172 ON TWO STORMS EXPERIENCED THROUGHOUT THE UNITED STATES, 
The wind had been blowing from the southward about the same time, and with the same 
force, as February 17. : 
On the morning of February 2, 1842, the temperature in Arkansas was 20° above the 
mean. ‘The winds were southerly, and had been so for the preceding day over a con- 
siderable district, in which time the wind might have travelled ten degrees of latitude. 
Temperature of Havanna, latitude 23° 10’ in winter is 72°.22, 
™ Natchez, “ 31 384 “ . 50 .32 
Effect of latitude, . ‘ j 8°: 24’ 21°.90 
Or 26°.1 for ten degrees of latitude. 
We may thus make a liberal allowance for loss of heat in travelling northward, and 
still explain the whole effect observed. February 3, 1842, in the morning, the ther- 
mometer, in the western part of Pennsylvania, stood 30° above the mean; the same in . 
the centre of New York state in the evening; and also throughout the 4th, in the vicinity 
of Philadelphia. February 3, at Pittsburgh, the wind had been blowing about thirty 
hours from the southward, in which time it might have travelled 12° of latitude, giving 
an elevation of about eighteen degrees, which, allowing for the loss of heat in travelling 
northward, is not more than half enough. Our explanation, ‘then, seems to fail. It 
should be remembered, however, that in estimating the effect of a particular storm, our 
standard should be, not the mean temperature of a long period of years, but rather of a 
few days just preceding the storm. ‘The temperature of January, was, throughout most 
of the United States, five degrees above the mean. Allowing also, five degrees, for 
radiation, we have only an effect of twenty degrees to be explained. About half of this 
effect may be ascribed to simple change of latitude; and when it is remembered that 
over a large area in the south-west, the thermometer stood 20° above the mean, and that 
this heated air was transported mostly towards the north-east, we have a cause sufficient 
to explain the whole effect in question. 
To explain the cold which succeeds the storm. After the storm of February 4, the 
thermometer no where sunk much below the mean. A north-west wind succeeded the 
storm, yet it was not of long continuance, and its cold was neutralized by the extraor- 
dinary elevation of temperature which preceded it. After the storm of February 16, the 
thermometer generally sunk 20° below the mean. This wind was very strong, and pro- 
bably travelled full ten degrees of latitude. After the storm of December 20, 1836, the 
thermometer, in the neighbourhood of the Mississippi, sunk from 30° to 40° below the 
mean. The entire month of December, 1836, was a little below the mean, but not more 
than a degree or two. It seems necessary to admit that this current travelled more than 
fifteen degrees of latitude; a supposition, I think, not inadmissible. 
II. CAUSE OF THE RAIN, 
We may be guided in our inquiry for the cause of the rain by comparing the circum- 
stances of two extreme cases, where no rain falls and where it falls most abundantly. 
Such an example we find in India, At Bombay the average fall of rain is eighty inches, 
