RAIN, EVAPORATION, AND FILTRATION.
Fertilizing Substances in Rain Water.--Amount of Rain Fall in
United States--in England.--Tables of Rain Fall.--Number of Rainy
Days, and Quantity of Rain each Month.--Snow, how Computed as
Water.--Proportion of Rain Evaporated.--What Quantity of Water Dry
Soil will Hold.--Dew Point.--How Evaporation Cools
Bodies.--Artificial Heat Underground.--Tables of Filtration and
Evaporation.
Although we usually regard drainage as a means of rendering land
sufficiently dry for cultivation, that is by no means a comprehensive
view of the objects of the operation.
Rain is the principal source of moisture, and a surplus of moisture is
the evil against which we contend in draining. But rain is also a
principal source of fertility, not only because it affords the necessary
moisture to dissolve the elements of fertility already in the soil, but
also because it contains in itself, or brings with it from the
atmosphere, valuable fertilizing substances. In a learned article by Mr.
Caird, in the Cyclopedia of Agriculture, on the Rotation of Crops, he
says:
"The surprising effects of a fallow, even when unaided by any
manure, has received some explanation by the recent discovery of
Mr. Barral, that rain-water contains within itself, and conveys
into the soil, fertilizing substances of the utmost importance,
equivalent, in a fall of rain of 24 inches per annum, to the
quantity of ammonia contained in 2 cwt. of Peruvian guano, with 150
lbs. of nitrogeneous matter besides, all suited to the nutrition of
our crops."
About 42 inches of rain may be taken as a fair general average of the
rain-fall in the United States. If this supplies as much ammonia to the
soil as 3 cwt. of Peruvian guano to the acre, which is considered a
liberal manuring, and which is valuable principally for its ammonia, we
at once see the importance of retaining the rain-water long enough upon
our fields, at least, to rob it of its treasures. But rain-water has a
farther value than has yet been suggested:
"Rain-water always contains in solution, air, carbonic acid, and
ammonia. The two first ingredients are among the most powerful
disintegrators of a soil. The oxygen of the air, and the carbonic
acid being both in a highly condensed form, by being dissolved,
possess very powerful affinities for the ingredients of the soil.
The oxygen attacks and oxydizes the iron; the carbonic acid seizing
the lime and potash and other alkaline ingredients of the soil,
produces a further disintegration, and renders available the
locked-up ingredients of this magazine of nutriment. Before these
can be used by plants, they must be rendered soluble; and this is
only affected by the free and renewed access of rain and air. The
ready passage of both of these, therefore, enables the soil to
yield up its concealed nutriment."
We see, then, that the rains of heaven bring us not only water, but food
for our plants, and that, while we would remove by proper drainage the
surplus moisture, we should take care to first conduct it through the
soil far enough to fulfill its mission of fertility. We cannot suppose
that all rain-water brings to our fields precisely the same proportion
of the elements of fertility, because the foreign properties with which
it is charged, must continually vary with the condition of the
atmosphere through which it falls, whether it be the thick and murky
cloud which overhangs the coal-burning city, or the transparent ether of
the mountain tops. We may see, too, by the tables, that the quantity of
rain that falls, varies much, not only with the varying seasons of the
year, and with the different seasons of different years, but with the
distance from the equator, the diversity of mountain and river, and
lake and wood, and especially with locality as to the ocean. Yet the
average results of nature's operations through a series of years, are
startlingly constant and uniform, and we may deduce from tables of
rain-falls, as from bills of mortality and tables of longevity,
conclusions almost as reliable as from mathematical premises.
The quantity of rain is generally increased by the locality of mountain
ranges. "Thus, at the Edinburgh Water Company's works, on the Pentland
Hills, there fell in 1849, nearly twice as much rain as at Edinburgh,
although the distance between the two places is only seven miles."
Although a much greater quantity of rain falls in mountainous districts
(within certain limits of elevation) than in the plains, yet a greater
quantity of rain falls at the surface of the ground than at an elevation
of a few hundred feet. Thus, from experiments which were carefully made
at York, it was ascertained that there fell eight and a half inches more
rain at the surface of the ground, in the course of twelve months, than
at the top of the Minster, which is 212 feet high. Similar results have
been obtained in many other places.
Some observations upon this point may also be found in the Report of the
Smithsonian Institution for 1855, at p. 210, given by Professor C. W.
Morris, of New York.
Again, the evaporation from the surface of water being much greater than
from the land, clouds that are wafted by the winds from the sea to the
land, condense their vapor upon the colder hills and mountain sides, and
yield rain, so that high lands near the sea or other large bodies of
water, from which the winds generally blow, have a greater proportion of
rainy days and a greater fall of rain than lands more remote from water.
The annual rain-fall in the lake districts in Cumberland County, in
England, sometimes amounts to more than 150 inches.
With a desire to contribute as much as possible to the stock of accurate
knowledge on this subject, we availed ourselves of the kindly offered
services of our friends, Shedd and Edson, in preparing a carefully
considered article upon a part of our general subject, which has much
engaged their attention. Neither the article itself, nor the
observations of Dr. Hobbs, which form a part of its basis, has ever
before been published, and we believe our pages cannot be better
occupied than by giving them in the language of our friends:
"All vegetables, in the various stages of growth, require warmth, air,
and moisture, to support life and health.
Below the surface of the ground there is a body of stagnant water,
sometimes at a great depth, but in retentive soils usually within a foot
or two of the surface. This stagnant water not only excludes the air,
but renders the soil much colder, and, being in itself of no benefit,
without warmth and air, its removal to a greater depth is very
desirable.
A knowledge of the depth to which this water-table should be removed,
and of the means of removing it, constitutes the science of draining,
and in its discussion, a knowledge of the rain-fall, humidity of the
atmosphere, and amount of evaporation, is very important.
