been 
filtered through the soil and carried off by the drains within 
twenty-four hours after the rain has ceased to fall. It will not be 
surprisintj then, under such circumstances, as the beds of our 
rivers will be called upon to do double duty at no distant time, 
to find that in some parts of the country bridges have to be re- 
built, water-ways widened, and that artificial defences against 
the rapidity of the current or the encroachments on the banks 
have to be strengthened. The spread of inundations, which may 
also be anticipated in our great river-basins, is an evil not so 
easily dealt with, as there are no means of adequately raising the 
soil above the level of the waters. This indeed appears the only 
drawback, and it is a serious one, as it affects many places, towns, 
and residences, which even now are subject to periodical floods, 
some of them very formidable ; there is then a temptation to em- 
bank, but this is only a temporary remedy : since by confining the 
river waters to the immediate vicinity of the cliannel they usually 
occupy, the adjacent lands lose the advantage of that deposit which 
would at last by degrees raise their level ; while that of the river 
itself is, by the alluvial matter brought down by the current, gra- 
dually but surely elevated above the level of the surrounding 
country, as may be seen throughout the north of Italy. M. 
Gasparin is not satisfied that the stripping of the mountain sides 
of their forests will account sufficiently lor the lessened quantity 
of water in the rivers of Europe. He thinks that the influence 
of cultivation, by rendering the earth more porous and absorbent, 
may have a large share in causing it; but thai, on the whole, 
'• their annual volumes depend on certain unknown periods, 
which periods cause certain winds more or less rainy to alternate 
with others; a distant future, when a long series of observations 
shall have been made, will alone permit us to see whether there 
is any regularity in the return of these periods.'' 
As to their effect on vegetation, " The earth ought to have not 
loss than \ of an inch* of water within 1 foott of ihe surface in 
the summer, and never more than ^- within the same dis- 
tance in winter. J; In order to ascertain the depth to which rain 
penetrates, M. Gasparin instituted some experiments, from which 
he concludes that through a perfectly dry argillo-calcareous soil, 
in a state of fallow, rain descends in one day six times the depth 
of the quantity fallen. Thus, a fall of of an inch will sink in 
a day through nearly 2^ inches of the particular soil in the con- 
dition which he described. 
It is only by very slow absorption that it can insensibly furnish 
« In strictness, O'lO = -3937 of an incli, 
+ 30 Cent. = ll-8i. $ 0 • 23 = • 9055 inch. 
