On the Rain and Drainage - Waters at Rotliamsted. 
15 
Frankland, and our own more recent work have established, it 
will be convenient to consider (1) the variations in the com- 
position of the water due to the character and stage of the 
running; (2) the influence both of the manure and of the time 
of year. The quantity of nitrogen lost by drainage will be 
considered in the concluding section. 
Influence op the Character and Stage of the 
Running. 
We have already called attention, when speaking of the waters 
obtained from the drain-gauges, to the existence of two distinct 
kinds of drainage-water in our clay soils, one which has come 
directly from the surface through small channels in the soil, 
and the other which consists of the general discharge of the 
saturated soil ; this fact is of considerable help in explaining 
the variations in composition observed in the drainage-waters 
from the same plot. Supposing that the soluble matter in a soil 
is equally diffused throughout it, the drainage-water will be 
weaker in proportion as surface-water preponderates in the dis- 
charge. This surface-water will consist partly of the discharge 
from the upper layer of soil, and partly of little altered rain- 
water, both of these gaining access to the drains through the 
channels in the soil. This drainage from the surface will 
precede the general discharge from the mass of soil above the 
drain-pipe. The admixture of rain-water will be most con- 
siderable during heavy rain, when water accumulates on the 
surface of the land, as water will then stand over the heads of all 
existing channels. Drainage from the surface will cease soon 
after rain has stopped, the upper layer of soil being the first 
to lose its supersaturated condition. As the running at the pipe 
diminishes, the drainage-water will be successively furnished by 
lower and yet lower layers of soil, till the soil is no longer in a 
supersaturated condition above the drain-pipe. 
Under the conditions assumed, it is clear that the drainage- 
water collected at the commencement of a running will be much 
weaker than that collected at the end. A collection made during- 
a heavy, long-continued rain, when the drains are rapidly dis- 
charging, will also be much weaker than a collection made from 
the same soil when the rainfall is moderate, and the discharge 
contains a less proportion of surface-water. 
This is exactly what we observe in studying the composition 
of the drainage-waters obtained after the soluble manures have 
become diffused throughout the soil. One would perhaps have 
expected that the soluble salts (chlorides for instance) applied 
to the land as manure would appear in gradually diminishing 
