326 
On the Rain and Drainage - Waters at Rothamsted. 
The figures representing the evaporation from a water surface 
Are full of interest. The average summer evaporation is 15"892 
inches ; that for winter, 4"76G inches ; the total for the year, 
^0'658 inches. The amount of variation is very considerable. 
In 1862 the annual evaporation was only 17*332 inches; in the 
hot season of 1868 it reached 26*933 inches. There are some 
.obvious reasons why the evaporation from a water surface should 
be more variable than that from a bare soil. On a water 
surface sunshine and wind must always produce their full effect, 
while on soil evaporation receives a check as soon as the surface 
ds dried. Another disturbing cause in Mr. Greaves's deter- 
minations has been variable condensation from the atmosphere, 
making the winter evaporations appear lower than they 
jeally are. 
Mr. Evans's experiments are even more striking examples of 
the disturbing action of vegetation than those of Mr. Greaves. 
The average rainfall during fifteen years has been 25"55 inches. 
Throughout this period the absence of drainage from the turfed 
soil during the summer months has been even more complete 
than in Mr. Greaves's experiments. The summer drainage 
from the turfed soil has averaged 0'35 inch, the evaporation 
12"12 inches. The winter drainage has been 5*23 inches, the 
evaporation 7"85 inches. In the whole drainage-year the ave- 
rage drainage has been 5*58 inches, the evaporation 19 97 inches. 
The summer evaporation, however, actually ranges from 7"59 to 
16'09 inches, and that of the whole year from 13*20 to 26*55 
inches. This wide range in the amount of evaporation is in 
part due to the insufficient supply of rain. The full evaporating 
power of the turf has perhaps not yet been shown, the whole of 
the rainfall having been evaporated even in the wettest summer 
^)f the fifteen years. In these experiments the distribution of 
the rain has a marked effect on the amount of drainage. Rain- 
falls not sufficiently heavy to penetrate the turf are probably 
evaporated, while those passing the turf appear, more or less, as 
.drainage. 
In the percolator filled with chalk, the average annual drainage 
has been 8*79 inches, and the evaporation 16*76 inches. In this 
-case the soil would probably be less compact, and the growth of 
grass less vigorous, than in the percolator filled with arable soil ; 
the drainage is therefore naturally larger, and the evaporation 
'2ess. 
3. — Composition of the Drainage- Water. — Before giving the 
analyses of the drainage-water obtained from the drain-gauges, 
it will be well to mention the previous manuring of the soil, and 
what is known respecting its composition. The soil forming 
the drain-gauges was previously to 1870 under ordinary arable 
