332

CLIMATE OF NORTH AMERICA.

action in the country over which they yet prevail towardsthe north-east. They blow on as if no change had occurred inthe south-west. The same process is going on all to thesouthward; for, as is Been by the large chart of the weatherof 10th November, northerly winds are prevailing at FortSmith in Arkansas, and the temperature is 12° lower than atOttowa in Illinois, where the temperature is still one degreehigher than at New Weid in Texas, which is below the 30thparallel of latitude.

The southerly wind that appeared as an unbroken cur-rent in the morning of the 9th from Fort Brown to Fort Snel-ling, was in course of being displaced by the cold west wind,and a rapid reduction of temperature ensued. The displace-ment was going on nearly on the same meridian for 1200 milesat least. From the sudden fall of temperature that ensued asthe wind at any station changes from the south-west to the westor north-west, as well as from the fact of this taking place ina long line on the same meridian, it is evident that this was nota veering or curving of the south-west wind. The directionsof the winds on the charts are completely opposed to thisview. Various hypotheses have been proposed to explainthe changes that take place in the directions of the windsduring the American storms, which I believe are all similarin their action to that which occurred from the 9th to 14thNovember 1854. If the small chart (Plate 7) is againexamined, we see that the winds at Milwaukee and FortSnelling were blowing right toicards each other ; the one having atemperature of 52°, the other of 22°. But by 2 p. M. the south-east wind disappeared at Milwaukee, and the north-westhad taken its place, and lowered the thermometer to 38°.According to Professor Loomis, the south-east wind ascendsin consequence of the north-west flowing under it, and a partof it is carried to the south-east and a part to the north-west.I agree with Loomis that the north-west flows under the south-east wind, but it is very evident that the whole of the south-east flows towards the east as it is raised into the uppercurrent that prevails so constantly from the west or north-west.This readily explains the change of wind which so often takesplace from south-east to north-west, and also the great reduc-