EFFECTS OF DRAINAGE UPON THE CONDITION OF THE SOIL.
Drainage deepens the Soil, and gives the roots a larger
pasture.--Cobbett's Lucerne 30 feet deep.--Mechi's Parsnips 13 feet
long!--Drainage promotes Pulverization.--Prevents
Surface-Washing.--Lengthens the Season.--Prevents Freezing
out.--Dispenses with Open Ditches.--Saves 25 per cent. of
Labor.--Promotes absorption of Fertilizing Substances from the
Air.--Supplies Air to the Roots.--Drains run before Rain; so do
some Springs.--Drainage warms the Soil.--Corn sprouts at 55 deg.; Rye
on Ice.--Cold from Evaporation.--Heat will not pass downward in
Water.--Count Rumford's Experiments with Hot Water on
Ice.--Aeration of Soil by Drains.
The benefits which high-lands, as we ordinarily call them, in
distinction from swamp or flowed lands, derive from drainage, may be
arranged in two classes, _mechanical_ and _chemical_; though it is not
easy, nor, indeed, is it important, to maintain this distinction in all
points. Among those which partake rather of the nature of mechanical
changes, are the following:
_Drainage deepens the soil._ Every one who has attempted to raise
deep-rooted vegetables upon half-drained swamp-land, has observed the
utter impossibility of inducing them to extend downward their usual
length. Parsnips and carrots, on such land, frequently grow large at the
top, but divide into numerous small fibres just below the surface, and
spread in all directions. No root, except those of aquatic plants, will
grow in stagnant water. If, therefore, it is of any advantage to have a
deep, rather than a shallow soil, it is manifestly necessary, from this
consideration alone, to lower the line of standing water, at least, to
the extent to which the roots of our cultivated crops descend. A deep
soil is better than a shallow one, because it furnishes a more extensive
feeding-ground for the roots. The elements of nutrition, which the plant
finds in the soil, are not all upon the surface. Many of them are washed
down by the rains into the subsoil, and some are found in the
decomposing rocks themselves. These, the plants, by a sort of instinct,
search out and find, as well in the depths of the earth as at its
surface, if no obstacle opposes. By striking deep roots again, the
plants stand more firmly in the earth, so that they are not so readily
drawn out, or shaken by the winds. Indeed, every one knows that a soil
two feet deep is better than one a foot deep; and market-gardeners and
nursery-men show, by their practice, that they know, if others do not,
that a trenched soil three feet deep is better than one of any less
depth. We all know that Indian corn, in a dry soil, sends down its
rootlets two feet or more, as well as most of the grasses. Cobbett says:
"The lucerne will send its roots thirty feet into a dry bottom!" The
Chinese yam, recently introduced, grows downward two or three feet. The
digging of an acre of such a crop, by the way, on New England soil
generally, would require a corps of sappers and miners, especially when
we consider that the yam grows largest end downward. However, the yam
may prove a valuable acquisition to the country. Every inch of
additional soil gives 100 tons of active soil per acre.
Says Mr. Denton:
"I have evidence now before me, that the roots of the wheat plant,
the mangold wurzel, the cabbage, and the white turnip, frequently
descend into the soil to the depth of three feet. I have myself
traced the roots of wheat nine feet deep. I have discovered the
roots of perennial grasses in drains four feet deep; and I may
refer to Mr. Mercer, of Newton, in Lancashire, who has traced the
roots of rye grass running for many feet along a small pipe-drain,
after descending four feet through the soil. Mr. Hetley, of Orton,
assures me that he discovered the roots of the mangolds, in a
recently made drain, five feet deep; and the late Sir John Conroy
had many newly-made drains, four feet deep, stopped by the roots of
the same plants."
Mr. Sheriff Mechi's parsnips, however, distance anything in the way of
deep rooting that has yet been recorded. The Sheriff is a very deep
drainer, and an enthusiast in agriculture, and Nature seems to delight
to humor his tastes, by performing a great many experiments at his
famous place called Tiptree Hall. He stated, at a public meeting, that,
in his neighborhood, where a crop of parsnips was growing on the edge of
a clay pit, the roots were observed to descend 13 feet 6 inches; in
fact, the whole depth to which this pit had once been filled up!
