108 DIRECTION OF THE DRAINS. 



the first object must be to cut off the flow of water 

 upon or near the surface. An open ditch across 

 the top would most certainly effect this purpose, 

 and it may be doubtful whether any other drain 

 would be sufficient. This would depend upon the 

 quantity of water flowing down ; if it be very great 

 at times, a part of it would be likely to flow across 

 the top of an under drain, from not having time to 

 percolate downward into it. 



" In all cases it is advised, when the work stops 

 upon a slope, to introduce a cross-drain connecting 

 the tops of all the minors. This is called a header. 

 Its object is to cut off" all the water that may be 

 passing along in the subsoil down the slope, and 

 which would otherwise be likely to pass downward 

 between the system of drains to a considerable depth 

 before finding them." 



In deciding the direction of the drains we must 

 be careful to ascertain the source from which the 

 water proceeds. If it arises from springs, the aim 

 must be to direct thera so as to cut off the fountain, 

 — and at this point they must be frequent, — while 

 below it may not be necessary to place them at less 

 than double the distance. If the surplus water is 

 rolled down from higher land, the direction must 

 be such as to head off and carry it away : the size 

 of the pipes and frequency of the drains must cor- 

 respond with the amount of water to be disposed 

 of "When we have only to contend with the mois- 



