below.

QUANTITY OF WATER EVAPORATED, IN INCHES, VERTICAL DEPTH.

| Whitehaven, | |
| England, | Ogdensburg, | Syracuse,
| mean of | N. Y., | N. Y.,
| 6 years | 1 yr. | 1 year
--------+-------------+-------------+------------
_Jan._ | 0.88 | 1.65 | 0.67
_Feb._ | 1.04 | 0.82 | 1.48
_Mar._ | 1.77 | 2.07 | 2.24
_Apr._ | 2.54 | 1.63 | 3.42
_May._ | 4.15 | 7.10 | 7.31
_June._ | 4.54 | 6.74 | 7.60
_July._ | 4.20 | 7.79 | 9.08
_Aug._ | 3.40 | 5.41 | 6.85
_Sept._ | 3.12 | 7.40 | 5.33
_Oct._ | 1.93 | 3.95 | 3.02
_Nov._ | 1.32 | 3.66 | 1.33
_Dec._ | 1.09 | 1.15 | 1.86
--------+-------------+-------------+------------
_Year._ | 30.03 | 49.37 | 50.20

The quantity for Whitehaven, England, is reported by J. F. Miller. It
was very carefully observed, from 1843 to 1848--the evaporation being
from a copper vessel, protected from rain. The district is one of the
wettest of England--the mean quantity of rain, for the same time, having
been 45.25 inches.

This shows a great difference in the capacity of the air to absorb
moisture in England and the United States; and as evaporation is a
cooling process, there is greater necessity for under-draining in this
country than in England, supposing circumstances in other respects to be
similar.

Evaporation takes place at any point of temperature from 32 deg., or lower,
to 212 deg.--at which water boils. It is increased by heat, but is not
caused solely by it--for a north-west wind in New-England evaporates
water, and dries the earth more rapidly than the heat alone of a
Summer's day; and when, under ordinary circumstances, evaporation from a
water-surface is slow, it becomes quite active when brought in close
proximity to sulphuric acid, or other vapor-absorbing bodies.

The cold which follows evaporation is caused by a loss of the heat which
is required for evaporation, and which passes off with the vapor, as a
solution, in the atmosphere; and as heat leaves the body to aid
evaporation, it is evident that that body cannot be cooled by the
process, below the dew-point at which evaporation ceases. The popular
no