_Drainage assists pulverization._ It was Tull's theory that, by the
comminution, or minute division, of soils alone, without the application
of any manures, their fertility might be permanently maintained; and he
so far supported this theory as, by repeated plowings, to produce twelve
successive crops of wheat on the same land, without manure. The theory
has received support from the known fact, that most soils are benefitted
by Summer fallowing. The experiments instituted for the purpose of
establishing this theory, although they disproved it, showed the great
value of thorough pulverization. It is manifest that a wet soil can
never be pulverized. Plowing clayey, or even loamy soil, when wet, tends
rather to press it together, and render it less pervious to air and
water.
The first effect of under-draining is to dry the surface-soil, to draw
out all the water that will run out of it, so that, in early Spring, or
in Autumn, it may be worked with the plow as advantageously as undrained
lands in mid-Summer.
Striking illustrations of the benefits of thorough pulverization will be
found in the excellent remarks of Dr. Madden, given in a subsequent
chapter.
_Drainage prevents surface-washing._ All land which is not level, and is
not in grass, is liable to great loss by heavy rains in Spring and
Autumn. If the land is already filled with water, or has not sufficient
drainage, the rain cannot pass directly downward, but runs away upon the
surface, carrying with it much of the soil, and washing out of what
remains, of the valuable elements of fertility which have been applied
with such expense. If the land be properly drained, the water falling
from the clouds is at once absorbed, and passes downwards, saturating
the soil in its descent, and carrying the soluble substances with it to
the roots, and the surplus water runs away in the artificial channels
provided by the draining process. So great is the absorbent power of
drained land, that, after a protracted drought, all the water of a heavy
rainstorm will be drunk up and held by the soil, so that, for a day or
two, none will find its way to the drains, nor will it run upon the
surface.
_Drainage lengthens the season for labor and vegetation._ In the colder
latitudes of our country, where a long Winter is succeeded by a torrid
Summer, with very little ceremony by way of an intervening Spring,
farmers have need of all their energy to get their seed seasonably into
the ground. Snow often covers the fields in New England into April; and
the ground is so saturated with water, that the land designed for corn
and potatoes, frequently cannot be plowed till late in May. The manure
is to be hauled from the cellar or yard, over land lifted and softened
by frost, and all the processes of preparing and planting, are
necessarily hurried and imperfect. In the Annual Report of the Secretary
of the Board of Agriculture, of the State of Maine, for 1856, a good
illustration of this idea is given: "Mr. B. F. Nourse, of Orrington,
plowed and planted with corn a piece of his drained and subsoiled land,
in a drizzling rain, after a storm of two days. The corn came up and
grew well; yet this was a clayey loam, formerly as wet as the adjoining
grass-field, upon which oxen and carts could not pass, on the day of
this planting, without cutting through the turf and miring deeply. The
nearest neighbor said, if he had planted that day, it must have been
from a raft." Probably two weeks would be gained in New England, in
Spring, in which to prepare for planting, by thorough-drainage, a gain,
which no one can appreciate but a New England man, who has been obliged
often to plow his land when too wet, to cut it up and overwork his team,
in hauling on his manure over soft ground, and finally to plant as late
as the 6th of June, or leave his manure to waste, and lose the use of
his field till another season; and all because of a surplus of cold
water.
Mr. Yeomans, of New York, in a published statement of his experience in
draining, says, that on his drained lands, "the ground becomes almost as
dry in two or three days after the frost comes out in Spring, or after a
heavy rain, as it would do in as many weeks, before draining." But the
gain of time for labor is not all. We gain time also for vegetation, by
thorough-drainage. Ten days, frequently, in New England, may be the
security of our corn-crop against frost. In less than that time, a whole
field passes from the milky stage, when a slight frost would ruin it, to
the glazed stage, when it is safe from cold; and twice ten days of warm
season are added by this removal of surplus water.
_Drainage prevents freezing out._ Mr. John Johnston, of Seneca County,
New York, in 1851, had already made sixteen miles of tile drains. He had
been experimenting with tiles from 1835, and had, on four acres of his
drained clayey land, raised the largest crop of Indian corn ever
produced in that county--eighty-three bushels of shelled corn to the
acre.
