446 Farm Mechanics. 



ter at any season of the year rises to within three or four 

 feet of the surface there the road-bed should be drained. 

 In humid climates provisions should be made to surface 

 drain every road, 



"647. The Relation of Water to Roads. When a soil is 

 completely filled with water the individual soil grains are 

 invested by water and tend to float in it so that there is the 

 greatest freedom of motion of the particles* On the other 

 hand let all water be removed from the soil and the ground, 

 while hard, easily frets into fine, loose, separate dust 

 particles, which not only increase the draft but are easily 

 drifted away by the wind, thus injuring the road much 

 as it would be were the top washed away by running 

 water. 



There is a medium condition or amount of water in the 

 soil which gives it power to withstand the eroding tendency 

 of the tramp of the horses' feet and the rolling of the 

 wheels. When sand is just wet enough its surface is hard 

 and will carry a heavy load, the grains being bound to- 

 gether by the surface tension of the water films. So, too, 

 with the clay roads and those of the best of loam^ the right 

 amount of water always present, so as to keep the sur- 

 face damp and dark without making them soft, greatly 

 improves the quality and lengthens their life. So valua- 

 ble is the right amount of water on earth roads that sprink- 

 ling them in arid and semi-arid climates and in dry times 

 in humid climates, is one of the most effective means of 

 maintenance. 



548. Depth of Under Drainage. Where under drainage is 

 needed the drain should not be less than three to four feet 

 deep, and this is especially true if heavy traffic is to be 

 maintained over it. 



No one thinks of walking on the yielding surface of the 

 water of a lake or stream, but let it be covered with a suffi- 

 ciently thick layer of ice and it then makes the best kind of 

 a road-bed. The drained ground beneath the road surface 