The amount of rain-fall, as shown by the hyetal, or rain-chart, of North
America, by Lorin Blodget, is thirty inches vertical depth in the basin
of the great lakes; thirty-two inches on Lake Erie and Lake Champlain;
thirty-six inches in the valley of the Hudson, on the head waters of the
Ohio, through the middle portions of Pennsylvania and Virginia, and
western portion of North Carolina; forty inches in the extreme eastern
and the northern portion of Maine, northern portions of New Hampshire
and Vermont, south-eastern counties of Massachusetts, Central New York,
north-east portion of Pennsylvania, south-east portion of New Jersey and
Delaware; also, on a narrow belt running down from the western portion
of Maryland, through Virginia and North Carolina, to the north-western
portion of South Carolina; thence, up through the western portion of
Virginia, north-east portion of Ohio, Northern Indiana and Illinois, to
Prairie du Chien; forty-two inches on the east coast of Maine, Eastern
Massachusetts, Rhode Island, and Connecticut, and middle portion of
Maryland; thence, on a narrow belt to South Carolina; thence, up through
Eastern Tennessee, through Central Ohio, Indiana, and Illinois, to Iowa;
thence, down through Western Missouri and Texas to the Gulf of Mexico;
forty-five inches from Concord, New Hampshire, through Worcester, Mass.,
Western Connecticut, and the City of New York, to the Susquehanna River,
just north of Maryland; also, at Richmond, Va., Raleigh, N. C., Augusta,
Geo., Knoxville, Tenn., Indianopolis, Ind., Springfield, Ill., St.
Louis, Mo.; thence, through Western Arkansas, across Red River to the
Gulf of Mexico. From the belt just described, the rain-fall increases
inland and southward, until at Mobile, Ala., the rain-fall is
sixty-three inches. The same amount also falls in the extreme southern
portion of Florida.
In England, the average rain-fall in the eastern portion is represented
at twenty inches; in the middle portion, twenty-two inches; in the
southern and western, thirty inches; in the extreme south-western,
forty-five inches; and in Wales, fifty inches. In the eastern portion of
Ireland, it is twenty-five inches; and in the western, forty inches.
Observations at London for forty years, by Dalton, gave average fall of
20.69 inches. Observations at New Bedford, Mass., for forty-three years,
by S. Rodman, gave average fall of 41.03 inches--about double the amount
in London. The mean quantity for each month, at both places, is as
follows:
_New Bedford._ _London._
January 3.36 1.46
February 3.32 1.25
March 3.44 1.17
April 3.60 1.28
May 3.63 1.64
June 2.71 1.74
July 2.86 2.45
August 3.61 1.81
September 3.33 1.84
October 3.46 2.09
November 3.97 2.22
December 3.74 1.74
----- ----
Spring 10.67 4.09
Summer 9.18 6.00
Autumn 10.76 6.15
Winter 10.42 4.45
----- -----
Year 41.03 20.69
Another very striking difference between the two countries is shown by a
comparison of the quantity of water falling in single days. The
following table, given in the Radcliffe Observatory Reports, Oxford,
England, 15th volume, shows the proportion of very light rains there.
The observation was in the year 1854. Rain fell on 156 days:
73 days gave less than .05 inch.
30 " between that and .10 "
27 " between .10 " .20 "
9 " " .20 " .30 "
9 " " .30 " .40 "
4 " " .40 " .50 "
1 gave .60 "
2 " .80 "
1 " 1.00 "
Nearly half the number gave less fall than five-hundredths of an inch,
and more than four-fifths the number gave less than one-fifth of an
inch, and none gave over an inch.
There is more rain in the United States, by a large measure, than there;
but the amount falls in less time, and the average of saturation is
certainly much less here. From manuscript records, furnished us by Dr.
Hobbs, of Waltham, Mass., we find, that the quantity falling in the year
1854, was equal to the average quantity for thirty years, and that rain
fell on fifty-four days, in the proportion as follows:
Number of rainy days, 54; total rain-fall, 41.29.
0 days gave less than .05 inch.
2 " between that and .10 "
8 " between .10 " .20 "
7 " " .20 " .30 "
5 " " .30 " .40 "
4 " " .40 " .50 "
2 " " .50 " .60 "
4 " " .60 " .70 "
4 " " .70 " .80 "
3 " " .80 " .90 "
0 " " .90 " 1.00 "
0 " " 1.00 " 1.10 "
2 " " 1.10 " 1.20 "
1 " " 1.20 " 1.30 "
1 " " 1.30 " 1.40 "
3 " " 1.40 " 1.50 "
2 " " 1.50 " 1.60 "
1 " " 1.60 " 1.70 "
2 " " 1.80 " 1.90 "
1 " " 2.30 " 2.40 "
1 " " 2.50 " 2.60 "
1 " " 3.20 " 3.30 "
No rain-fall gave less than five-hundredths of an inch; and more than
one-fourth the number of days gave more than one inch. In 1850, four
years earlier, the rain-fall for the year, in Waltham, was 62.13 inches,
the greatest recorded by observations kept since 1824. It fell as shown
in the table:
Number of rainy days, 58; total rain-fall, 62.13.
3 days gave between .05 and .10 inches.
4 " .10 " .20 "
6 " .20 " .30 "
3 " .30 " .40 "
5 " .40 " .50 "
3 " .50 " .60 "
3 " .60 " .70 "
3 " .70 " .80 "
2 " .80 " .90 "
1 " .90 " 1.00 "
3 " 1.00 " 1.10 "
7 " 1.20 " 1.30 "
2 " 1.80 " 1.90 "
2 " 1.90 " 2.00 "
3 " 2.00 " 2.10 "
2 " 2.10 " 2.20 "
1 " 2.30 " 2.40 "
1 " 2.50 " 2.60 "
1 " 2.60 " 2.70 "
1 " 2.80 " 2.90 "
1 " 3.60 " 3.70 "
1 " 4.50 " 4.60 "
Sept. 7th and 8th, in 24 hours, 6.88 inches of rain fell, the greatest
quantity recorded in one day.
In 1846--still earlier by four years--the rain-fall in Waltham was 26.90
inches--the least recorded by the same observations. It fell, as shown
in the table: Number of rainy days, 49; total rain-fall, 26.90.
3 days gave between .05 and .10 inches.
7 " .10 " .20 "
10 " .20 " .30 "
6 " .30 " .40 "
4 " .40 " .50 "
3 " .50 " .60 "
2 " .70 " .80 "
3 " .80 " .90 "
1 " .90 " 1.00 "
3 " 1.00 " 1.10 "
2 " 1.10 " 1.20 "
1 " 1.20 " 1.30 "
2 " 1.40 " 1.50 "
1 " 1.50 " 1.60 "
1 " 2.40 " 2.50 "
The rain-fall in 1852 was very near the average for thirty years; and
the quantity falling in single storms, on sixty-three different
occasions, as registered by Dr. Hobbs, was as follows: Number of storms,
63; total rain-fall, 42.24.
7 storms gave less than .10 inches.