He states, that on this clayey soil, when laid down to grass, "not one
square foot of the clover froze out." Again he says, "Heretofore, many
acres of wheat were lost on the upland by freezing out, and none would
grow on the lowlands. Now there is no loss from that cause."
The growing of Winter wheat has been entirely abandoned in some
localities on account of freezing out, or Winter-killing; and one of the
worst obstacles in the way of getting our lands into grass, and keeping
them so, is this very difficulty of freezing out. The operation seems to
be merely this: The soil is pulverized only to the depth of the plow,
some six or eight inches. Below this is a stratum of clay, nearly
impervious to water. The Autumn rains saturate the surface soil, which
absorbs water like a sponge. The ground is suddenly frozen; the water
contained in it crystallizes into ice; and the soil is thrown up into
spicules, or honey-combs; and the poor clover roots, or wheat plants,
are drawn from their beds, and, by a few repetitions of the process,
left dead on the field in Spring. Draining, followed by subsoiling, lets
down the falling water at once through the soil, leaving the root bed of
the plants so free from moisture, that the earth is not "heaved," as the
term is, and the plants retain their natural position, and awaken
refreshed in the Spring by their Winter's repose.
_There are no open ditches on under-drained land._ An open ditch in a
tillage or mowing-field, is an abomination. It compels us, in plowing,
to stop, perhaps midway in our field; to make short lands; to leave
headlands inconvenient to cultivate; and so to waste our time and
strength in turning the team, and treading up the ground, instead of
profitably employing it in drawing a long and handsome furrow the whole
length of the field, as we might do were there no ditch. Open ditches,
as usually made, obstruct the movement of our teams as much as fences,
and a farm cut into squares by ditches, is nearly as objectionable as a
farm fenced off into half or quarter-acre fields.
In haying, we have the same inconvenience. We must turn the
mowing-machine and horse-rake at the ditch, and finish by hand-labor,
the work on its banks; we must construct bridges at frequent intervals,
and then go out of our way to cross them with loads, cutting up the
smooth fields with wheels and the feet of animals. Or, what is a
familiar scene, when a shower is coming up, and the load is ready,
Patrick concludes to drive straight to the barn, across the ditch, and
gets his team mired, upsets his load, and perhaps breaks the leg of an
animal, besides swearing more than half a mile of hard ditching will
expiate. Such accidents are a great temptation to profanity, and
under-draining might properly be reckoned a moral agent, to counteract
such traps and pitfalls of the great adversary.
A moment's thought will satisfy any farmer who has the means, that true
economy dictates a liberal expenditure of labor, at once, to obviate
these difficulties, rather than be subject for a lifetime to the
constant petty annoyances which have been named.
Open ditches, even when formed so skillfully that they may be
conveniently crossed, or water-furrows which remain where land is laid
into ridges by back-furrowing, as much of our flat land must be, if not
under-drained, are serious obstructions, at the best.
They render the soil unequal in depth, taking it from one point where it
is wanted, and heaping it upon another where it is not wanted, thus
giving the crops an uneven growth. They render the soil also unequal in
respect to moisture, because the back or top of the ridge must always be
drier than the furrow.
Thorough-drained land may be laid perfectly flat, giving us, thus, the
control of the whole field, to divide and cultivate according to
convenience, and making it of uniform texture and temperature.
Attempts have been made, to estimate the saving in the number of horses
and men by drainage, and it is thought to be a reasonable calculation to
fix it at one in four, or twenty-five per cent. It probably will strike
any farmer as a fair estimate, that, on land which needs drainage, it
will require four horses and four men to perform the same amount of
cultivation, that three men and three horses may perform on the same
land well drained.
_Drained land will not require re-planting._ There is hardly a farmer in
New England, who does not, each Spring, find himself compelled to
re-plant some portion of his crop. He is obliged to hurry his seed into
the ground, at the earliest day, because our season for planting is
short at the best. If, after this, a long cold storm comes, on wet land,
the seed rots in the ground, and he must plant again, often too late,
incurring thus the loss of the seed, the labor of twice doing the same
work, the interruption of his regular plan of business, and often the
partial failure of his crop.
