Wind 
influencing 
Bourne flows, 
Conditions 
under which 
water exists in 
the ground. 
28 
“The country people in Surrey have a saying that 
when the Croydon Bourne flow is expected in the 
Caterham Valley a south-west wind or gale favours its 
appearance, while an easterly wind drives it back. Of 
course a south-westerly wind usually brings rain, and 
an easterly wind is a dry wind producing the contrary 
effect. This explanation will probably account for the 
Bourne flow and its diminution, but there are also 
other conditions in connection with these winds that 
should receive attention and which would influence 
the flow of the Bourne.” 
Upon investigating the subject the Author found that 
the flow of the Bourne was particularly subject to varia- 
tion in flow under atmospheric pressure, and in his 
paper in 1881 gave the following explanation with 
reference to this matter. ‘‘It may be assumed in 
reference to underground water that there are three 
zones in the earth which affect the question of supply, 
the first of which is comprised in that area measured 
from the surface of the ground downwards which is 
subject to periodical wetting and partial drying. The 
depth of this zone varies no doubt every year, depend- 
ing upon the amount of rain which percolates and the 
evaporation subsequently taking place. Then there is 
a second zone in districts like the chalk formation, in 
which the water level is removed a considerable dis- 
tance from the surface, which is always charged with 
water by capillarity, and from which the water perco- 
lating from the upper zone passes on its way to the 
third or lower zone, which is occupied not only by 
water held by capillarity of the strata but by water 
which moves freely through the strata itself. This 
third or lower zone is the one which furnishes every 
year the supplies of water which are yielded by ‘the 