11 " between .10 and .20 "
9 " " .20 " .30 "
5 " " .30 " .40 "
6 " " .40 " .50 "
5 " " .50 " .60 "
1 " " .60 " .70 "
1 " " .70 " .80 "
3 " " .80 " .90 "
1 " " .90 " 1.00 "
5 " " 1.00 " 1.10 "
1 " " 1.10 " 1.20 "
1 " " 1.20 " 1.30 "
1 " " 1.40 " 1.50 "
3 " " 1.60 " 1.70 "
1 " in 5 days 3.16 "
1 " " 4 " 4.38 "
1 " " 6 " 5.35 "
These tables are sufficient to show that provision must be made to carry
off much greater quantities of water from lands in this country than in
England. We add a table of the greatest fall of rain in any one day, for
each month, and for the year, from April, 1824, to 1st January, 1859.
It also was abstracted from the manuscript of observations by Dr. Hobbs,
and will be, we think, quite useful:
==========================================================================
YEARS |March |June |September |December
| | | | | |Greatest
| |February |May | |August |November | Fall
| | | | | | | | | | in the
|January | |April | |July| | |October | | Year
-----+----+----+----+----+----+----+----+----+----+----+----+----+--------
1824| | | |0.76|0.67|0.53|0.44|1.90|2.54|0.81|0.76|1.80| 2.54
1825|2.16| |2.61|0.27|1.23|1.37|0.91|2.51|0.89|1.32|0.71|2.40| 2.61
1826|1.80|0.56|1.67|0.89|0.39|1.78|0.87|1.80|1.57|1.37|1.22|1.41| 1.87
1827| | |3.81|1.55|2.42|0.66|1.36|3.16|4.93|2.22|3.85|1.39| 4.93
1828|0.60|1.48|1.82|2.06|2.01|1.44|1.52|0.14|1.82|1.52|1.90|0.29| 2.06
1829|3.86|1.98|4.12|2.35|1.15|0.97|1.92|0.97|1.39|1.00|1.25|1.58| 4.12
1830|1.31| |1.17|2.68|2.28|0.78|1.84|2.45|2.40|1.20|2.64|2.44| 2.68
1831|0.64|1.48|2.32|2.12|1.79|1.87|2.27|1.00|1.00|2.82|1.24|0.15| 2.82
1832|2.68|1.59|2.00|4.48|2.52|1.24| |2.13|0.80|1.50|2.60|1.34| 4.48
1833|0.83| | |2.57|0.98|2.03|1.42|0.64|2.75|2.32|3.12|1.27| 3.12
1834| |0.64|1.31|0.94|2.35|1.87|2.12|0.73|1.25|1.89|2.42|0.92| 2.42
1835|1.44|0.88|2.48|2.48|1.18|1.52|4.72|1.32|1.57|3.28|0.74|2.32| 4.72
1836|2.72|3.04|2.26|1.86|1.29|2.24|1.04|0.72|0.36|2.04|1.50|1.68| 3.04
1837|3.62|1.50|1.14|1.68|1.46|1.30|0.72|0.78|0.66|1.46|0.81|1.68| 3.62
1838|1.64|0.75|0.76|1.32|1.40|1.67|0.82|1.40|3.84|1.10|2.46|1.00| 3.84
1839|0.70|0.80|0.58|4.06|2.98|0.94|1.08|3.54|0.70|1.60|0.80|1.92| 4.06
1840|1.68|2.20|1.54|2.12|1.16|1.08|1.40|2.72|1.28|1.04|3.72|1.12| 3.72
1841|1.44|1.12|1.32|1.64|0.90|0.75|0.64|2.82|2.78|2.66|1.05|1.70| 2.82
1842|0.54|1.22|1.16|0.64|0.47|2.10|0.68|1.44|0.96|0.34|1.10|2.02| 2.10
1843|1.60|1.64|2.50|1.34|0.34|1.04|1.98|2.58|0.52|1.94|1.28| | 2.58
1844|4.14| |2.06|0.24|0.58|0.78|0.86|1.34|1.76|2.30|1.86|1.28| 4.14
1845|2.42|1.70|1.14|0.70|1.02|1.03|1.20|1.66|0.88|1.16|3.32|1.46| 3.32
1846|1.54| |2.46|1.16|1.18|0.82|1.46|0.49|0.56|0.55|0.54|1.02| 2.46
1847|1.18|2.74|1.66|1.12|0.84|1.28|0.56|1.86|2.16|0.64|2.74|3.02| 3.02
1848|1.44|1.56|2.68|0.68|2.28|1.00|0.72|1.24|1.48|2.96|0.88|1.00| 2.96
1849|1.36|0.40|2.30|0.92|1.28|0.72|1.52|2.08|1.12|2.60|2.48|1.76| 2.60
1850|2.56|1.92|1.84|2.68|2.80|1.20|1.20|3.68|6.88|1.04|2.16|1.92| 6.88
1851|0.80|1.84|0.56|3.60|1.92|1.12|0.96|0.32|1.15|1.47|2.25|0.89| 3.60
1852|1.06|0.88|1.15|4.38|1.47|1.69|0.66|4.16|1.19|1.61|1.59|0.89| 4.38
1853|0.92|1.33|1.03|1.12|2.39|0.42|1.03|2.36|2.14|1.95|1.67|1.35| 2.39
1854|0.83|1.60|1.25|1.88|2.57|1.50|1.58|0.48|2.33|1.82|3.25|1.43| 3.25
1855|3.37|3.08|0.80|1.33|0.39|1.23|1.93|0.75|0.70|1.77|2.22|1.24| 3.37
1856| |1.30|0.63|1.97|2.93|0.66|1.30|4.23|2.42|0.87|0.88|1.20| 4.23
1857|1.50|0.54|1.55|3.68|1.28|0.96|2.43|2.00|0.87|3.54|0.67|1.28| 3.68
1858|1.12|1.18|0.35|1.28|1.00|3.86|1.35|2.21|1.64|1.22|1.36|1.40| 3.86
==========================================================================
The following table shows the record of rain-fall, as kept for one year;
it was selected as a representative year, the total quantity falling
being equal to the average. For the year 1840: Number of rainy days, 50;
total rain-fall, 42.00.
