GROUND OPEEATIONS. 



239 



plummet or spirit-level teads or stands true, tlie fall 

 will be regular from one end of the drain to the 

 other. As it is exceedingly awkward to get any level 

 into the bottom of a drain, or to use it when there, 

 boining-rods may be used, and the straight- edged 

 level placed on the top of their cross-bars, with the 

 addition suggested ; the thickness of the splice may 

 be so adjusted as to give a regular fall throughout 

 any length of diain. The fall should invariably be 

 regular throughout, with this exception, that the 

 drains should discharge themselves into the main or 

 outlets at a sharper fall, and consequently with 

 greater speed, than they rim through any other 

 portion of their course. This simple expedient is 

 one of the surest antidotes to silting up and blocking 

 the mouth of the drains, secondary or main. 



Sizes of Drains. — The efficiency of drains 

 IS not seldom in the inverse ratio of their area. 

 The smaller the more efficient, when well made, and 

 possibly the less danger of silting up ; and drains are 

 only safe against blocks when fairly at work. It has 

 also been found on calculation that inch drains are 

 of sufficient area to cope successfully with any amount 

 of rainfall that we have to deal with in our climate. 

 It is very seldom that more than an inch of rain falls 

 in twenty-four hours. This amounts to something 

 like one hundred tons to the acre, and inch drains 

 could easily discharge this in eighteen or twenty-four 

 hours. It has been calculated an inch drain can 

 readily discharge half a ton of "water per hour. As 

 there are twenty-four hours in a day, and generally 

 several drains in an acre, it is easy to see that even 

 the smaller drains are not likely to be over-freighted 

 for any length of time with an excess of water. Any 

 small aperture can pass an enoraious amount of 

 water through it in a given time, especially when, as 

 in the case of full drains, the current is strong and 

 the motion perpetual so long as there is any water to 

 move. 



However, in gardens^ in which the permanent 

 crops forbid a repetition of drainage, it is well to 

 use tiles of two or even more inches for the drains. 

 Three-inch mains, and an inch and a half or two 

 inches for feeders are, however, amply sufficient. 

 The tiles may be either round (Fig. 15), horse-shoe 

 (Fig. 16), or elliptical, the form matters little. Open 

 horse-shoe tiles, laid on a movable sole, are also 

 used at times (Fig. 16). These are in nowise better 

 than the horse-shoe tile made in the usual way. 

 Superior tiles, especially those used in the mains, 

 are also generally made with sockets ; that is, the 

 one end of each pair of tiles slips into the 

 other (Fig. 17). These, however, cost more, and 

 are not much believed in by practical drainers. 

 AVhere the subsoil is stiff, and the point of union 



between the pairs of tiles is clayed over, the drain 

 is moulded into a union throughout, and seldom or 

 never gets blocked up. 



Several Tiles in One Drain.— The intro- 

 duction of two or more small tiles to take the place 

 of one larger tile is a very old method of draining. 

 Illustrations of two such drains are given. There is 

 no objection to the piling together of tiles in tLe 

 bottom of drains, only the expense. In Fig. 18, Xo. I 

 shows a drain cut out with an elbow, with one tile on 

 the bottom. No. 2, a drain bottomed with the horse - 



Fig. 15.— Common Eound Drain-tile, without Socket. 



shoe tiles, the bottom one inverted ; and No. 3 is 

 finished with three tiles of the same shape, the upper 

 one resting on the two lower. The last two drains 

 are made somewhat wider to receive these additional 

 tiles. 



Stone drains again, as Nos. 4, 5, 6, 7 (Figs. 18, 19), 

 are made of different forms as weU as sizes. The 

 Box drain, No. 4, derives its name from its form. 



Fig. 16. — Horse-shoe Drain-tile, with Movable Sole. 



Where sand, flint, or other stones, easily split or 

 broken into slabs, abound, there is no drain more 

 easily made, few more efficient. The Angle stone 

 drain. No. 5, consists of a single or several large 

 stones for a base, on which two pieces are set to form 

 the point of a triangle in the centre of the drain. The 

 vacant spaces on either side of the angle are filled 



Fig. 17.— Common Eound Drain-tile, with. Socket. 



full of rubble or rough stone, and these are disposed 

 in the best possible position for the rapid discharge 

 of water into the drain. Fig. 19 shows the more 

 common rubble or flint drains, filled up to different 

 depths. This description of drain should average a 

 foot in depth, and from six to nine inches in width. 



It is needful to make stone di-ains of larger area 

 than those of tiles, as the danger of silting up 

 increases in the direct ratio of the amount of such 

 drainage material as broken stones, and thus the 



