194 NOTES ON THE SEASONS OF 1893.
surface became much drier and hotter than usual. On very fleet
springs this had a decided effect. In my own neighbourhood
(Felstead) our springs circulate at a depth of about twenty to forty
feet, and as the quantity of water in the river, which might be
described as wholly derived from the springs, remained constant
(with one exception, to be presently noticed), we could not observe
that the springs were affected. The time of greatest scarcity of
river water is usually October and November, but this year no
scarcity has been noticed. We therefore conclude that the present
supply is due to rains preceding the drought, that is, not later than
February, and we also infer that the summer rains do not materially
affect these deeply-seated springs.
The one exception to the normal flow of the river was due to
the hot days of August. I am indebted to the miller at Felstead
for the following observation : Immediately upon the advent of those
few hot days there was a marked diminution in the river supply,
the "head" being exhausted in about three-quarters of its ordinary
time ; but on the arrival of cooler weather the full supply again
returned, and this without any rain having fallen, so far as is known,
within the area of drainage. This phenomenon could only have
been due to the excessive evaporation caused by the sun. It is
certainly very unusual to have the opportunity afforded in Essex of
getting a direct measure of the influence of the sun's rays in causing
evaporation. It may be here obtained to a near approximation,
because the daily quantity of water passing the mill is well known,
and a loss of a quarter of that quantity represents the total loss on
the whole surface of the stream up to its source. This bearing but
a very small proportion to the drainage area, it becomes apparent
that the force of the sun's rays in causing evaporation must be very
great indeed; and it moreover shows that the quantity of water
discharged by the leaves of plants must be considerable in volume.
This great volume of water (escaping as vapour) and the flow of
the river throughout the summer is the measure of the demand, less
a small portion of the rainfall, which has been made upon the spring
since last February. We are not concerned to go further into the
subject here; we have only noted the good opportunity afforded by
the season to deal with some approximation with that subject.
It remains to consider whether any permanent effects may result
from this extraordinary summer.
Our experience of the past leads us to suppose that there will be