| 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 notion that a body may be cooled almost to the freezing-point, in a hot Summer day, by the action of heat alone, is, then, erroneous. But still, the amount of heat which is used up in evaporating stagnant water from undrained land, that might otherwise go towards warming the land and the roots of crops, is a very serious loss. The difference in the temperature of a body, resulting from evaporation, may reach 25 deg. in the desert interior of the American continent; but, in the Eastern States, it is not often more than 15 deg..