334

CLIMATE OF NORTH AMERICA.

The prevalence of a current from the south-west in theseStates on the morning of 10th November, is remarkable. Thevariations in the directions of the winds at the earth’s surfacemay be referred to irregularities of the country, and to theinfluence of local rains, which draw the winds towards them.There is much less irregularity in the cold westerly windsthan in the southerly, as they do not precipitate much mois-ture unless over the country where they raise the southerlywinds into the upper current.

Had we only traced the changes of winds and temperatureson the 10th and 11th November, from St. Louis, in Missouri,to Ann Arbour, in Michigan, that is, from south-west to north-east, there might have been some grounds for believing thatthese changes were propagated from south-west to north-east.But more extended observations show that they were nearlyfrom west to east. The south-westerly winds that prevailedalong the greater portion of the Atlantic coast, on the morn-ing of the 13th, were cut off on the Atlantic coast of Floridaby the north-west winds * in precisely the same manner asthe southerly winds of Michigan were by the north-westerlywinds of Missouri, on the morning of the 10th November.Franklin, it has been seen, confined his observations to theAtlantic coast which runs from south-west to north-east;hence his error of supposing that the American storms fol-lowed the line of the coast. Franklin’s observation, asalready stated, is quite reconcilable with that of Espy, -whichhas been corroborated by Loomis, that winter storms travelfrom west to east.

We find changes of temperature brought about in theStates of Alabama, Georgia, and Florida, on the 12th Novem-ber, in a manner similar to that which took place in Indianaand Wisconsin on the 10th (Plate 7). The north-westwind, in approaching the Atlantic coast, flows underneath thewarm southerly current from the Gulf of Mexico, and raisesit into the upper current, which is constantly from the west.Thus, the north-west wind had reached Tuscalooza, Alabama,and Warrington navy-yard, West Florida, on the morning ofthe 12th; but the country to the eastward was everywhere* See Plate 3.