THUNDER-STORMS.

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naturalist at Washington, informed me that this phenomenonis so constant, and the course of the thunder-clouds is sonearly from west to east, that in going out there to walk, henever thought of taking an umbrella, if the thunder-cloudswere a little to the south or to the north of due west; but ifthe clouds were due west, he was sure to have rain. Onthe other hand, in the New England States and Canada, thethunder-clouds usually drift from a point or two north of westto a point or two south of east, at the same moment thatthe southerly wind blows at the earth’s surface. *

In the first thunder-storm that I encountered in theUnited States, I was rather struck with the phenomenon ofthe clouds drifting in the upper current from the west, whilethe wind blew from the south. It occurred at Saratoga onthe 6th September 1854. At sunrise the temperature was70° with a dew point of 69°; the thermometer at 2 p.m.reached 96°. Notwithstanding the great heat, the wind blewstrongly from south by west, but thunder-clouds floated in theupper current from the north of west. Thunder with muchrain occurred at night, and next day the wind changed to thenorth of west, and the sky became beautifully transparent,with the thermometer at 82° at 2 p.m.

The cause of this peculiar action of the thunder-cloudsfloating at. a higher elevation, at right angles to the warmsoutherly wind, is easily explained. So long as the wind iswest or north-west in summer, the sky retains its transpa-rency ; but when it changes to a southerly quarter, it doesnot blow more than a day or two before clouds begin toform. The clouds do not often float in the south wind, butalmost always in that upper current which prevails so con-stantly from the west. This clearly shows that the uppercurrent rubs off a portion of the moist and hot wind fromthe Gulf of Mexico, and forms clouds, for they only appearafter the southerly wind blows for some time, and these cloudsreveal the existence of the upper current. This action ofthe upper current robbing the lower is constantly taking place,both in summer and in winter, when clouds form and driftin the upper current.

As the heat and moisture increase in the south winds2 A