because, under this condition, evaporation is less activa Such lands, in cloudy weather, form an unnatural growth, such as results in the "lodging" of grain crops, from the deficient strength of the straw which this growth produces.

In hot weather, the temperature of the lower soil is, of course, much lower than that of the air, and lower than that of the water of warm rains. If the soil is saturated with water, the water will, of course, be of an even temperature with the soil in which it lies, but if this be drained off, warm air will enter from above, and give its heat to the soil, while each rain, as it falls, will also carry its heat with it. Furthermore, the surface of the ground is sometimes excessively heated by the summer sun, and the heat thus contained is carried down to the lower soil by the descending water of rains, which thus cool the surface and warm the subsoil, both beneficial.

66

Mr. Josiah Parkes, one of the leading draining engi neers of England, has made some experiments to test the extent to which draining affects the temperature of the soil. The results of his observations are thus stated by Gisborne: "Mr. Parkes gives the temperature on a "Lancashire flat moss, but they only commence 7 inches "below the surface, and do not extend to mid-summer. "At that period of the year the temperature, at 7 inches, never exceeded 66°, and was generally from 10° to 15° "below the temperature of the air in the shade, at 4 feet "above the earth. Mr. Parkes' experiments were made "simultaneously, on a drained, and on an undrained por ❝tion of the moss; and the result was, that, on a mean "of 35 observations, the drained soil at 7 inches in depth was 10° warmer than the undrained, at the same depth. "The undrained soil never exceeded 47°, whereas, after a "thunder storm, the drained reached 66° at 7 inches, and "48° at 31 inches. Such were the effects, at an early period of the year, on a black bog. They suggest some

66

66

" idea of what they were, when, in July or August, thunder "rain at 60° or 70° falls on a surface heated to 130°, and "carries down with it, into the greedy fissures of the earth, "its augmented temperature. These advantages, porous "soils possess by nature, and retentive ones only acquire "them by drainage."

Drained land, being more open to atmospheric circulation, and having lost the water which prevented the tem perature of its lower portions from being so readily affected by the temperature of the air as it is when dry, will freeze to a greater depth in winter and thaw out earlier in the spring. The deep freezing has the effect to greatly pulverize the lower soil, thus better fitting it for the support of vegetation; and the earlier thawing makes it earlier ready for spring work.

Drought. At first thought, it is not unnatural to sup pose that draining will increase the ill effect of too dry seasons, by removing water which might keep the soil moist. Experience has proven, however, that the result is exactly the opposite of this. Lands which suffer most from drought are most benefited by draining,-more in their greater ability to withstand drought than in any other particular. This applies to heavy soils.

The reasons for this action of draining become obvious, when its effects on the character of the soil are examined. There is always the same amount of water in, and about, the surface of the earth. In winter there is more in the soil than in summer, while in summer, that which has been dried out of the soil exists in the atmosphere in the form of a vapor. It is held in the vapory form by heat, which may be regarded as braces to keep it distended. When vapor comes in contact with substances sufficiently colder than itself, it gives up its heat, thus losing its braces, contracts, becomes liquid water, and is deposited as dew.

Many instrances of this operation are familiar to all.

For instance, a cold pitcher in the summer robs the vapor in the air of its heat, and causes it to be deposited on its own surface, of course the water comes from the atmosphere, not through the wall of the pitcher; if we breathe on a knife blade, it condenses, in the same manner, the moisture of the breath, and becomes covered with a film of water; stone-houses are damp in summer, because the inner surface of their walls, being cooler than the atmosphere, causes its moisture to be deposited in the manner described ;* nearly every night, in summer, the cold earth receives moisture from the atmosphere in the form of dew; a single large head of cabbage, which at night is very cold, often condenses water to the amount of a gill or more.

The same operation takes place in the soil. When the air is allowed to circulate among its lower and cooler, (because more shaded,) particles, they receive moisture by . the same process of condensation. Therefore, when, by the aid of under-drains, the lower soil becomes sufficiently loose and open to allow a circulation of air, the deposit of atmospheric moisture will keep it supplied with water, at a point easily accessible to the roots of plants.

If we wish to satisfy ourselves that this is practically correct, we have only to prepare two boxes of finely pul verized soil,-one three or four inches deep,-and the other fifteen or twenty inches deep, and place them in the sun, at midday, in summer. The thinner soil will soon be completely dried, while the deeper one, though it may have been previously dried in an oven, will soon accumulate a

By leaving a space between the wall and the plastering, this moisture is prevented from being an annoyance, and if the inclosed space is not pen from top to bottom, so as to allow a circulation of air, but little vapor will come in contact with the wall, and but an inconsiderable amount will be deposited.

large amount of water on those particles which, being lower and better sheltered from the sun's heat than the particles of the thin soil, are made cooler.

We have seen that even the most retentive soil,—the stiffest clay, is made porous by the repeated passage of water from the surface to the level of the drains, and that the ability to admit air, which plowing gives it, is maintained for a much longer time than if it were usually saturated with water which has no other means of escape than by evaporation at the surface. The power of dry soils to absorb moisture from the air may be seen by an examination of the following table of results obtained by Schuebler, who exposed 1,000 grains of dried soil of the various kinds named to the action of the air:

The effect of draining in overcoming drought, by admit ting atmospheric vapor will, of course, be very much increased if the land be thoroughly loosened by cultivation, and especially if the surface be kept in an open and mellow condition.

་

In addition to the moisture received from the air, as above described, water is, in a porous soil, drawn up from the wetter subsoil below, by the same attractive force which acts to wet the whole of a sponge of which only the lower part touches the water;-as a hard, dry, compact sponge will absorb water much less readily than one which is loose and open, so the hard clods, into which undrained clay is dried, drink up water much less freely than they will do after draining shall have made them more friable.

66

The source of this underground moisture is the water table," the level of the soil below the influence of the

drains,--and this should be so placed that, while its water will easily rise to a point occupied by the feeding roots of the crop, it should yield as little as possible for evapora tion at the surface.

Another source of moisture, in summer, is the deposit of dew on the surface of the ground. The amount of this is very difficult to determine, and accurate American experi ments on the subject are wanting. Of course the amount of dew is greater here than in England, where Dr. Dalton, a skillful examiner of atmospheric phenomena, estimates the annual deposit of dew to equal a depth of five inches, or about one-fifth of the rain-fall. Water thus deposited on the soil is absorbed more or less completely, in propor tion to the porosity of the ground.

The extent to which plants will be affected by drought depends, other things being equal, on the depth to which they send their roots. If these lie near the surface, they will be parched by the heat of the sun. If they strike deeply into the damper subsoil, the sun will have less effect on the source from which they obtain their moisture. Nothing tends so much to deep rooting, as the thorough draining of the soil. If the free water be withdrawn to a considerable distance from the surface, plants,-even without the valuable aid of deep and subsoil plowing,will send their roots to great depths. Writers on this subject cite many instances in which the roots of ordinary crops "not mere hairs, but strong fibres, as large as packthread," sink to the depth of 4, 6, and in some instances 12 or 14 feet. Certain it is that, in a healthy, well aerated soil, any of the plan's ordinarily cultivated in the garden or field will send their roots far below the parched surface soil, bu if the subsoil is wet, cold, and soggy, at the time when the young crop is laying out its plan of future action, it will perforce accommodate its roots to the limited space which the comparatively dry surface soil

affords.