Box 17, Folder 9: Meteorology (Milwaukee) 1859-1871

[Printed table] Rule. To find the general mean multiply the observed am for the year by its corresponding ratio.

[From Lapham Papers]

[Printed Table].

EVAPORATION AND RAIN.—The yearly amount of evaporation, at any place is a very important element in its meteorological characteristics, and one but seldom ascertained by direct observation. Exposing a basin of water in the open air, will give an approximate result, and may be measured very accuately by means of a micrometer screw, turned down every morning until its point touches the surface. The following table shows the mean monthly result of observations so made at Milwaukee 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 Milwaukee on the west shore of Lake Michigan, the annual amount of evaporation 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.

[Printed Clipping].