176 
E. MAWLEY-PERCOLATION OF RAIN 
practicable in the same order they occupied in the spots from which 
they had been dug. In order to prevent cracks forming in dry 
weather, the surface of the soil in each gauge is hoed regularly 
once a week to the depth of about an inch. This also serves to keep 
down weeds. 
Although the gauges were filled during the autumn of 1885, 
nearly 2 i years were allowed to elapse before any regular measure¬ 
ments were made, as it was considered advisable to allow the soils 
sufficient time to settle down and become fairly consolidated. Of 
course in such confined spaces there is little hope of their ever 
becoming anything like as firm as in their natural state. 
From Table I it will be seen that the total rainfall for the 
whole period over which these observations extend (April, 1888,, 
to March, 1891) was 73-J- inches. Of this amount 47 inches, or 
about 63-9 per cent., passed through the 2\ feet of comparatively 
heavy soil, and 43-|- inches, or 59-2 per cent., through the same 
depth of lighter soil; so that the drainage through the more 
retentive soil exceeded that through the lighter soil by altogether 
3£ inches, or 7i per cent. It therefore follows that the evapora¬ 
tion from the surface of the. heavy soil must have fallen short of that 
from the surface of the light soil by precisely the same amount, 
viz. 3£ inches. 
We come next to Table II, which gives the rainfall, percolation, 
and evaporation for the summer halves of three drainage years. 
It may be here explained that what is termed a “ drainage year ” 
begins with October and ends with the following September, and 
that the summer half of it commences with April and ends with 
September. Taking the totals for these three summers it will be found 
that the heavy-soil drainage amounted to 45 per cent, of the rain¬ 
fall, whereas that through the light soil was only 36’9 per cent., 
or 8T per cent. less. It will also be noticed that the total 
evaporation from the light soil exceeded the drainage through it 
by about 10 inches, whereas from the heavier soil it was only 
4 inches in excess of the drainage. 
In Table III will be found similar data for the winter halves of 
three drainage years beginning in each case with October and 
ending with the following March. This is the period when there 
is least evaporation, and therefore when the drainage is at its 
maximum. Indeed, it might almost be said that our underground 
water-supply would never be replenished at all were it not for 
these winter rains; for in Nature it is seldom that the rain which 
falls during the rest of the year has any chance of finding its way 
permanently into the ground. The difference between the 
quantities passing through the two soils during this period, owing 
to the small amounts evaporated from their surfaces, will be seen 
to have been but slight. In fact the drainage through the heavier 
soil was 85*4 per cent., and that through the lighter soil 84‘6 per 
cent, of the aggregate rainfall, or a difference in favour of the 
heavier soil of barely 1 per cent. The differences between the 
quantities evaporated consequently also come out small. 
