153 



been correctly laid, none of the pests of the farm can enter between 

 the joints. 



The main drains should le constructed in the lowest parts of the 

 field, and a proper outlet for carrying away the water provided ; without 

 this, draining cannot be effected. A calculation should be made of the 

 quantity of water likely to flow into the main drains and tiles sufficient 

 to carry it away, should be provided. Tile drains should not be con- 

 structed so as to discharge their water into stone drains, for they are 

 apt to carry sand and sediment sufficient to choke the stone drains. 

 Drains made of stones may be permitted to discharge into tile drains, 

 for the water in them is generally well filtered and free from sediment. 



The following figures represent etone and tile drains : 



16 JNOUBS 



12 IVCHBS 



IS IHCHIS 



4khl^ 



SmCHES 



4/,»C,« 



Mr. Parks the talented engineer of the Royal Agricultural Society 

 of England, recommends that drains should be made four feet deep 

 and forty feet asunder. He says he finds that deep drains run sooner 

 after rain than shallow ones. A circumstance which is thus accounted 

 for : when water falls on the surface it sinks directly into the soil, and 

 continues to descend until it meets an impervious subsoil, here it stops 

 and according as it receives supplies from above, rises towards the sur- 

 face. The deeper the drain is, the sooner the rising water will reach it, 

 and the shallower the drain, the longer will the water be in coming up 

 to it. It will be seen by this that the water enters at the bottom and 

 sides instead of at the top of the drain. The deeper the drain is, the 

 greater will be the pressure of the water from the surface, and conse- 

 quently the more rapidly will it run. 



The followinc' ficrure will serve to illustrate this law of fluids: 



20 



