- 
186 Whirlwinds produced by the burning of a Cane-Brake. 7 
5. As the fire spread rapidly from different points, it was at 
length circular in outline, or approached this form. It was not — 
until the heated air was rising from this circle that the whirlwinds 
became frequent-in number or of great size. 'The same phenom- 
ena are shown on a small scale in the common process of putting 
tire on wheels, where the whole body of air and smoke above the 
fire appears full of eddies and whirls. If these fires are made ina 
_ yard surrounded by high buildings, the effect is greatly increased. 
In some situations of this kind, whirlwinds of quite regular forms 
and fifteen or twenty feet high, are sometimes seen. But owing — 
to the dry wood of which these fires are usually formed, and the — 
very small amount of light colored smoke which is produced by — 
this wood, it is generally difficult to determine the exact forms 
which the whirls assume ; yet at different times all the kinds 
described in this article have been observed. 
hese facts have a bearing upon the method which has been 
proposed of producing rain by circular fires. It has been maib- 
tained that if a circular fire were created the air would be made 
to ascend in a single column, a cloud would be formed in the up- 
per part of this column or at the top, and this cloud being thus 
formed, would subsequently produce rain. The whole theory, 
therefore, depends upon the first supposition that the air would 
ascend ina single column ; but from the phenomena which at- 
tended the burning of the cane-brake, I have been led to the con- 
clusion, that, unless the mass of combustibles were very great, and 
the fire very intense, no single column of rarefied air, in the ma- 
jority of cases, would be formed, and, consequently, the phenom- 
ena dependent (as it is maintained) upon this supposition would 
not take place. The great heat produced by the burning of the 
canes appears, from the fact that we were obliged to move from @ 
station within two hundred yards of the fire to one distant about 
three hundred yards, and even at this distance the heat of the fire 
was so strong that most of the company present were at a distance 
still greater. In all the cases mentioned in the Journal of Science, 
the mass of combustible matter was very great, and, in one case 
at least, was piled up towards the center. 
e location of the cane-brake was very favorable to the 
formation of whirlwinds, being a river bank, to a great extent 
surrounded by woods and higher land. It corresponded in some 
egree to the fires for putting tire on wheels when these are kindled 
in an inclosure partly surrounded by buildings. I have been 
informed that the whole air of a large space thus inclosed 1s 
sometimes affected by these fires and put in motion ina direction — 
Opposite to the beneral course of the wind. A rotary motion 
‘sometimes pervades the air of these places. - 
a3. In the midst of the fire the foliage of the trees (No. 6,) be- 
came gradually dried and parched, and finally caught on fire, 
g almost with a flash like powder, and adding greatly to U 
