of the field, lest they should burst, from being overcharged with water; but by making them of suitable capacity, no such danger need be apprehended, and therefore their use may be dispensed with. In the absence of a proper instrument, the fall of the drain is ascertained by the direction of the water in the bottom of the drain; but when the drain is dry, a bucket of water thrown on the bottom, after having been cleared out, will at once indicate the fall. Mr. Smith mentions that a fall of four inches in a mile will be sufficient to carry off the water.

6

When tiles are used, the drains need not be so deep as when filled with broken stones. The figure in the margin represents a drain with a tile, through which the water passes. In England and Scotland, draining tiles are very common, and a source of considerable profit to the manufacturer; but in Ireland not a single tile is manufactured, that we are aware of, except at the Earl of Courtown's, near Gorey, in the county of Wexford. Many parts of Ireland are supplied with clay fit for making not only draining tiles, but fire bricks, and coarse ware of every description. Now that draining is becoming more general in Ireland, a good demand may be had for tiles, which, if manufactured in districts where stones are scarce, would pay well. In the absence of flags or stones, or where the expense of procuring tiles is beyond the reach of the occupier, the surface sod should be inverted, and laid on the shoulders prepared to receive it, as represented by the cut in page 272, leaving sufficient room beneath for the water to pass away. This will answer very well for

many years; but when the sods sink to the bottom of the drain, and choke it up, the process must be repeated, by removing the obstruction, or making a new drain. The failure of the old drain is generally indicated by the water which comes to the surface, in the vicinity of the deranged part of the drain : such drains are very common in many parts of the county of Limerick, especially in the small county.

In draining land, it is always necessary to ascertain the direction of the slope or fall of the ground, which can always be determined by means of the levelling instrument described in the preceding part of this work; but as the price of this instrument is beyond the reach of many practical drainers, and its use known to but very few of that class, a cheap and simple level may be obtained of any of the Dublin opticians, which will be found to answer all the purposes of the practical drainer, whose principal object is to ascertain the direction of the fall, and not its amount. The instrument, which is furnished with a bubble, is placed on the top of a four-legged stool, and levelled by raising or depressing the end or side of the little stool or table, till the bubble be made to stand in the middle of it. The instrument being levelled, a person with a staff is sent in different directions, and holding it at different points, in a perpendicular position, the man at the instrument viewing it along the upper surface of the little table, at once discovers the direction of the fall, which is indicated by the visual ray cutting the staff at a higher point. When the visual ray cuts the staff at a lower point, viewing it along the upper surface of the table, there is a rise in the ground from the table in the direction

of the staff.

In the case where whins or similar materials are used as ducts, they should invariably be covered with scraws or peat moss, well pressed, in order to prevent the water from entering at the top of the drain, which, no doubt, would carry with it particles of sand or clay, that would ultimately choke up the drain, and prevent the free passage of the water through it. When the water enters the drain by the sides, it is deprived of any sedimentary matter in its descent from the surface, through the fissures or cracks which must necessarily take place in the substratum, after the drainage has been effected.

When the slope or inclination of a drain, only of sufficient capacity to void the water, diminishes, the velocity of the water necessarily diminishes also. And as the transverse section of the drain varies inversely as the velocity of the water passing through it, it follows that where the inclination of the drain diminishes, the breadth must increase so as to be inversely as the velocity of the water; and on the contrary, where the drain becomes more precipitous, the breadth may be diminished, so as to make the cross-section still inversely as the velocity of the water passing through the drain. This is only intended to apply to cases where the quantity of water is considerable, and the drains apt to be completely full. When the quantity of water is small, and the drain not likely to be, at any time, entirely full, then it may be made of uniform breadth throughout, no fear being apprehended of its blowing up.

The plough is sometimes employed, with good effect, in making the frequent drains, which require, however, to be dressed up with the spade, as no application of the plough could finish the sides.

The scientific agriculturist will not allow the water, collected by his drains, to escape from his farm without turning it to some account. In most farms, it may be employed in irrigating some parts of them, which would have a beneficial effect, as shall be shewn further on, in the article on irrigation.

Wherever the scale is not represented, the cuts are not laid down to any particular scale.

SUBSOIL PLOUGHING OR DIGGING.

A thorough drainage having been completed, its effects upon the subsoil will soon become visible. The excessive moisture in the vicinity of the drains being drawn away, the subsoil begins to crack in those parts, owing to the contraction which necessarily takes place in it as it begins to dry. The water at greater distances from the drain will find its way into them through these cracks or fissures; and then the process of drying goes on till the entire of the water contained in the soil shall have escaped. It is manifest, from what must necessarily take place in the subsoil subsequent to the removal of the water, that the rain falling on the surface must soon find its way down through the fissures of the subsoil, from which it escapes into the drains, as before, and through which it is ultimately conveyed to the natural discharging channel of the district. The underground operations of nature, thus described, may be witnessed on the surface, in clayey or peaty soils, which absorb and retain three times as much water as some sandy soils do. In spring, when such clayey or peaty soils become dry, they shrink in considerably, separating into hard masses, with large fissures between. Upon

this principle, the degree of contraction, diminution in bulk, and hardness in every soil, will be in proportion to the quantity of these it contains; and as most subsoils partake more or less of either of these, it follows, that draining has the effect of producing these masses of different degrees of hardness in every subsoil, except those that are sandy or gravelly. The tender roots of the growing crop cannot enter these solid masses, which also exclude the air: in dry weather, the active soil over them will be parched, and in wet weather, the rain, with all the nourishing substances it brings from the atmosphere, passes quickly through the thin stratum of active soil, and descends through the fissures, where the beneficial effects of all are partly lost. The best part of the artificial manures is also washed down through the fissures, where its beneficial influence is lost. Hence, it is evident that something more is required than thorough draining, in order to preserve to the growing crop all the nourishing qualities of the soil, atmosphere, and artificial manures. To attain this desirable object, subsoil ploughing has been found eminently successful.

The process of subsoil ploughing is very simple. A common plough, drawn by two horses, goes before the subsoil plough, removing a strip of the active soil, and laying it to one side; the subsoil plough follows in the open furrow, penetrating through and breaking the subsoil, without removing it to the right or left. The common plough again throws another strip of the active soil over the subsoiled furrows, the subsoil plough following, as before, softening and breaking up the subsoil to such a depth as may be thought necessary. In this manner the process goes on till the entire field is gone over. By this process the active soil is left on the top, and the