RicHarpson—Lines of Flow of Water in Saturated Soils. 311 
or less values of Lic Therefore, to make we = ‘032, the maxi- 
gok gok 
032) 0°7 
068 s ot the distance between the 
ditch centres, which is equal to 0-022 of the same. But the maximum 
rise allowed is 1 ee Therefore, the distance between the ditches 
mum height of rise must be —— 
must not exceed —— = feet = 15 yds. This is the answer required. 
It seems a likely value. But we see from fig. 2 that, if we take 
the distance between the ditches to be 15 yards, we thereby 
assume that the ditch is 2 yards broad, and that there is 3 yards’ 
depth of peat between the ditch-bottom and the clay. If these 
conditions are seriously different from the actual ones, a new figure 
must be sketched. The time taken to draw a figure increases very 
rapidly with the accuracy attempted. Those given here took me 
4 hours or so each. Half the accuracy could probably be attained 
in a quarter the time. 
Usually the lower parts of the soil are less porous. In this 
case let the paper be prepared by chequers of the proper shape 
before beginning the diagram. (See the paper on “ Freehand 
Method,” section v.) 
It may indeed be justly doubted whether the foregoing results 
will apply to the practical draining of peat-mosses as they stand. 
The hypothesis of easy vertical flow in the unsaturated upper 
layers does not seem quite satisfactory. And the effect of capil- 
larity is probably considerable (see the section thereon). But at 
any rate the present paper illustrates a method of solving the 
equations which can probably be adapted to deal with more correct 
hypotheses. 
§ 6. DETERMINATION OF THE Porosity. 
The porosity of the peat, as it lies in the bog, to the flow of 
water, can only be satisfactorily determined from a sample in 
which the original structure has been preserved, or, at least, any 
other method must be standardized against one using such samples. 
As it did not seem easy to make a water-tight joint between a 
block of peat and a vessel of glass or metal without crushing the 
softer body, I determined to make the whole apparatus of peat, 
cutting the substance into a cup-shape, putting water inside, and 
SCIENT. PROC. R.D.S,, VOL. XI., NO, XXYII. 258 
