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line of steepest descent were, however, so clear, and drains laid on that line were so universally successful in practice, that it was long ago adopted by all,-save those novices who preferred to gain their education in draining in the expensive school of their own experience.

The more important reasons why this direction is the best are the following: First, it is the quickest way to get the water off. Its natural tendency is to run straight down the hill, and nothing is gained by diverting it from this course. Second, if the drain runs obliquely down the hill, the water will be likely to run out at the joints of the tile and wet the ground below it; even if it do not, mainly, run past the drain from above into the land be low, instead of being forced into the tile. Third, a drain lying obliquely across a hillside will not be able to draw the water from below up the hill toward it, and the water of nearly the whole interval will have to seek its outlet through the drain below it. Fourth, drains running directly down the hill will tap any porous water bearing strata, which may crop out, at regular intervals, and will thus prevent the spewing out of the water at the surface, as it might do if only oblique drains ran for a long distance just above or just below them. Very steep, and very springy hill sides, sometimes require very frequent drains to catch the water which has a tendency to flow to the surface; this, however, rarely occurs.

In laying out a plan for draining land of a broken sur face, which inclines in different directions, it is impossible to make the drains follow the line of steepest descent, and at the same time to have them all parallel, and at uniform distances. In all such cases a compromise must be made between the two requirements. The more nearly the parallel arrangement can be preserved, the less costly will the work be, while the more nearly we follow the steepest slope of the ground, the more efficient will each drain be. No rule for this adjustment can be given, but a careful

study of the plan of the ground, and of its contour lines, will aid in its determination. On all irregular ground it requires great skill to secure the greatest efficiency consis tent with economy.

The fall required in well made tile drains is very much ess than would be supposed, by an inexperienced person, to be necessary. Wherever practicable, without too great cost, it is desirable to have a fall of one foot in one hundred feet, but more than this in ordinary work is not especially to be sought, although there is, of course, no objection to very much greater inclination.

One half of that amount of fall, or six inches in one hundred feet, is quite sufficient, if the execution of the work is carefully attended to.

The least rate of fall which it is prudent to give to a drain, in using ordinary tiles, is 2.5 in 1,000, or three inches in one hundred feet, and even this requires very careful work.* A fall of six inches in one hundred feet is recommended whenever it can be easily obtained-not as being more effective, but as requiring less precision, and conse. quently less expense.

Kinds and Sizes of Tiles.-Agricultural drain-tiles are made of clay similar to that which is used for brick. When burned, they are from twelve inches to fourteen inches long, with an interior diameter of from one to eight inches, and with a thickness of wall, (depending on the strength of the clay, and the size of the bore,) of from one-quarter of an inch to more than an inch. They are porous, to the extent of absorbing a certain amount of water, but their porosity has nothing to do with their use for drainage, for this purpose they might as well be of glass. The water enters them, not through their walls,

* Some of the drains in the Central Park have a fall of only 1 in 1,000, and they work perfectly; but they are large mains, laid with an amount of care, and with certain costly precautions, (including precisely graded wooden floors,) which could hardly be expected in private work

but at their joints, which cannot be made so tight that they will not admit the very small amount of water that will need to enter at each space. Gisborne says:

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"If an acre of land be intersected with parallel drains "twelve yards apart, and if on that acre should fall the "very unusual quantity of one inch of rain in twelve "hours, in order that every drop of this rain may be dis"charged by the drains in forty-eight hours from the commencement of the rain—(and in a less period that quan"tity neither will, not is it desirable that it should, filter "through an agricultural soil)—the interval between two "pipes will be called upon to pass two-thirds of a tablespoonful of water per minute, and no more. Inch pipes, "lying at a small inclination, and running only half-full, "will discharge more than double this quantity of water "in forty-eight hours."

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Tiles may be made of any desired form of section,—the usual forms are the "horse-shoe," the "sole," the “double-sole," and the "round." The latter may be used with collars, and they constitute the "pipes and collars,” frequently referred to in English books on drainage.

Horse-shoe tiles, Fig. 13, are condemned by all modern engineers. Mr. Gisborne disposes of them by an argument of some length, the quotation of which in these pages is probably advisable, because they form so much better conduits than stones, and to that extent have been so successfully employed, that they are still largely used in this country by "amateurs."

Fig. 13.-HORSE-SHOE TILE.