Upon thorough-drained land, this cost and labor could rarely be
experienced, because nothing short of a small deluge could saturate well
drained land, so as to cause the seed to fail, if sowed or planted with
ordinary care and prudence, as to the season.
_Drained land is lighter to work._ It is often difficult to find a day
in the year, when a wet piece of land is in suitable condition to plow.
Usually, such tracts are unequal, some parts being much wetter than
others, because the water settles into the low places. In such fields,
we now drive our team knee deep into soft mud, and find a stream of
water following us in the furrow, and now we rise upon a knoll, baked
hard, and sun-cracked; and one half the surface when finished is shining
with the plastered mud, ready to dry into the consistency of bricks,
while the other is already in hard dry lumps, like paving stones, and
about as easily pulverized.
This is hard work for the team and men, hard in the plowing, and hard
through the whole rotation. The same field, well drained, is friable and
porous, and uniform in texture. It may be well plowed and readily
pulverized, if taken in hand at any reasonable season.
Land which has been puddled by the tread of cattle, or by wheels,
acquires a peculiar consistency, and a singular capacity to hold water.
Certain clays are wet and beaten up into this consistency, to form the
bottoms of ponds, and to tighten dams and reservoirs. A soil thus
puddled, requires careful treatment to again render it permeable to
water, and fit for cultivation. This puddling process is constantly
going on, under the feet of cattle, under the plow and the cart-wheels,
wherever land containing clay is worked upon in a wet state. Thus, by
performing a day's work on wet land, we often render necessary as much
additional labor as we perform, to cure the evil we have done.
_We may haul loads without injury on drained land._ On many farms, it is
difficult to select a season for hauling out manure, or carting stones
from place to place, when great injury is not done to some part of the
land by the operation. Many farmers haul out their manure in Winter, to
avoid cutting up their farms; admitting that the manure is wasted
somewhat by the exposure, but, on the whole, choosing this loss as the
lesser evil. In spreading manure in Spring, we are often obliged to
carry half loads, because the land is soft, not only to spare our
beasts, but also to spare our land the injury by treading it. Drained
land is comparatively solid, especially in Spring, and will bear up
heavy loads with little injury.
_Drained land is least injured by cattle in feeding._ Whether it is good
husbandry to feed our mowing fields at any time, is a question upon
which farmers have a right to differ. Without discussing the question,
it is enough for our purpose, that most farmers feed their fields late
in the Autumn. Whether we approve it, or not, when the pastures are bare
and burnt up, and the second crop in the home-field is so rich and
tempting, and the women are complaining that the cows give no milk, we
usually bow to the necessity of the time, and "turn in" the cows. The
great injury of "Fall-feeding" is not usually so much the loss of the
grass-covering from the field, as the poaching of the soil and
destruction of the roots by treading. A hard upland field is much less
injured by feeding, than a low meadow, and the latter less in a dry than
a wet season. By drainage, the surplus water is taken from the field.
None can stand upon its surface for a day after the rain ceases. The
soil is compact, and the hoofs of cattle make little impression upon it,
and the second or third crop may be fed off, with comparatively little
damage.
_Weeds are easily destroyed on drained land._ If a weed be dug or pulled
up from land that is wet and sticky, it is likely to strike root and
grow again, because earth adheres to its roots; whereas, a stroke of the
hoe entirely separates the weeds in friable soil from the earth, and
they die at once. Every farmer knows the different effect of hoeing, or
of cultivating with the horse-hoe or harrow, in a rain storm and in dry
weather. In one case, the weeds are rather refreshed by the stirring,
and, in the other, they are destroyed. The difference between the
surface of drained land and water-soaked land is much the same as that
between land in dry weather under good cultivation, and land just
saturated by rain.
