48 The Drainage of Fens and Low Lands, 



bottom of the trench is by this means at once detected. The 

 use of these rods is acquired with very little experience, and 

 levels can be ascertained with quite sufficient accuracy for 

 all practical purposes. 



If it is desired to find the inclination or fall of the ground, 

 all that is necessary is to fix two pegs about lo feet apart 

 from each other, making them level with the aid of a 

 straight-edge and spirit-level, or with a carpenter's level and 

 plumb-bob ; and then holding the two boning rods as before 

 on these pegs, the third rod with the sliding leg is to be 

 held at the lower end of the trench, or wherever else it is 

 required to level to, and then sliding out the leg until the 

 tops of the three rods are in a line ; the distance the leg has 

 to be drawn out gives the fall. 



Pipes. — After trying various sizes and shapes for the pipes, 

 opinion is now universally in favour of cylindrical tubes, 2 

 inches in diameter and i foot long, for the small or feed 

 drains, and from 3 inches to 4 inches in diameter for the 

 mains. Some tile-burners manufacture a circular pipe, 

 having a flat bottom ; if they could ensure that these would 

 burn without the least twisting, there would perhaps then be 

 a slight advantage in their having a better bearing on the 

 bottom of the trench ; but as this is never the case, the flat 

 bottom is worse than useless, in rendering the pipes heavy 

 and cumbersome. The author has repeatedly watched men 

 laying these pipes, and half were not laid with the fiat part 

 downwards, the reason given being that the men could not 

 make the ends fit when so laid. The circular pipes are less 

 liable to warp and bend in the burning, having the same 

 thickness of material on every side, and are therefore easier 

 and better to lay. Collars are occasionally used, but are 

 quite unnecessary, except in very rotten ground, when they 

 are useful in assisting to Jkeep the ends of the pipes from 

 dropping away from one another. In such*^round, in order 

 to lay the drains effectually, the expedient should be resorted 



