TILE AND PIPE DRAINING. 117 



pipe drains of only one inch bore are used, they do not admit of 

 the entrance of vermin. On Mr. Smith s plan, however, the 

 main drains are covered as well as the side drains, and the en 

 trance or outlet of the main drain may be protected by an iron 

 grating, or a foot or two of broken stone laid down at the end. 

 It is advised that the main drain should be sunk six inches 

 lower than the side drains ; but where pipes are used, the side 

 drains may enter directly into the main drains, the pipes being 

 made with a hole in the side, for this express purpose. It has 

 been found quite effectual, in some cases, to lay two pipes for a 

 main drain, side by side ; but it would seem most desirable to 

 have a pipe of a large bore for the main drain, and of a sufficient 

 size to receive all the water which should be emptied into it 

 from the side drains. Such pipes, at Mr. Stirling s, near Fal- 

 kirk, were of a very large bore, and made in three parts, so as 

 exactly to fit each other when brought together. The advantage 

 of a concave or circular bottom for the water to flow in. in pref 

 erence to a flat sole, must be obvious at first thought. Tiles 

 have been constructed with a circular bottom, like a horse-shoe 

 set upon its front edge, and a flat cover to rest upon it ; but 1 

 can see no advantage which this has over a pipe ; unless it might 

 be that, by the removal of the cover, the seat of any obstruction 

 might be ascertained without lifting the whole. 



It is often found necessary to make what are called siibmain 

 drains, which of course communicate with the main drain. This 

 must depend upon the nature of the ground, and where these 

 submains are made on the side of a hill, they are best made ob 

 liquely, crossing the small drains diagonally, and thus giving an 

 impulse to the water received into them. It is advised, in all 

 cases, to make the parallel drains, which connect with the main 

 or the submain, straight, whether running on level land, or on a 

 side hill and it is deemed best that no small or parallel drain 

 should ever exceed two hundred yards in length, without empty 

 ing into a main or a submain drain. The distance at which the 

 drains should be placed apart may vary with the nature of the 

 soil, from a rod to forty or sixty feet. It may be interesting to 

 know the length of drainage, or of pipe, which may be required 

 in an acre, at the different distances which are customarily 

 adopted. I subjoin, therefore, the following table : 