Again, there are many noxious weeds, such as wild grasses, which thrive
only on wet land, and which are difficult to exterminate, and which
give us no trouble after the land is lightened and sweetened by
drainage. Among the effects of drainage, mainly of a chemical nature, on
the soil, are the following:
_Drainage promotes absorption of fertilizing substances from the air._
The atmosphere bears upon its bosom, not only the oxygen essential to
the vitality of plants, not only water in the form of vapor, to quench
their thirst in Summer droughts, but also various substances, which rise
in exhalations from the sea, from decomposing animals and vegetables,
from the breathing of all living creatures, from combustion, and a
thousand other causes. These would be sufficient to corrupt the very
air, and render it unfit for respiration, did not Nature, with her
wondrous laws of compensation, provide for its purification. It has
already been stated, how the atmosphere returns to the hills, in clouds
and vapor, condensed at last to rain, all the water which the rivers
carry to the sea; and how the well-drained soil derives moisture, in
severest time of need, from its contact with the vapor-loaded air. But
the rain and dew return not their waters to the earth without treasures
of fertility. Ammonia, which is one of the most valuable substances
found in farm-yard manures, and which is a constant result of
decomposition, is absorbed in almost incredible quantities by water.
About 780 times its own bulk of ammonia is readily absorbed by water at
the common temperature and pressure of the atmosphere; and, freighted
thus with treasures for the fields, the moisture of the atmosphere
descends upon the earth. The rain cleanses the air of its impurities,
and conveys them to the plants. The vapors of the marshes, and of the
exposed manure heaps of the thriftless farmer, are gently wafted to the
well-drained fields of his neighbor, and there, amidst the roots of the
well-tilled crops, deposit, at the same time, their moisture and
fertilizing wealth.
Of the wonderful power of the soil to absorb moisture, both from the
heavens above and the earth beneath--by the deposition of dew, as well
as by attraction--we shall treat more fully in another chapter. It will
be found to be intimately connected with the present topic.
_Thorough drainage supplies air to the roots._ Plants, if they do not
breathe like animals, require for their life almost the same constant
supply of air. "All plants," says Liebig, "die in soils and water
destitute of oxygen; absence of air acts exactly in the same manner as
an excess of carbonic acid. Stagnant water on a marshy soil excludes
air, but a renewal of water has the same effect as a renewal of air,
because water contains it in solution. When the water is withdrawn from
a marsh, free access is given to the air, and the marsh is changed into
a fruitful meadow." Animal and vegetable matter do not decay, or
decompose, so as to furnish food for plants, unless freely supplied with
oxygen, which they must obtain from air. A slight quantity of air,
however, is sufficient for putrefaction, which is a powerful deoxydizing
process that extracts oxygen even from the roots of plants.
We are accustomed to think of the earth as a compact body of matter,
vast and inert; subject, indeed, to be upheaved and rent by volcanoes
and earthquakes, but as quite insensible to slight influences which
operate upon living beings and upon vegetation. This, however, is a
great mistake; and it may be interesting to refer to one or two facts,
which illustrate the wonderful effect of changes of the atmosphere upon
the soil, and upon the subterranean currents of the earth. The following
is from remarks by Mr. Denton, in a public address:
"But, as a proof of the sensibility of a soil drained four feet
deep, to atmospheric changes, I may mention, that my attention has
been, on more than one occasion, called to the circumstance that
drains have been observed to run, after a discontinuance of that
duty, without any fall of rain on the surface of the drained land;
and, upon reference to the barometer, it has been found that the
quicksilver has fallen whenever this has occurred. Mr. George
Beaumont, jun., who first afforded tangible evidence of this
extraordinary circumstance, has permitted me to read the following
extracts of his letter:
"'I can verify the case of the drains running without rain, during
a falling barometer, beyond all doubt.
"'The case I named to you last year of the barometer falling four
days consecutively, and with rapidity, was a peculiarly favorable
time for noticing it, as it occurred in a dry time, and the drains
could be seen distinctly. My man, on being questioned and cautioned
by me not to exaggerate, has declared the actual stream of water
issuing from one particular drain to be as thick as a
three-eighth-inch wire. All the drains ran--they did more than
drop--and ditches, which were previously dry, became quite wet,
with a perceptible stream of water; this gradually ceased with the
change in the density of the atmosphere, as shown by the barometer.
"'During last harvest, 1855, the men were cutting wheat, and on
getting near to a drain outlet, the ditch from the outlet downwards
was observed to be wet, and the drain was dripping. No rain fell in
sufficient quantity to enter the ground. The men drank of the water
while they were cutting the wheat. A few days after, it was dry
again. I have seen and noticed this phenomenon myself.'
