150 ON THE STORM EXPERIENCED THROUGHOUT THE UNITED STATES 



then, though the barometer may indicate every where the same pressure, the 

 wind will blow, at the surface of the earth, from the colder to the warmer sta- 

 tion; from the one where the dew point is lowest, to that where it is highest. 

 In the upper regions of the air the current will, for the same reason, be re- 

 versed. The rotation of the earth is indirectly one of the most powerful causes 

 of wind. Of itself it would produce no wind. When the earth first began to 

 revolve upon its axis, the atmosphere, it may be supposed, would be left be- 

 hind, and a wind would result, blowing with the velocity of the earth's motion. 

 By friction upon the earth's surface, the air would, however, soon acquire the 

 same motion with that part of the earth upon which it rested, and a universal 

 calm would result as truly as if the earth were at rest. If authority is needed 

 in support of this conclusion, we have that of Laplace. The earth's rotation, 

 then, is not an independent cause of wind, although some have entertained a 

 contrary opinion. But when one of the other named causes would alone pro- 

 duce a south wind in northern latitudes, the earth's rotation converts it into a 

 south-west wind; and in like manner a north wind is converted into one from 

 the north-east. Several other causes of wind might be enumerated, but it is 

 believed that their action is comparatively feeble and unimportant. 



Bearing in mind these preliminary principles, let us proceed to analyze the 

 observations of the wind on pages 137 — 139. To do this the more conveni- 

 ently, I furnish myself with a large number of small bits of paper, each having 

 the figure of an arrow, and spreading out before me a map of the United States, 

 I place at each station an arrow, representing the wind's direction for the pe- 

 riod under comparison. I thus have a graphic representation of all the obser- 

 vations. Beginning, then, with the observations of the morning of December 

 ISth, we find the barometer at an unusual height along the line of the Missis- 

 sippi river, while, in the eastern states, it was quite low, but rapidly rising. 

 The wind, at places east of Detroit, we find very uniformly blowing from the 

 west. Where there is a deviation from this rule, it is usually to the north- 

 west; and in one case only, Alleghany Arsenal, was the wind from the north. 

 Near the southern border of the United States the wind was from some north- 

 ern quarter, except at Natches, where it was east. The rise of the barometer 

 which was experienced in the United States was nearly insensible south of the 

 parallel of 28°, and hence a tendency of air in that direction. Along the valley 

 of the Mississippi the barometer was at its maximum ; the winds consequently 