======================================================================
DAYS | |March |June |September |December
| | | | |
| |February |May | |August |November
| | | | | | | | |
|January 1840 |April | |July| | |October |
-----+----+----+----+----+----+----+----+----+----+----+----+---------
1 | | | |0.55|0.14| | |2.72| |0.64| |
2 | | | | | | | |0.08| |0.05| |
3 | | |0.32| | | | | | | | |
4 | | | | | |1.08|0.10| | | | |
5 | | | | |1.16| | | |0.63| | |
6 | | | | | | | |0.50| | | |
7 | | | | | | | | | | | |
8 | | | | | |0.20| | | | | |
9 | | | | | | |0.25| | | |3.72|
10 | |2.20| | | | | | |1.28| | |
11 | | | | | | | |0.10| | | |
12 | | | |2.12| | | | | | |0.54|
13 | | | | | |0.14| | | | | |1.12
14 | |0.58| | | | | |0.70| | | |
15 | | | | | | | | | | |0.36|
16 | | | | | | | | | | | |
17 | | | | | | | | | | | |
18 | | | | | | | | | | | |
19 | | | | | |0.82|0.24| |0.68| | |1.04
20 | | |1.54| | | | | | |0.44| |
21 | | | | |0.98| | | | |1.04| |
22 | | | |0.52| | | | | | |2.20|
23 |1.68| | | | | | |0.96| | |0.18|
24 | | | | | | |1.40| | | | |
25 | | | | | | | |0.16| | |0.35|
26 | | | |0.18| | | | | | | |
27 | | | | | |0.17| | |0.30| | |
28 | | | | | | | | | | | |
29 | | | |1.80| | |0.10| | |1.40| |
30 | | |1.42| | | | | | |0.08| |1.04
31 | | | | | | | | | | | |
-----+----+----+----+----+----+----+----+----+----+----+----+---------
Total|1.68|2.78|3.28|5.17|2.28|2.41|2.09|5.22|2.89|3.65|7.35|3.20
======================================================================
The average quantity of rain which has fallen in Waltham, during the
important months of vegetation, from 1824 to 1858 inclusive--a period of
thirty-five years--is for--
_April._ _May._ _June._ _July._ _Aug._ _Sept._
3.96 3.71 3.18 3.38 4.50 3.52
Average for the six months, 22.25.
It will be noticed, that the average for the month of August is about 33
per cent. larger than for June and July. The quantity of rain falling in
each month, as registered at the Cambridge Observatory, is as follows:
MEAN OF OBSERVATIONS FOR TWELVE YEARS.
_Jan._ _Feb._ _Mar._ _Apr._ _May._ _June._
2.39 3.19 3.47 3.64 3.74 3.13
_July._ _Aug._ _Sept._ _Oct._ _Nov._ _Dec._
2.57 5.47 4.27 3.73 4.57 4.31
_Spring._ _Summer._ _Autumn._ _Winter._
10.85 11.17 12.57 9.89
Average quantity per year, 44.48.
The quantity falling from January to July, is much less than falls from
July to January.
The great quantity of snow which falls in New England during the Winter
months, and is carried off mainly in the Spring, usually floods the low
lands, and should be taken into account in establishing the size of pipe
to be used in a system of drainage. The following observations of the
average depth of snow, have been made at the places cited, and are
copied, by Blodget, from various published notices:
Oxford Co., Me. 12 years 90 inches per year.
Dover, N. H. 10 " 68.6 " "
Montreal 10 " 67 " "
Burlington, Vt. 10 " 85 " "
Worcester, Mass. 12 " 55 " "
Amherst, " 7 " 54 " "
Hartford, Conn. 24 " 43 " "
Lambertville, N. J. 8 " 25.5 " "
Cincinnati 16 " 19 " "
Burlington, Iowa 4 " 15.5 " "
Beloit, Wisconsin 3 " 25 " "
One-tenth the depth of snow is taken as its equivalent in water, for
general purposes, though it gives too small a quantity of water in
southern latitudes, and in extreme latitudes too great a quantity. The
rule of reduction of snow to water, in cold climates, is one inch of
water to twelve of snow.
The proportion of the annual downfall of rain which is collectable into
reservoirs--or, in other words, the per-centage of the rain-fall which
drains off--is well shown in a table used by Ellwood Morris, Esq., C. E.,
in an article on "The Proposed Improvement of the Ohio River" (Jour.
Frank. Inst., Jan., 1858), in which we find, that, in eighteen series of
observations in Great Britain, the ratio, or per cent. of the rain-fall
which drains off is 65-1/2, or nearly two-thirds the rain-fall.
Seven series of observations in America are cited as follows:
==========================================================================
|Name |Annual |Drainage|Ratio, or |
|of |rain-fall,|flowing |per ct. of |
No.|Drainage Area. |in inches.|away, in|the rain | Authorities.
| | |inches. |which |
| | | |drains off.|
---+---------------+----------+--------+-----------+----------------------
1 |Schuylkill | | | |
| Navigation | | | |
| Reservoirs | 36 | 18 | 50 | Morris and Smith.
2 |Eaton Brook | 34 | 23 | 66 | }
3 |Madison Brook | 35 | 18 | 50 | }McAlpine.
4 |Patroon's Brook| 46 | 25 | 55 | }
5 | " " | 42 | 18 | 42 | }
6 |Long Pond | 40 | 18 | 44 | Boston Water Com'rs.
7 |West Fork | | | |
| Reservoir | 36 | 14 | 40 | W. Milnor Roberts.
---+---------------+----------+--------+-----------+----------------------
| Totals | 269 | 134 | 347 |
| Averages | 38 | 19 | 50 |
==========================================================================
These examples show an average rain-fall of thirty-eight vertical
inches, and an annual amount, collectable in reservoirs, of nineteen
inches, or fifty per cent.
The per-centage of water of drainage from land under-drained with tile,
would be greater than that which is collectable in reservoirs from
ordinary gathering-grounds.
If a soil were perfectly saturated with water, that is, held as much
water in suspension as possible to hold without draining off, and drains
were laid at a proper depth from the surface, and in sufficient number
to take off all surplus water, then the entire rain-fall upon the
surface would be water of drainage--presuming, of course, the land to be
level, and the air at saturation, so as to prevent evaporation. The
water coming upon the surface, would force out an equal quantity of
water at the bottom, through the drains--the time occupied by the
process, varying according to the porous or retentive nature of the
soil; but in ordinary circumstances, it would be, perhaps, about
forty-eight hours. Drains usually run much longer than this after a
heavy rain, and, in fact, many run constantly through the year, but they
are supplied from lands at a higher level, either near by or at a
distance.
If, on the other hand, the soil were perfectly dry, holding no water in
suspension, then there would be no water of drainage until the soil had
become saturated.