"A correspondent of the _Agricultural Gazette_ has stated, that
Professor Brocklesby, of Hartford, in America, had observed the
same phenomena, in the case of two springs in that country; and
explained, that the cause was 'the diminished atmospheric pressure
which exists before a rain.'"
Dr. Lardner states many facts which support the ideas above suggested.
In his lectures on science, he says: "When storms are breaking in the
heavens, and sometimes long before their commencement, and when their
approach has not yet been manifested by any appearances in the
firmament, phenomena are observed, apparently sympathetic, proceeding
from the deep recesses of the earth, and exhibited under very various
forms at its surface." Dr. Lardner cites many instances of fountains
which, when a storm is approaching, burst forth with a violent flow of
water, before any rain has fallen.
The cases named by Prof. Brocklesby, referred to by Mr. Denton, are
those of a spring in Rutland, Vermont, and a brook in Concord,
Massachusetts. Prof. Brocklesby states, as the result of his personal
observation, that the spring referred to, supplies an aqueduct; that, in
several instances, when the spring had become so low, in a time of
drought, that no water ran in the aqueduct, it suddenly rose so as to
fill the pipes, and furnish a supply of water, before any rain had
fallen in the neighborhood. This occurrence, he says, was familiar to
the occupants of the premises, and they expected rain in a few days
after this mysterious flow of water; which expectations were usually, if
not always, realized.
The other instance is that of a brook in Concord, Mass., called Dodge's
brook, which Prof. B. says, he was informed, commenced frequently to
rise very perceptibly before a drop of rain had fallen.
We have inquired of our friends in Concord about this matter, and find
that this opinion is entertained by many of the people who live near
this brook, and it is probably well founded, though we cannot ascertain
that accurate observations have been made, so as to afford any definite
results.
_Thorough drainage warms the soil._ It has been stated, on high
authority, that drainage raises the temperature of the soil, often as
much as 15 deg. F. Indian corn vegetates at about 55 deg.. At 45 deg., the seed
would rot in the ground, without vegetating. The writer, however, has
seen rye sprouted upon ice in an ice-house, with roots two inches long,
so grown to the ice that they could only be separated by thawing. Winter
rye, no doubt, makes considerable growth under snow. Cultivated plants,
in general, however, do not grow at all, unless the soil be raised above
45 deg.. The sun has great power to warm dry soils, and, it is said, will
often raise their temperature to 90 deg. or 100 deg., when the air in the shade
is only 60 deg. or 70 deg.. But the sun has no such power to warm a wet soil,
and for several reasons, which are as follows:
1. _The soil is rendered cold by evaporation._ If water cannot pass
through the land by drainage, either natural or artificial, it must
escape, if at all, at the surface, by evaporation. Now, it is a fact
well known, that the heat disappears, or becomes latent, by the
conversion of water into vapor. Every child knows this, practically, at
least, who, in Winter, has washed his hands and gone out without drying
them. The same evaporation which thus affects the hands, renders the
land cold, when filled with water, every gallon of which thus carried
off requires, and actually carries off, as much heat as would raise five
and a half gallons of water from the freezing to the boiling point.
Morton, in his "Encyclopaedia of Agriculture," estimates that it would
require an expenditure of nearly 1,200 pounds of coal per day, to
evaporate artificially one half the rain which falls on an acre during
the year. In other words, about 219 tons of coals annually, would be
required for every acre of undrained land, so as to allow the free use
of the sun's rays for the legitimate purpose of growing and maturing the
crops cultivated upon it. It will not then be surprising that undrained
soils are, in the language of the farmer, "cold."
2. _Heat will not pass downward in water._ If, therefore, your soil be
saturated with water, the heat of the sun, in Spring, cannot warm it,
and your plowing and planting must be late, and your crop a failure.
Count Rumford tried many experiments to illustrate the mode of the
propagation of heat in fluids, and his conclusion, it is presumed, is
now held to be the true theory, that heat is transmitted in water only
by the motion of the particles of water; so that, if you could stop the
heated particles from rising, water could not be warmed except where it
touches the vessel containing it. Heat applied to the bottom of a vessel
of water warms the particles in contact with the vessel, and colder
particles descend, and so the whole is warmed.
