170 ON TWO STORMS EXPERIENCED THROUGHOUT THE UNITED STATES, 
I. OSCILLATION OF THE THERMOMETER. 
Both of these storms, as well as that of December 20, 1836, were accompanied by a 
considerable elevation of the thermometer. Under this last storm, the thermometer rose 
20° above its mean height; February 17, 1842, it rose the same; and February 4, 1842, 
it rose 30° above the mean. What is the cause of this extraordinary temperature? 'The 
three following causes may be supposed to contribute to the effect. 
1. Diminished radiation, in consequence of the sky being covered with clouds. 
2. The heat evolved in the condensation of vapour. 
3. The transfer of air from a more southern latitude. 
The first of these causes can have but a limited influence. We may estimate the 
amount by comparing the means of observations made in clear and cloudy weather. 
The observations on the accompanying charts correspond about to the hours of sunrise 
and sunset. 'The following results I have deduced from observations made by Mr. Bond, 
at Cambridge. Column first shows the mean temperature, at sunrise, when the cloudi- 
ness was less than five tenths; column second, the temperature of the rest of the month, 
CLEAR. | CLOUDY. DIFF. 
December, 1841,) 21°.4 30°.1 S79 
January, 1842,| 16 .6 30 .8 14 .2 
February, 1842,| 20 .4 31 .2 10 .8 
Mean, ’ ; : ; . 11 .8 
According to these observations, in the winter, at Cambridge, the thermometer for 
clear mornings, stands 5°.9 below the mean, and on cloudy mornings the same above. 
We may estimate the effect of radiation then, at 5°. We have still to be accounted for, 
an elevation of 15° in two storms, and of 25° in the other. Can this be ascribed to 
the heat evolved in the condensation of vapour? ‘The heat evolved in the precipitation 
of one inch of water, is sufficient to raise the temperature of the surrounding atmosphere 
about ten degrees. ‘The fall of water, in these storms, was very great. Does not this 
explain the whole rise of the thermometer? I infer not, for the following reasons: 
1. The rise of the thermometer was not proportioned to the amount of rain. Thus in 
the storm of February 4, the rain averaged three inches for a large area in the south- 
west; in Ohio, about two inches; in New England, one inch. The greatest rise of the 
thermometer in the south-west, was 20°, and in New England, 30°. 
2. In tropical countries, where the range of the thermometer is least, the fall of rain is 
the greatest. Thus at Singapore, latitude 1° 20’ north, according to a register published 
in Silliman’s Journal, Volume xliv., page 151, the entire range of the thermometer for 
sixteen months was 21°.3, while the fall of rain for one year was ninety-three inches. 
At Bombay, the average fall of rain for June is twenty-four inches, and the same for 
July. More than twice this quantity has repeatedly fallen in one month. June 23, 1817, 
9.03 inches of water fell, and on the next day, in a period of nine hours, 7.23 inches fell, 
yet the entire range of the thermometer, for the month, was only 12°, and the thermome- 
