The Mean Monthly Amount of Evaporation and Rain at Milwaukee, WI over a 5 Year Period

EVAPORATION AND RAIN.—The yearly
amount of evaporation, at any place is
a very important element in its meteor-
ological characteristics, and one but
seldom ascertained by direct observa-
tion. Exposing a basin of water in the
open air, will give an approximate re-
sult, and may be measured very accu-
ately by means of a micrometer screw,
turned down every morning until its
point touches the surface. The follow-
ing table shows the mean monthly re-
sult of observations so made at Milwau-
kee for over five years. Ice prevented
observations from December to March,
and for these months I interpolate
what must have been about the amount,
judging from the curve yielded by the
others. A column is added showing
the average amount of rain and melted
snow during the same time.

[Data Table of Evaporation and Rain Per Month]

This table, it will be seen, brings out
the important fact that here, in Mil-
waukee on the west shore of Lake
Michigan, the annual amount of eva-
poration exceeds that of the rain fall
six and three-tenths inches, or in the
proportion of twelve to ten. Hence if
that lake received no supply of water
except what falls directly upon it, in
the form of rain, snow, and hail, its
surface would recede at the rate of six
and three-tenths inches annually.

The following table shows the amount
of rain and melted snow for 1866, and
also the mean quantity for 23 years :

[Rain and Melted Snow Data Table as described above]

MILWAUKEE, Jan. 1, 1867. I. A. L.