MATERIALS FOR DRAINS. 171 



laying the tiles. As the tiles are laid they are covered 

 with sufficient earth to protect them from injury by any 

 accident, and the filling in of the ditches may be finished 

 after the tiles are all laid. 



One inch tiles are sufficiently large for the lateral drains, 

 unless these are longer than. 500 or 600 feet, when the low- 

 er part should be 1 i inch. Drain tiles carry 4 times as 

 much water for twice the diameter; (increasing in capacity 

 as the square of the diameter, or the diameter multiplied 

 by itself.) Thus a 2 inch tile carries as much water as 4 one 

 inch tiles; 9 times as much for 3 times the diameter; 16 

 times as much for 4 times the diameter and so on, thus in- 

 creasing as the square of the diameter. -If 16 one inch tiles 

 are discharging to their full capacity, a 4 inch tile will 

 take all the water ; but as an excess of water stops the flow 

 and backs up the water, and favors the deposit of sediment, 

 it is advisable to have the main and outlet pipes larger than 

 is absolutely necessary so as to secure as rapid a discharge 

 of the water as possible. 



Stones make an excellent and permanent drain when 

 well laid. A clear channel is made by placing long nar- 

 row stones along each side of the ditch and covering these 

 with flat ones placed crosswise. These are covered with 

 round stones packed closely, and these again with small 

 and flat stone over which earth is thrown. This method 

 is economical when the land is stony, and gets rid of stone 

 cheaply and permanently. 



Gravel, may be used for making drains where it is 

 abundant and near at hand. The drains in this case are 

 made 6 inches wide at the bottom and are filled in with 

 clean gravel 18 inches deep; over this the earth is filled in. 

 The gravel should be clean and free from clay or sand 

 which would be washed into the bottom of the drains and 

 choke the flow of water. 



Wooden pipes may be used in draining marshes and quick- 

 sand bottoms, with good effect. These are best made of 

 hemlock boards which are the most durable under water 

 6 inches wide, and nailed together in the shape of a V ; 



