276 Rotary Action of the Providence Tornado. 
taining a violent whirlwind action, must come in horizontally, 
and in the same gradually involuted courses; or, must descend 
in like manner from a higher region, in and around the outward 
parts of the whirling cone. I have long since been led to believe 
that this impulsive accession comes from both these sources, but 
chiefly from the latter ; and that this motion of accession and 
support is spirally downward in the outward portions of the 
whirl. The latter being, in its higher portions, often greatly ex- 
panded, as noticed by Mr. Allen. 
The evidence on which this opinion rests, can be but partially 
alluded to here; but I will suggest the following considerations : 
—l. The ascertained existence of a stratum of unusually cold 
air in the higher region of clouds, on some particular days re- 
markable for the occurrence of numerous thunder gusts and tor- 
nadoes:* 2. The observed descent of a portion of the clouds in 
front of the nucleus or body of a heavy;squall or tornado, which 
may sometimes be traced by the eye as low as the existing limit 
of condensation will afford opportunity for observation: 3. he 
fact noticed by Mr. Allen and others, that adjacent “to the exte- 
rior edge of the circle of the tornado” or whirlwind, the previous 
breeze often continues “to blow uninterruptedly from. the same 
quarter” as before :+ 4. The last fact, when taken also in con- 
nexion with certain peculiar and striking effects in the outward 
portions or edge of the tornado, a knowledge of which I have 
gathered from various sources: 5. The coldness of the air which 
has been noticed at the edge of a whirlwind: 6. The instant 
penetration of the lower end of the whirlwind into thick forests, 
and into hollows and ravines, which has been frequently noticed: 
7. The direct memorials of downward action in the outward por 
tions of the whirl which I have myself met with, on the tracks 
of different tornadoes. 
* This change of upper temperature I think can be clearly made out on the day 
of the New Brunswick tornado, which was but one of many tornadoes and thun a 
i peared in this part of the United States on the same day ; and 
ew Jersey, Connecticut, Massachusetts and Rhode Islan 
ist 15, 1787. I can also refer to many more recent cases of 
error of the 
air to have 
a. eee 
io here quoted is one of many which show the 
za mn which alleges a circuit or annulus of calm 
ee 
