~ years. © The cause of this universal fog is not yet ascertained. ae 
On Storms and Meteorological Observations. 369 
through it, that when collected in the focus of a burning glass they 
would scarce kindle brown paper. Of course their summer effect 
in heating the earth was exceedingly diminished. Hence the sur- 
face waseasily frozen, and the first snows remained on it unmelted_ 
and received continual additions. Hence perhaps the wi of 
1783-4 was more severe than any that had happened for many 
“In my descent from Pittsburg to Louisville, I found the wi 
meeps about two days, constantly blowing up the river. 
north west or south west winds in fact continue almost three uart arters 
of the year. ‘The deep valley which the river has excavat 
a vortex, into which the rarefied air of the land rushes for equi bri- 
um. ‘The south west ‘wind is uniformly, at this season of the year, 
(latter part of November,) attended with a dense and bluish-atme 
phere, charged with vapors, which — like hoon etime: 
accumulate so as to obscure the lan 
“Among the more remarkable edad of the sndtearil season in 
this country, (Arkansaw,) is the aspect of the atmosphere, which in 
all directions appears so filled with smoke as often to render an object 
obscure at the distance of one hundred yards. > south west winds 
at this season are often remarkably hazy, but here the effect is great- 
ly augmented by the burning of the surrounding prairies.”> = 
on the Harmattan, in the Philosophical Tralee 
for i ve extremely dry wind in Africa, coming from the ne 
east, drying even potash. It generally brings a fog of some unknown. 
nature, ”*t Humboldt promised a discussion of the subject of dry fogs 
in the Personal Narrative, but it is to be expected of a book a quarter 
of a century in publication that some rea promised in it will be for- 
gotten and omitted. 
It is very desirable to hie the atmospheric changes on the east~ 
€rm and western sides of the Alleghanies connected and compared, by 
means of a series of good observations; but in the case of the 
the fact noticed by Mr. Nuttall must be attended to—that th 
along the beds of large streams, or in the neighborhood 
determine nothing precisely in regard. to the direction ° ot the main 
Currents of the great aerial ocean. : 
University of North Carolina, June 7, 1831. si et 
* Franklin’s Works, Vol, il, p. 288. es i 
+ Nuttall’s Travels, pages 35 and 217. 
¢ Young’s Philosophy, Vol. II, p. 458. 
“hee 
ee 