"We shall shock some and surprise many of our readers, when we state confidently that, in average soils, and, still more, in those which are inclined to be tender, horse shoe tiles form the weakest and most failing conduit which has ever been used for a deep drain. It is so, however; and a little thought, even if we had no experience, will tell us that it must be so. A doggrel song, quite destitute of humor, informs Ls that tiles of this sort were used in 1760 at Grandesburg Hall, in Suf

area.

folk, by Mr. Charles Lawrence, the owner of the estate. The earliest of which we had experience were of large area and of weak form. Constant failures resulted from their use, and the cause was investigated; many of the tiles were found to be choked up with clay, and many to be broken longitudinally through the crown. For the first evil, two remedies were adopted; a sole of slate, of wood, or of its own material, was sometimes placed under the tile, but the more usual practice was to form them with club-feet. To meet the case of longitudinal fracture, the tiles were reduced in size, and very much thickened in proportion to their The first of these remedies was founded on an entirely mistaken, and the second on no conception at all of the cause of the evil to which they were respectively applied. The idea was, that this tile, standing on narrow feet, and pressed by the weight of the refilled soil, sank into the floor of the drain; whereas, in fact, the floor of the drain rose into the . tile. Any one at all conversant with collieries is aware that when a strait work (which is a small subterranean tunnel six feet high and four feet wide or thereabouts) is driven in coal, the rising of the floor is a more usual and far more inconvenient occurrence than the falling of the roof: the weight of the two sides squeezes up the floor. We have seen it formed into a very decided arch without fracture. Exactly a similar operation takes place in the drain. No one had till recently dreamed of orming a tile drain, the bottom of which a man was not to approach personally within twenty inches or two feet. To no one had it then occurred that width at the bottom of the drain was a great evil. For the convenience of the operator the drain was formed with nearly perpendicular sides, of a width in which he could stand and work conveniently, shovel the bottom level with his ordinary spade, and lay the tiles by his hand; the result was a drain with nearly perpendicular sides, and a wide bottom. No sort of clay, particularly when softened by water standing on it or running over it, could fail to rise under such circumstances; and the deeper the drain the greater the pressure and the more certain the rising. A horse-shoe tile, which may be a tolerably secure conduit in a drain of two feet, in one of four feet becomes an almost certain failure. As to the longitudinal fracture-not only is the tile subject to be broken by one of those slips which are so troublesome in deep draining, and to which the lightly-filled material, even when the drain is completed, offers an imperfect resistance, but the constant pressure together of the sides, even when it does not produce a fracture of the soil, catches hold of the feet of the tile, and breaks it through the crown. Consider the case of a drain formed in clay when dry, the conduit a horse-shoe tile. When the clay expands with moisture, it necessarily presses on the tile and breaks it through the crown, its weakest part. When the Regent's

The tile has been said, by great authorities, to be broken by contraction, under some idea that the clay envelops the tile and presses it when it contracts. That is nonsense. The contraction would liberate the tile. Drive a stake into wet clay; and when the clay is dry, observe whether it clasps the stake tighter or has released it, and you will no longer have any doubt whether expansion or cca traction breaks the tile. Shrink is a better word than contract.

Park was first drained, large conduits were in fashion, and they were made circular by placing one horse-shoe tile upon another. It would be difficult to invent a weaker conduit. On re-drainage, innumerable instances were found in which the upper tile was broken through the crown, and had dropped into the lower. Next came the form, tile and sole in one, and much reduced in size-a great advance; and when some skillful operator had laid this tile bottom upwards we were evidently on the eve of pipes. For the tile a round pipe moulded with a flat-bottomed solid sole is now generally substituted, and is an improvement; but is not equal to pipes and collars, nor generally cheaper than they are."

One chief objection to the Sole-tiles is, that, in the drying which they undergo, preparatory to the burning, the upper side is contracted, by the more rapid drying, and they often require to be trimmed off with a hatchet before

Fig. 14.-SOLE TILE. they will form even tolerable joints; another is, that they cannot be laid with collars, which form a joint so perfect and so secure, that their use, in the smaller drains, should be considered indispensable.

The double-sole tiles, which can be laid either side up give a much better joint,

but they are so heavy as to make the cost of transportation considerably greater.

Fig. 15.-DOUBLE-SOLE TILE.

They are also open to the grave objection that they cannot be fitted with collars.

Experience, in both public and private works in this country, and the cumulative testimony of English and French engineers, have demonstrated that the only tile which it is economical to use, is the best that can be found, and that the best,-much the best-thus far invented, is the "pipe, or round tile, and collar," and these are unhesitatingly recommended for use in all cases. Round tiles of small sizes should not be laid without collars, as the ability to use these constitutes their chief advantage; holding them perfectly in place, preventing the rattling

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