4\S 
On Draun'ii//. 
Fig. 3 shows tlio fissures, <Scc., on undulating land in the same 
manner as Fig. 2, rt a the drains, h the ridge ; the black lines are 
intended to show that the water has a much greater distance to 
flow or percolate through the fissures betore it reaches the conduit 
of the drain than upon level land. The greater the declivity of 
the land the longer will be the distance for the water to percolate 
before it reaches the conduit : deep drains, by increasing the fall 
from the ridge to the conduit, in some measure counteract and 
shorten its course. 
In Fig. 3 the water runs in an oblique, and consequently a 
longer course to the conduit of the drain than on level land, and 
if the drains are laid obliquely across the slope, as shown in 
Fig. 4, the water runs almost entirely in one direction to the 
conduit of the drain ; whereas on level or comparatively level 
land it runs each way from the centre, as shown in Fig. 2. 
On land w ith a considerable slope it is not only desirable to 
have a dry surface, but also to have as many drains as are ne- 
cessary to admit rapidly the water into the land, to prevent it 
running over the surface and carrying the soil down the slope. 
Fig. i. 
a a show the drains 30 inches deep, h h the slope, with a fall of 
I foot in 5 ; c c are horizontal lines ; rZ is a line drawn parallel 
with the slope the supposed depth of the fissures ; e the bed of 
clay below the fissures; the fissures are shown, as they run in clay 
land, by perpendicular lines : there are very fcxc which run either 
horizontal or parallel with the surface. If the water flows over 
the surface, or through the fissures to the conduit, it is evident 
that almost all the water which falls between the drains a a will 
flow from the drain marked 1 to the drain marked 2, showing 
the necessity of the drains being nearer than on level or com- 
])aratively level land, where the water, as shown in Fig. 2, flows 
equally from the ridge to the drain on each side. 
3rd. Fall required, and the necessity of levelliny hiyli-ridycd 
hinds. 
A fall less than that generally considered necessary is sufficient 
for under-drains to carry off water. One yard for every 220 is 
