te 
iy 
274 Rotary Action of the Providence Tornado. 
here greatly reduced, and gives fewer prostrations than under 
either the first or third quadrants. The minimum of effect oc- 
curs on the arrival of the line e k, at the rear of the second quad- 
rant. 
But on the arrival of the third quadrant, the prostrating power 
on the left side becomes more and more efficient by the ceasing 
of the backward and the accession of the progressive movement ; 
and at or near the line of fm, it again takes effect, with rapid 
increase. The destructive force is also much augmented here 
by the greater velocity of the heart of the whirl, near its axis, 
and the impetus must rapidly increase in energy to its maximum 
effect, as at mn o, taking off any tree which may here remain, 
and carrying aloft, or sweeping onward, the objects previously 
prostrated on the line ¢ zk. 
If a tree on the deft side of the track falls on one previously 
thrown down by the tornado, the last fallen will also have the 
more onward direction, as on the other side: unless both have 
fallen in the second quadrant, where few prostrations occur. —The 
_ fourth quadrant, for causes noticed in considering the first, an 
have little prostrating effect, except perhaps on the small area 
near its axis. 
If we now conceive of our figure as applied only to the limits 
of prostration or destruction which constitute the visible path 
the tornado, it becomes apparently and relatively unequal, in its 
right and left hand quadrants, the axis appearing greatly eccel- 
tric, and in the same degree, at least, as the Jeft band or belt of 
prostrations is found narrower than that on the right of the axis 
This apparent, but illusive form of the whirl, may be illustrated 
by fig. V; which is drawn on the same lines with the preceding 
figure. 
It will readily be seen that this eccentricity of the axis, 00 the 
visible track, will be in proportion to the progressive velocity 
the tornado ; other things being equal. ‘Thus, if Mr. Allen be 
nearly right in his estimate of the rate of progress in the Provi- 
dence tornado, the eccentricity shown in its path would be ge” 
erally less than is shown in figures IV and V. On the other 
and, if the progressive velocity should be as great as Professo! 
coms | me he ascribes to the tornado of February last, it 
Ohio, viz. about —: miles an. hau, the eccentricity would in 
: a case increas ws the axis as far out 
