22 
> 
OF А CAMBRIDESHIRE WOODLAND, 
laver. The reason for E, rising above E, for the week ending June 1 is that 
the instruments were exposed then to driving rain, and E, being more 
exposed, collected more on the evaporating surface ; the figures in this case 
probably do not represent the total evaporation possible. 
In the later parts of the year an instrument was placed on the ground near 
the permanent station. This gave very much smaller readings than any of 
the others, though its rates follow the same general curve. 
The total evaporation during the growing season works out in the following 
proportion, E; being taken as a standard :— 
E, : E, : E; : E, = 100 : 75.6 : 80:4 : 9375. 
Evaporation experiments have also been earried out in other parts of the 
wood to obtain the rates under different conditions. The effect of the closed 
canopy of shrubs is very marked; for a period of 6 days the results of 
evaporation in deep shade, and before the closing of the canopy, were :— 
A. B. 
Open Shrubs. Closed Canopy. 
Above ground Нога ...... 62 36:5 
On ground .............. ee 168 135 
The small difference on the ground is due to the fact that the absence of 
cover is partially counterbalanced by the much denser growth of the ground 
herbs. The direct effect of the shrubs is shown in the other readings, where 
the value under the closed canopy is reduced to nearly a half. 
The variations of these two sets for short periods are also interesting. 
The curves for the instruments in deep shade, for intervals of two hours, are 
practically parallel, whereas in the other pair the raised one shows sharp 
changes with changes of the climatic conditions, while that on the ground 
changes much more gradually. A noticeable feature of difference in these 
two sets is the rate at night. This falls very low upon the ground. 
This drop, however, in both instruments is greater in those in the open 
position, so much so that these give a lower value at night. The amounts for 
the night August 13-14, 1909, for a period of 16 hours, were :— 
А. В. 
Open. Shade, 
Каеда... 52 525 
On ground ......... 21 24 
In general, the curve of evaporation on the ground follows the same usual 
trend as that at higher levels, but does not show the small temporary 
changes to nearly the same extent. Evaporation follows the changes in 