Evaporation is constantly carrying off great quantities of water during
the warm months, so that under-drained soil is seldom in the condition
of saturation, and, on account of the supply by capillary attraction and
by dew, is never thoroughly dry; but the same soil will, at different
times, be at various points between saturation and dryness, and the
water of drainage will be consequently a greater or less per centage of
the rain-fall.
An experiment made by the writer, to ascertain what quantity of water a
dry soil would hold in suspension, resulted as follows: A soil was
selected of about average porosity, so that the result might be, as
nearly as possible, a mean for the various kinds of soil, and dried by
several days' baking. The quantity of soil then being carefully
measured, a measured quantity of water was supplied slowly, until it
began to escape at the bottom. The quantity draining away was measured
and deducted from the total quantity supplied. It was thus ascertained
that one cubic foot of earth held 0.4826+ cubic feet of water, which is
a little more than three and one-half gallons. A dry soil, four feet
deep, would hold a body of water equal to a rain-fall of 23.17 inches,
vertical depth, which is more than would fall in six months.
The quantity which is not drained away is used for vegetation or
evaporated; and the fact, that the water of drainage is so much greater
in proportion to the rain-fall in England than in this country, is owing
to the humidity of that climate, in which the evaporation is only about
half what it is in this country.
The evaporation from a reservoir surface at Baltimore, during the Summer
months, was assumed by Colonel Abert to be to the quantity of rain as
two to one.
Dr. Holyoke assigns the annual quantity evaporated at Salem, Mass., at
fifty-six inches; and Colonel Abert quotes several authorities at
Cambridge, Mass., stating the quantity at fifty-six inches. These facts
are given by Mr. Blodget, and also the table below.
QUANTITY OF WATER EVAPORATED, IN INCHES, VERTICAL DEPTH.
| Whitehaven, | |
| England, | Ogdensburg, | Syracuse,
| mean of | N. Y., | N. Y.,
| 6 years | 1 yr. | 1 year
--------+-------------+-------------+------------
_Jan._ | 0.88 | 1.65 | 0.67
_Feb._ | 1.04 | 0.82 | 1.48
_Mar._ | 1.77 | 2.07 | 2.24
_Apr._ | 2.54 | 1.63 | 3.42
_May._ | 4.15 | 7.10 | 7.31
_June._ | 4.54 | 6.74 | 7.60
_July._ | 4.20 | 7.79 | 9.08
_Aug._ | 3.40 | 5.41 | 6.85
_Sept._ | 3.12 | 7.40 | 5.33
_Oct._ | 1.93 | 3.95 | 3.02
_Nov._ | 1.32 | 3.66 | 1.33
_Dec._ | 1.09 | 1.15 | 1.86
--------+-------------+-------------+------------
_Year._ | 30.03 | 49.37 | 50.20
The quantity for Whitehaven, England, is reported by J. F. Miller. It
was very carefully observed, from 1843 to 1848--the evaporation being
from a copper vessel, protected from rain. The district is one of the
wettest of England--the mean quantity of rain, for the same time, having
been 45.25 inches.
This shows a great difference in the capacity of the air to absorb
moisture in England and the United States; and as evaporation is a
cooling process, there is greater necessity for under-draining in this
country than in England, supposing circumstances in other respects to be
similar.
Evaporation takes place at any point of temperature from 32 deg., or lower,
to 212 deg.--at which water boils. It is increased by heat, but is not
caused solely by it--for a north-west wind in New-England evaporates
water, and dries the earth more rapidly than the heat alone of a
Summer's day; and when, under ordinary circumstances, evaporation from a
water-surface is slow, it becomes quite active when brought in close
proximity to sulphuric acid, or other vapor-absorbing bodies.
The cold which follows evaporation is caused by a loss of the heat which
is required for evaporation, and which passes off with the vapor, as a
solution, in the atmosphere; and as heat leaves the body to aid
evaporation, it is evident that that body cannot be cooled by the
process, below the dew-point at which evaporation ceases. The popular
notion that a body may be cooled almost to the freezing-point, in a hot
Summer day, by the action of heat alone, is, then, erroneous. But still,
the amount of heat which is used up in evaporating stagnant water from
undrained land, that might otherwise go towards warming the land and the
roots of crops, is a very serious loss.
The difference in the temperature of a body, resulting from evaporation,
may reach 25 deg. in the desert interior of the American continent; but, in
the Eastern States, it is not often more than 15 deg..
The temperature of evaporation is the reading of a wet-bulb-thermometer
(the bulb being covered with moistened gauze) exposed to the natural
evaporation; and the difference between that reading and the reading of
a dry-thermometer, is the expression of the cold resulting from
evaporation.
When the air is nearly saturated, the temperature of the air rarely goes
above 74 deg.; but, if so, the moisture in the air prevents the passing away
of insensible perspiration, and the joint action of heat and humidity
exhausts the vital powers, causing sun-stroke, as it is called. At New
York city, August 12th to 14th, 1853, the wet-thermometer stood at 80 deg.
to 84 deg.; the air, at 90 deg. to 94 deg.. The mortality, from this joint effect,
was very great--over two hundred persons losing their lives in the two
days, in that city.
From very careful observations, made by Lorin Blodget, in 1853, at
Washington, it was found that the difference between the wet and dry
thermometer was 18-1/2 deg. at 4 P. M., June 30th, and 16 deg. at 2 P. M. on
July 1st--the temperature of the air being 98 deg. on the first day, and 95 deg.
on the second; but such excesses are unusual.
The following table has been compiled from Mr. Blodget's notice of the
peculiarities of the Summer of 1853:
The dates are such as were selected to illustrate the extreme
temperatures of the month, and the degrees represent the differences
between the wet and dry thermometer. The observations were made at 3 P. M.:
_Locality._ _Dates._ _Differences._
JUNE, 1853.
Burlington, Vt. 14th to 30th ranged from 8 deg. to 17 deg.
Montreal 14th to 30th " 6 to 17
Poultney, Iowa 10th to 30th " 9 to 16
Washington 20th to 30th " 8.5 to 16
Baltimore 13th to 30th " 7.4 to 20.2
Savannah 13th to 30th " 5.2 to 17.3
Austin, Texas 10th to 30th " 4 to 24
Clarkesville, Tenn. 4th to 30th " 10.3 to 20.5
AUGUST.
