164 ON TWO STORMS EXPERIENCED THROUGHOUT THE UNITED STATES, 
Storm of February 16, 1842. 
I have represented the principal phenomena of this storm on the accompanying charts, 
one to five. Those regions, where the sky was unclouded, or where the cloudiness was 
less than one half, are coloured blue; those where the sky was entirely overcast, or the 
cloudiness exceeded one half, but without rain or snow, are coloured brown; the fall of 
snow is indicated by the green colour, and rain by the yellow. ‘The direction of the 
wind is represented by the arrows, and its force is, to a certain extent, indicated by their 
length. When, however, the winds were faint, the arrows, if drawn of a strictly propor- 
tionate length, would have been too short to attract notice, and are therefore somewhat 
magnified. A calm is represented by a cipher, (0). I have also represented the baro- 
metric, and thermometric observations in the following manner: Having determined, as 
well as I was able, the mean height of the barometer at each station, I compared each 
observation with the mean. I then drew a line passing through all the places, where 
the barometer stands at its mean height. This line is marked — — 0, and may be called 
the line of mean pressure. I then drew a line through all the places where the barome- 
ter stands two inches above the mean. ‘This line is marked — — — +.2, and so of the 
others. In like manner, a line joining all those places where the thermometer stands at 
its mean height for that hour and month, is marked .... . 0°, and may be called the 
line of mean temperature. Another line joins all those places where the thermometer is 
10° above the mean, and is marked...... 10°, and so of the others. Nearly every 
circumstance essential to a correct understanding of the phenomena of the storm is thus 
presented to the eye at a single glance. 
Chart 1. for the morning of February 15, represents the storm near its commence- 
ment, and before it had acquired much violence, or its features had become very 
distinctly marked. In the extreme north-eastern part of the United Statés, is seen a 
corner of a storm rapidly passing off. In the vicinity of Buffalo, a few particles of 
snow are falling, and the sky in its vicinity is overcast. Perhaps this may be ascribed 
to the vapour arising from the lakes, aided by the rise of ground as the current travels 
eastward, by which means the moist air at the surface is forced up to a region of greater 
elevation and cold, and its vapour condensed. With these exceptions, nearly the 
whole eastern and central portions of the United States are unclouded. But through- 
out the valley of the Mississippi, the heavens are obscured, and in the northern part some 
snow is falling. This is the commencement of the storm which I propose particularly 
to consider. Throughout the entire United States the barometer stands a little above the 
mean. The line of ——— 4.2, is marked upon the chart. The thermometer no 
where stands much above its average for February. The line of mean temperature 
passes nearly through the middle of the United States; and that of 10° below the mean, 
is an undulating line in the eastern part of the United States. The direction of the 
winds is exceedingly various. In the eastern part of the United States, the winds are 
generally north-west, the result of the preceding storm. The weight and density of the 
atmosphere were here both greater than farther west. As you proceed westward, the 
wind moderates, becomes calm at many places, and in the central parts of the United 
States begins to set towards the west. ‘Throughout the Mississippi valley the winds are 
neither very strong nor uniform in their directions;—a result to be expected, as there 
was no where any very considerable disturbance of mean temperature or pressure. 
