THE FARMER'S MAGAZINE, 



379 



being at a considerably greater depth, and In their dis- 

 tance apart being in some measure, under circumstances 

 to be explained hereafter, regulated by the depth. The 

 depth of drains under Parkes' mode being much greater 

 than that in the Deanston system, the former method 

 will intersect a greater number of under-ground water- 

 feeders, and thereby prevent their outburst at the sur- 

 face, than the latter, and so, in some measure, perform 

 the functions of Elkington's system of draining. 



The first object, in draining by the system now being 

 treated of, is to determine upon a proper outfall of 

 drainage water from the covered drains into some trunk 

 drainage or natural watercourse, which should be pre- 

 pared or put into a state of efficiency, to convey the 

 water from the main drains without impediment, or with 

 as little obstruction as circumstances will admit of. 

 The next matter to be attended to, is to trace a main or 

 receiving drain from the outfall at the trunk-drain along 

 the lowest level of the pround to be drained. 



Although a very trifling fall will give motion to 

 water, yet, whenever it can be avoided, no drain should 

 have a less descent than 10 feet per mile, or \h inch to 

 a statute chain of 66 feet in length. A greater fall, 

 however, than 8 inches to a chaiti in length is not to be 

 desired. Whenever the descent of ground in which a 

 main drain has to be carried exceeds 10 or 12 inches 

 to a chain, it will be preferable to lay out the drain in 

 lengths or reaches, at uniform falls of less than 8 inches 

 to a chain, and connect such lengths by inclined planes 

 ^letting down the water from the lower end of the 

 higher lensih to the higher end of the lower length — 

 than to maintain one uniform descent with so great a 

 fall. 



When the ground is flat, and the subsoil of a uniform 

 nature, it matters not in what direction the drains run, 

 provided the main or receiving drain be along tlie lowest 

 level of the ground to be drained. When want of suffi- 

 cient fall may necessitate the bottom of a main drain at 

 its outfall being on a level, or nearly so, with the bed of 

 an open watercourse into which such main drain is dis- 

 charged, it will be advisable to have, here and there, 

 settlers of brick-work in the course of the drain, with 

 their bottoms below the bottom of the drain, and carried 

 up to the surface, where, having lids, the drain may be 

 examined at different points in its course, and any solid 

 matter that may have entered the drain removed. One 

 of such settlers should be near the outfall of the drain. 



On sloping ground, the direction of the collecting 

 drains should always be in the direction of the slope, 

 and not across it; as by the former-mentioned direction 

 every stratum in the subsoil to the depth of the drain is 

 certain to be intersected, by which the water from the 

 feeders in the subsoil will be intercepted and carried off 

 before coming to the surface ; whereas, by the latter- 

 mentioned direction, the drains will be as likely to miss 

 as to intercept the water-feeders in the subsoil, and will, 

 therefore, be uncertain in efficiency. It very seldom 

 occurs, however, that ground slopes entirely in one 

 direction. When the surface of the ground slopes in 

 two directions, the most proper direction in which the 

 drains should be laid off is in an obli(iue direction be- 

 tween the two declivities, nearer of course to that of the 

 greater, by which the direction of the water at its dis- 

 charge into the main drains will be incline to the direc- 

 tion of the currents thereof, and so offer the least inter- 

 ruption to its free discharge. 



The foregoing diagram shows a convenient mode of 

 laying off collecting drains. Take any point, c being an 

 intersection of the direction of two given slopes of sur- 

 face, c A, c B, and from c to a and u measure any two 

 lengths proportionate to the rates of fall of the said 

 slopes. Measure in a direct line the distance between 

 A and B, and set off a e, half the distance a b ; then e 

 will be a point in the proper direction of the collecting 



drains from c. Let the line c e be extended towards d. 

 Trace lines f g and h i square to c d, and upon such 

 square lines set off, at any required distance apart, 

 parallel lines a, a, a, a, a, a, a, a, for the direction of 

 the collecting drains required. 



The most convenient instrument for setting out the 

 lines F G and h i square to c d is a reflecting square, 

 which may be carried in the waistcoat pocket. 



