GROUND OPEEATIONS. 



239 



plummet or spirit-lOTel lieads or stands true, the 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 drain. 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 run through any other 

 jiortion of their course. This simple expedient is 

 one of the surest antidotes to silting up and blocking 

 ±he 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 

 j)0ssibly 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 

 iours. 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 

 :8mall aperture can pass an enormous amount of 

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

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

 ■the motion perpetual so long as there is any water to 

 jnove. 



However, in gardens in which the permanent 

 /;rops 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 tUes, 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. 

 Where the subsoil is stiff, and the point of union 



between the pairs of tUes is clayed over, the drain 

 is moulded into a union throughout, and seldom or 

 never gets blocked up. i 



Several Tiles ia One Drain. — The intro- 

 duction of two or more small tUes 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 piUng together of tiles in the 

 bottom of drains, only the expense. In Fig. 18, No. 1 

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

 the bottom. No. 2, a di-ain bottomed with the horse- 



rig. 15.— Commoii Round 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 well as sizes. The 

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



Fig. 16.— Horse-slioe 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 



rig. 17. — Common Botmd Drain-tile, with Socket. 



f uU 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 drains 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 