Bloomfield, N. J. 9th to 14th " 5 to 15
Austin, Texas 6th to 12th " 0 to 19
Philadelphia 10th to 15th " 8 to 14
Jacksonville, Fla. 10th to 15th " 6 to 8
Observations by Lieut. Gillis, at Washington, give mean differences
between wet and dry thermometers, from March, 1841, to June, 1842, as
follows:
Observations at 3 P. M.:
_Jan._ _Feb._ _Mar._ _Apr._ _May._ _June._
3 deg..08 4 deg..40 6 deg..47 5 deg..37 7 deg..05 8 deg..03
_July._ _Aug._ _Sept._ _Oct._ _Nov._ _Dec._
8 deg..89 5 deg..29 5 deg..63 4 deg..61 4 deg..77 2 deg..03
A mean of observations for twenty-five years at the Radcliffe
Observatory, Oxford, England, gives a difference between the wet and dry
thermometer equal to about two-thirds the difference, as observed by
Lieutenant Gillis, at Washington.
On the 12th day of August, 1853, in Austin, Texas, the air was perfectly
saturated at a temperature of 76 deg., which was the dew-point, or point of
the thermometer at which dew began to form. The dew-point varies
according to the temperature and the humidity of the atmosphere; it is
usually a few degrees lower than the temperature of evaporation--never
higher.
From observations made at Girard College, by Prof. A. D. Bache, in the
years 1840 to 1845, we find, that for April, 1844, the dew-point ranged
from 4 deg. to 16 deg. lower than the temperature of the air; in May, from 4 deg. to
14 deg. lower; in June, from 6 deg. to 20 deg. lower; in July, from 4 deg. to 17 deg.; in
August, from 6 deg. to 15 deg. lower; and in September, from 6 deg. to 21 deg. lower.
The dew-point is, then, during the important months of vegetation,
within about 20 deg. of the temperature of the air. The temperature of the
dew-point, as observed by Prof. Bache, was highest in August, 1843,
being 66 deg., and lowest in January, 1844, being 18 deg.; in July, 1844, it was
64 deg., and in February, 1845, it was 25 deg.. Its hourly changes during each
day are quite marked, and follow, with some degree of regularity, the
changes in the temperature of the air; their greatest departure from
each other being at the hottest hour of the day, which is two or three
hours after noon, and the least at the coldest hour which is four or
five hours after midnight. The average temperature of the dew-point in
April, May, and June, 1844, was, at midnight, 50-1/2 deg., air, 57 deg.; five
hours after midnight, dew-point, 49 deg., air 54 deg.; three hours after noon,
dew-point, 54 deg., air, 63-1/2 deg.. The average temperature for July, August
and September, was, at midnight, dew-point, 58-1/2 deg., air, 65 deg.; five
hours after midnight, dew-point, 58 deg., air, 62 deg.; three hours after noon,
dew-point, 60-1/2 deg., air, 78 deg.. The average temperature for the year was,
at midnight, dew-point, 42 deg., air, 48 deg.; five hours after midnight,
dew-point, 41 deg., air, 46 deg.; three hours after noon, dew-point, 44-1/2 deg.,
air, 59 deg..
The relative humidity of the atmosphere, or the amount of vapor held in
suspension in the air, in proportion to the amount which it might hold,
was, in the year 1858, as given in the journal of the Franklin
Institute, for
_Philadelphia._ _Somerset Co._
April 49 per cent. -- 2 P. M.
May 59 " 72 "
June 55 " 63 "
July 50 " 61 "
August 55 " 58 "
September 50 " 57 "
The saturation often falls to 30 per cent., but with great variability.
Evaporation goes on most rapidly when the per centage of saturation is
lowest; and, as before observed, the cause of the excess of evaporation
in this country over that of England is the excessive humidity of that
climate and the dryness of this. It has also been said that there is
greater need for drainage in the United States on this account; and, as
the warmth induced by draining is somewhat, in its effect, a
merchantable product, it may be well to consider it for a moment in that
light.
First: The drained land comes into condition for working, a week or ten
days earlier in the Spring than other lands.
Secondly: The growth of the crops is quickened all through the Summer by
an increase of several degrees in the temperature of the soil.
Thirdly: The injurious effects of frost are kept off several days later
in the Fall.
Of the value of these conditions, the farmer, who has lost his crops for
lack of a few more warm days, may make his own estimates. In Roxbury,
Mr. I. P. Rand heats up a portion of his land, for the purpose of
raising early plants for the market, by means of hot water carried by
iron pipes under the surface of the ground. In this manner he heats an
area equal to 100 feet by 12 feet, by burning about one ton of coal a
month. The increase of temperature which, in this case, is caused by
that amount of coal, can, in the absence of direct measurement, only be
estimated; but it, probably, will average about 30 deg., day and night,
throughout the month. In an acre the area is 36.4 times as great as that
heated by one ton of coal; the cost being in direct proportion to the
area, 36.4 tons of coal would be required to heat an acre; which, at $6
per ton, would cost $217.40. To heat an acre through 10 deg., would cost,
then, $72.47. It may be of interest to consider how much coal would be
required to evaporate from an undrained field that amount of water which
might be carried off by under-drains, but which, without them, is
evaporated from the surface. It may be taken as an approximate estimate,
that the evaporation from the surface of an undrained retentive field,
is equal to two inches vertical depth of water for each of the months of
May, June, July, and August; which is equal to fifty-four thousand three
hundred and five gallons, or eight hundred and sixty-two hogsheads per
acre for each month. If this quantity of water were evaporated by means
of a coal fire, about 22-2/3 tons of coal would be consumed, which, at
$6 a ton, would cost $136. The cost of evaporating the amount of water
which would pass off in one day from an acre would be about $4.53. It is
probable that about half as much water would be evaporated from
thorough-drained land, though, by some experiments, the proportion has
been made greater--in which case the loss of heat resulting from an
excess of moisture evaporated from undrained retentive land, over that
which would be evaporated from drained land, would be equal to that
gained by 11-1/3 tons of coal, which would cost $68; and this for each
acre, in each of the three months. At whatever temperature a liquid
vaporizes, it absorbs the same total quantity of heat.
The latent heat of watery vapor at 212 deg. is 972 deg.; that is, when water at
212 deg. is converted into vapor at the same temperature, the amount of heat
expended in the process is 972 deg.. This heat becomes latent, or insensible
to the thermometer. The heat rendered latent by converting ice into
water is about 140 deg.. There are 7.4805 gallons in a cubic foot of water
which weighs 62.38 lbs."
