272 —- Rotary Action of the Providence Tornado. 
be considered as whirling in the manner here represented, but 
without any change of location, its action may be supposed as 
concentrically equal on all sides; the motion, however, becoming 
qnickened towards the center in the inverse ratio of the succes- 
sive concentric areas: that is, each particle of air as it revolves 
about the axis, continuing to describe nearly equal areas in equal 
times, in its progress towards the center, where it rises spirally in 
the direction of discharge ; this direction being vertically at the 
center, the point or area of least atmospheric resistance or pres- 
sure. Thus, the course of a single particle, horizontally, may 
beabcdefghik;—and so on or between each of the four 
involuted lines which constitute the figure. 
wage rv: 
Lesh ae n ae of LT ost aN ogi 
UE 
ota Sa ; boundary of rhs 
For further reference, we may divide this figure by the cross 
Tines of arrow heads, into the four quadrants 1, 2, 3, 4. 
We will now consider this whirl as having a constant progres 
emo on on the line of the long arrow cc, at arate equal t 
ur th of its average rotative velocity. It will then 
‘lor hata the soe whi on era omni 
