tion 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..

The temperature of evaporation is the reading of a wet-bulb-thermometer
(the bulb being covered with moistened gauze) exposed to the natural
evaporation; and the difference between that reading and the reading of
a dry-thermometer, is the expression of the cold resulting from
evaporation.

When the air is nearly saturated, the temperature of the air rarely goes
above 74 deg.; but, if so, the moisture in the air prevents the passing away
of insensible perspiration, and the joint action of heat and humidity
exhausts the vital powers, causing sun-stroke, as it is called. At New
York city, August 12th to 14th, 1853, the wet-thermometer stood at 80 deg.
to 84 deg.; the air, at 90 deg. to 94 deg.. The mortality, from this joint effect,
was very great--over two hundred persons losing their lives in the two
days, in that city.

From very careful observations, made by Lorin Blodget, in 1853, at
Washington, it was found that the difference between the wet and dry
thermometer was 18-1/2 deg. at 4 P. M., June 30th, and 16 deg. at 2 P. M. on
July 1st--the temperature of the air being 98 deg. on the first day, and 95 deg.
on the second; but such excesses are unusual.

The following table has been compiled from Mr. Blodget's notice of the
peculiarities of the Summer of 1853:

The dates are such as were selected to illustrate the extreme
temperatures of the month, and the degrees represent the differences
between the wet and dry thermometer. The observations were made at 3 P. M.:

_Locality._ _Dates._ _Differences._

JUNE, 1853.

Burlington, Vt. 14th to 30th ranged from 8 deg. to 17 deg.
Montreal 14th to 30th " 6 to 17
Poultney, Iowa 10th to 30th " 9 to 16
Washington 20th to 30th " 8.5 to 16
Baltimore 13th to 30th