We have seen that a sea of water, more than three feet deep over the
whole face of the land, falls annually from the clouds, equal to 4,000
tons in weight to every acre. We would use enough of this water to
dissolve the elements of fertility in the soil, and fit them for the
food of plants. We would retain it all in our fields, long enough to
take from it its stores of fertilizing substances, brought from reeking
marshes and steaming cities on cloud-wings to our farms. We would, after
taking enough of its moisture to cool the parched earth, and to fit the
soil for germination and vegetable growth, discharge the surplus, which
must otherwise stagnate in the subsoil, by rapid drainage into the
natural streams and rivers.
Evaporation proceeds more rapidly from a surface of water, than from a
surface of land, unless it be a saturated surface. It proceeds more
rapidly in the sun than in the shade, and it proceeds again more rapidly
in warm than in cold weather. It varies much with the culture of the
field, whether in grass, or tillage, or fallow, and with its condition,
as to being dry or wet, and with its formation, whether level or hilly.
Yet, with all these variations, very great reliance may be placed upon
the ascertained results of the observations already at our command.
We have seen that evaporation from a water surface is, in general,
greater than from land, and here we may observe one of those grand
compensating designs of Providence which exist through all nature.
If the same quantity of water fell upon the sea and the land, and the
evaporation were the same from both, then all the rivers running into
the sea would soon convey to it all the water, and the sea would be
full. But though nearly as much water falls on the sea as on the land,
yet evaporation is much greater from the water than from land.
About three feet of rain falls upon the _water_, while the evaporation
from a water surface far exceeds that amount. In the neighborhood of
Boston, evaporation from water surface is said to be 56 inches in the
year, and in the State of New York, about 50 inches; while, in England,
it is put by Mr. Dalton at 44.43 inches, and, by others, much lower.
Again, about three feet of water annually falls upon the _land_, while
the evaporation from the land is but little more than 20 inches. If this
water fell upon a flat surface of soil, with an impervious subsoil of
rock or clay, we should have some sixteen inches of water in the course
of the year more than evaporates from the land. If a given field be
dish-shaped, so as to retain it all, it must become a pond, and so
remain, except in Summer, when greater evaporation from a water surface
may reduce it to a swamp or marsh.
With 16 or 18 inches more water falling annually on all our cultivated
fields than goes off by evaporation, is it not wise to inquire by what
process of Nature or art this vast surplus shall escape?
Experiments have been made with a view to determine the proportion of
evaporation and filtration, upon well-drained land, in different months.
From an able article in the N. Y. Agricultural Society for 1854, by
George Geddes, we copy the following statement of valuable observations
upon these points.
It will be observed that, in the different observations collected in
this chapter, results are somewhat various. They have been brought
together for comparison, and will be found sufficiently uniform for all
practical purposes in the matter of drainage.
"The experiments upon evaporation and drainage, made on Mr.
Dalton's plan, were in vessels three feet deep, filled with soil
just in the condition to secure perfect freedom from excess of
water, and the drainage was determined by the amount of water that
passed out of the tube at the bottom. These experiments have been
most perfectly made in England by Mr. John Dickinson. The following
table exhibits the mean of eight years:
======================================================================
YEAR.| October to March. || April to September.|| Total each year.
-----|--------------------||--------------------||--------------------
|Rain.|Filtra-| [%] ||Rain.|Filtra-| [%] ||Rain.|Filtra-| [%]
| | tion. | || | tion. | || | tion. |
-----|--------------------||--------------------||--------------------
1836 |18.80| 15.55 | 82.7 ||12.20| 2.10 | 17.3 ||31.00| 17.65 | 56.9
1837 |11.30| 6.85 | 60.6 || 9.80| 0.10 | 1.0 ||21.10| 6.95 | 32.9
1838 |12.32| 8.45 | 68.8 ||10.81| 0.12 | 1.2 ||23.13| 8.57 | 37.0
1839 |13.87| 12.31 | 88.2 ||17.41| 2.60 | 15.0 ||31.28| 14.91 | 47.6
1840 |11.76| 8.19 | 69.6 || 9.68| 0.00 | 0.0 ||21.44| 8.19 | 38.2
1841 |16.84| 14.19 | 84.2 ||15.26| 0.00 | 0.0 ||32.10| 14.19 | 44.2
1842 |14.28| 10.46 | 73.2 ||12.15| 1.30 | 10.7 ||26.43| 11.76 | 44.4
1843 |12.43| 7.11 | 57.2 ||14.04| 0.99 | 7.1 ||26.47| 8.10 | 36.0
-----|--------------------||--------------------||--------------------
Mean |13.95| 10.39 | 74.5 ||12.67| 0.90 | 7.1 ||26.61| 11.29 | 42.4
======================================================================
Legend: [%] = Per cent filtered.
"A soil that holds no water for the use of plants below six inches,
will suffer from drouth in ten days in June, July, or August. If
the soil is in suitable condition to hold water to the depth of
three feet, it would supply sufficient moisture for the whole
months of June, July, and August.
"M. de la Hire has shown that, at Paris, a vessel, sixteen inches
deep, filled with sand and loam, discharged water through the pipe
at the bottom until the 'herbs' were somewhat grown, when the
discharge ceased, and the rains were insufficient, and it was
necessary to water them. The fall of water at Paris is stated, in
this account, at twenty inches in the year, which is less than the
average, and the experiment must have been made in a very dry
season; but the important point proved by it is, that the plants,
when grown up, draw largely from the ground, and thereby much
increase the evaporation from a given surface of earth. The result
of the experiment is entirely in accordance with what would have
been expected by a person conversant with the laws of vegetation.
"The mean of each month for the eight years is:
==============================================
| | |Per cent
MONTHS. | Rain. |Filtration.|
| | |filtered.
-------------+---------+-----------+----------
|_Inches._| _Inches._ |
| | |
January | 1.84 | 1.30 | 70.7
February | 1.79 | 1.54 | 78.4
March | 1.61 | 1.08 | 66.6
April | 1.45 | 0.30 | 21.0
May | 1.85 | 0.11 | 5.8
June | 2.21 | 0.04 | 1.7
July | 2.28 | 0.04 | 1.8
August | 2.42 | 0.03 | 1.4
September | 2.64 | 0.37 | 13.9
October | 2.82 | 1.40 | 49.5
November | 3.83 | 3.26 | 84.9
December | 1.64 | 1.80 | 110.0
==============================================
"The filtration from April to September is very small--practically
nothing; but during those months we have 12.67 inches of rain--that
is, we have two inches a month for evaporation besides the quantity
in the earth on the first day of April. From October to March we
have 10.39 inches filtered out of 13.95 inches, the whole fall. 'Of
this Winter portion of 10.39, we must allow at least six inches for
floods running away at the time of the rain, and then we have only
4.39 inches left for the supply of rivers and wells.' (Breadmore,
p. 34.)