Heat, applied to the surface of the water, can never warm it, except so
far as it is conducted downward by some other medium than the water
itself. Count Rumford confined cakes of ice in the bottom of glass jars,
and, covering it with one thickness of paper, poured boiling-hot water
on the top of it, and there it remained for hours without melting the
ice. The paper was placed over the ice, so that the hot water could not
be poured on it, which would have thawed it at once. Every man who has
poured hot water into a frozen pump, hoping to thaw out the ice by this
means, has arrived at the fact, if not at the theory, that ice will not
melt by hot water on the top of it. If, however, a piece of lead pipe be
placed in the pump, resting on the ice, and hot water be poured through
it, the ice will melt at once. In the first instance, the hot water in
contact with the ice becomes cold; and there it remains, because cold
water is heavier than warm, and there it will remain, though the top be
boiling. But when hot water is poured through the pipe, the downward
current drives away the cold water, and brings heated particles in
succession to the ice.
Heat is propagated in water, then, only by circulation; that is, by the
upward movement of the heated particles, and the downward movement of
the colder ones to take their place. Anything which obstructs
circulation, prevents the passage of heat. Chocolate retains heat longer
than tea, because it is thicker, and the hot particles cannot so readily
rise to be cooled at the surface. Count Rumford illustrated this fact
satisfactorily, by putting eider-down into water, which was found to
obstruct the circulation, and to prevent the rapid heating and cooling
of it. The same is true of all viscous substances, as starch and glue;
and so of oil. They retain heat much longer than water or spirits.
In a soil saturated with water, or even in water thickened with mud,
there could then be but little circulation of the particles, even were
the heat applied at the bottom instead of the top. Probably the soil,
though saturated with water, does, to some extent, transmit heat from
one particle of earth to another, but it must be but very slowly.
In the chapter upon Temperature as affected by Drainage, farther
illustrations of this point may be found.
AERATION BY DRAINS.
Among the advantages of thorough-drainage, is reckoned by all, the
circulation of air through the soil. No drop of water can run from the
soil into a drain without its place being supplied by air, unless there
is more water to supply it; so that drainage, in this way, manifestly
promotes the permeation of air through the soil.
But it is claimed that drains may be made to promote circulation of air
in another way, and in dry times, when no water is flowing through them,
by connecting them together by means of a header at the upper ends, and
leaving an opening so that the air may pass freely through the whole
system. Our friend, Prof. Mapes, is an advocate for this practice, and
certainly the theory seems well supported. It is said that in dry, hot
weather, when the air is most highly charged with moisture, currents
thus passing constantly through the earth, must, by contact with the
cooler subsoil, part with large quantities of moisture, and tend to
moisten the soil from the drains to the surface, giving off also with
the moisture whatever of fertilizing elements the air may bear with it.
This point has not escaped the notice of English drainers. Mr. J. H.
Charnock, an assistant commissioner under the Drainage act, in 1843,
read a paper in favor of this practice, but in 1849 he published a
second article in which he suggests doubts of the advantages of such
arrangements, and says he has discontinued their application. He says
they add to the cost of the work, and tend to the decay of the pipes,
and to promote the growth into the pipes, of any roots that may approach
them.
Mr. Parkes, in a published article in 1846, speaks of this idea, but
passes it by as of very little importance. Mr. Denton quotes the
authority of some of his correspondents strongly in favor of this
theory. After trying some experiments himself upon clay soil, he admits
the advantages of such an arrangement for such soil, in the following
not very enthusiastic terms:
"It will be readily understood that as clay will always contract rapidly
under the influence of a draught of air, in consequence of the rapid
evaporation of moisture from its surface, one of the benefits of
draining is thus very cheaply acquired; and for the denser clays it may
possibly be a desirable thing to do, but in the porous soils it would
appear that no advantage is gained by it."
Yet, notwithstanding this summary disposition of the question in
England, it is by no means clear, that in the tropical heat of American
summers, when the difference between the temperature of the air and the
subsoil is so much greater than it can ever be in England, and when we
suffer from severer droughts than are common there, we may not find
substantial practical advantage from the passage of these air currents
through the soil.
We are not aware of experiments in America, accurate enough to be quoted
as authority on the subject.