276 0)1 the Rain and Drainage - Waters at Rothamsted. 
smaller proportion of soluble salts than is found in the true 
discharge from the soil. This difference in composition has 
been very frequently exemplified in the analyses of the Rotham- 
sted drainage-waters, and has enabled us to trace the distinction 
between these two classes of drainage-water. 
When rain has ceased, and a period of dry weather occurs, 
water will begin to evaporate from the surface of the soil ; the 
water in the subsoil will be gradually drawn up by capillary 
attraction as the surface dries, and be itself in turn evaporated. 
The depth to which the subsoil will be dried by this loss of 
Avater through capillary attraction will depend on the me- 
chanical texture of the soil ; the depth will be greater in the 
case of a loam or clay than in the case of a soil of more open 
texture, the height to which water can be raised by capillary 
attraction being in proportion to the fineness of the spaces 
through which it passes. 
It is obvious that in the case of a soil like that at Rotham- 
sted, having a subsoil of clay not many feet in depth, resting 
upon chalk tending constantly to drain it, the conditions affect- 
ing the discharge of water from the land within a limited 
depth from the surface will be in the main very different from 
those occurring in a soil having a considerable depth of re- 
tentive clay. In the former case, the discharge within, or not 
far below, the usual limits of artificial drainage, will in a much 
greater degree depend on the direct downward passage of water, 
and much less on the raising of the point of saturation from 
below. It is further obvious that in a soil so naturally drained, 
the greater the amount of rainfall in a given season, the greater 
will be the depth to which a given amount of water will pass, 
while in a season of smaller rainfall the depth of penetration will 
be less. We should expect, therefore, that in a dry season the 
percolation would be greater through 20 than through 40, and 
greater through 40 than through 60 inches of soil. In a wet 
season, on the other hand, the amount of percolation would 
be relatively increased at the lower depths, and would tend 
towards equality. This would be the case if no interfering 
circumstances were imported into the question by the fact of 
absolutely cutting off the blocks of soil at different depths, 
thereby preventing the possibility of capillary attraction acting 
and water returning upwards from below the point at which 
the cutting off had taken place. Another consequence of this 
cutting off would be to cause a more complete drying of the soil 
20 inches deep during dry periods than of that to a correspond- 
ing depth in the deeper gauges. The shallower soil would 
therefore require more water to saturate it to the same depth 
when subsequent rains came, and hence the amount of water 