"It is calculated in England that the ordinary Summer run of
streams does not exceed ten cubic feet per minute per square mile,
and that the average for the whole year, due to springs and
ordinary rains, is twenty feet per minute per square mile,
exclusive of floods--and assuming no very wet or high mountain
districts (Breadmore, p. 34)--which is equal to about four inches
over the whole surface. If we add to this the six inches that are
supposed to run off in freshets, we have ten inches discharged in
the course of the year by the streams. The whole filtration was
11.29 inches--10.39 in the Winter, and .90 in the Summer. The
remainder, 1.29 inches, is supposed to be consumed by wells and
excessive evaporation from marshes and pools, from which the
discharge is obstructed, by animals, and in various other ways.
These calculations were made from experiments running through eight
years, in which the average fall of water was only 26.61 inches per
annum. When the results derived from them are applied to our
average fall of 35.28 inches, we have for the water that
constitutes the Summer flow of our streams 13.25 cubic feet per
minute per mile of the country drained, and for the average annual
flow, exclusive of freshets, 26.50 cubic feet per mile per minute.
That is to say, of the 35.28 inches of water that fall in the
course of the year, 5.30 run away in the streams as the average
annual flow, 7.95 run away in the freshets, and 20.47 evaporate
from the earth's surface, leaving 1.56 for consumption in various
ways. In the whole year the drainage is nearly equal to one cubic
foot per second per square mile (.976), no allowance being made for
the 1.56 inches which is lost as before stated. These calculations
are based upon English experiments. Mr. McAlpine, late State
engineer and surveyor, in making his calculations for supplying the
city of Albany with water (page 22 of his Report to the Water
Commissioners), takes 45 per cent of the fall as available for the
use of the city. Mr. Henry Tracy, in his Report to the Canal Board
of 1849 (page 17), gives the results of the investigations in the
valleys of Madison Brook, in Madison County, and of Long Pond, near
Boston, Mass., as follows:
==========================================================================
| Name | Fall of rain | Water ran off | Evaporation | Ratio
YEAR. | of | and snow | in | from surface | of
| valley. | in valley. | inches. | of ground. | drainage.
----------------+--------------+---------------+--------------+-----------
1835 | Madison | | | |
| Brook | 35.26 | 15.83 | 19.43 | 0.449
------+---------+--------------+---------------+--------------+-----------
1837 | Long | | | |
| Pond | 26.65 | 11.70 | 14.95 | 0.439
------+---------+--------------+---------------+--------------+-----------
1838 | Do | 38.11 | 16.62 | 21.49 | 0.436
------+---------+--------------+---------------+--------------+-----------
Mean | | | | | 0.441
==========================================================================
"Madison Brook drains 6,000 acres, and Long Pond 11,400 acres. Mr.
Tracy makes the following comment on this table: 'It appears that
the evaporation from the surface of the ground in the valley of
Long Pond was about 44 per cent more in 1838 than it was in 1837,
while the ratio of the drainage differed less than one per cent the
same years.'
"Dr. Hale states the evaporation from water-surface at Boston to be
56 inches in a year. (Senate Doc., No. 70, for 1853.)
"The following table contains the results arrived at by Mr. Coffin,
at Ogdensburgh, and Mr. Conkey, at Syracuse, in regard to the
evaporation from water-surface:
=============================================================
| COFFIN, at Ogdensburgh,|| CONKEY, at Syracuse,
| in 1838. || in 1852.
MONTHS. +--------+---------------++--------+--------------
| Rain. | Evaporation. || Rain. | Evaporation.
-----------+--------+---------------++--------+--------------
January | 2.36 | 1.652 || 3.673 | 0.665
February | 0.97 | 0.817 || 1.307 | 1.489
March | 1.18 | 2.067 || 3.234 | 2.239
April | 0.40 | 1.625 || 3.524 | 3.421
May | 4.81 | 7.100 || 4.491 | 7.309
June | 3.57 | 6.745 || 3.773 | 7.600
July | 1.88 | 7.788 || 2.887 | 9.079
August | 2.55 | 5.415 || 2.724 | 6.854
September | 1.01 | 7.400 || 2.774 | 5.334
October | 2.73 | 3.948 || 4.620 | 3.022
November | 2.07 | 3.659 || 4.354 | 1.325
December | 1.08 | 1.146 || 4.112 | 1.863
-----------+--------+---------------++--------+--------------
TOTAL | 24.61 | 49.362 || 41.473 | 50.200
=============================================================
"The annual fall of water in England, is stated, by Mr. Dalton, to
be 32 inches. In this State, it is 35.28 inches. The evaporation
from water-surface in England, is put, by Mr. Dalton, at 44.43
inches. The fall is less, and the evaporation is less, in England
than here; and the fall, in each case, bears the same proportion to
the evaporation, very nearly; and it appears that the experiments
made on the two sides of the ocean, result in giving very nearly
the same per centage of drainage. In England, it is 42.4 per cent.;
in this State, it is 44.1. In England, the experiments were made on
a limited scale compared with ours; but the results agree so well,
that great confidence may safely be placed in them."
In reviewing the whole subject of rain, and of evaporation and
filtration, we seem to have evidence to justify the opinion, that with
considerable more rain in this country than in England, and with a
greater evaporation, because of a clearer sky and greater heat, we have
a larger quantity of surplus water to be disposed of by drainage.
The occasion for thorough-drainage, however, is greater in the Northern
part of the United States than in England, upon land of the same
character; because, as we have already seen, rain falls far more
regularly there than here, and never in such quantities in a single day;
and because there the land is open to be worked by the plough nearly
every day in the year, while here for several months our fields are
locked up in frost, and our labor for the Spring crowded into a few
days. There, the water which falls in Winter passes into the soil, and
is drained off as it falls; while here, the snow accumulates to a great
depth, and in thawing floods the land at once.
Both here and in England, much of the land requires no under-draining,
as it has already a subsoil porous enough to allow free passage for all
the surplus water; and it is no small part of the utility of
understanding the principles of drainage, that it will enable farmers to
discriminate--at a time when draining is somewhat of a fashionable
operation with amateurs--between land that does and land that does _not_
require so expensive an operation.