re” > i eee ec oe 
Rotary Action of the Providence Tornado. 273 
jects encountered by it, is as the square of the wind’s velocity at 
the point of impingement, the relative effects on the two sides of 
the line of the axis, which before were equal, will now be greatly 
altered. 
For, if at a given distance on the right of the advancing axis, 
the former velocity was 80, it will now, as relates to the earth’s 
surface, have become 100; and at the same distance on the left 
side the velocity of the wind will be reduced to 60,; as relates to 
the earth’s surface. Thus the squares of these effective veloci- 
ties will give a power relatively equal to 100 at the former point 
and only 36 at the latter; both being equally distant from the 
axis. Hence, although the rotative velocity of the whirl decreases 
rapidly as we recede from its axis, yet its prostrating power will, 
by its progressive motion, become greatly extended on the right 
side of the advancing axis, and proportionally contracted on the 
left side. 'Thus the respective boundaries of the prostrating power 
on the two sides of the tornado, when thus in motion, may be 
those indicated on the figure; which nearly correspond to the 
effects which have been observed in several cases. 
It may be seen further, that nearly all the prostrations near the 
line of the axis and elsewhere, must, by the advancing motion 
of the tornado, receive a direction more onward than is represent- 
ed by the arrows or lines in the figure, which can represent only 
& stationary rotation. ee yi itiois ere rss) 
In further considering these effects, in different portions of the 
Whirl, as it encounters objects in its advance, we shall find the 
maximum effects to be mainly on the line a, 7, 0, at the rear of 
the first quae Hence, if a tree on this side the axis should 
fail to be prostrated till after the first quadrant had passed over, 
it would not be likely to fall in the fourth quadrant, on the fur- 
ther advance of the tornado, unless very near to its axis. More- 
over, if one tree should fall when under the more advanced por- 
tion of the first quadrant, another if prostrated later in the same 
quadrant, must necessarily fall in a more onward direction than 
the first, and if sufficiently near will lie across the latter. 
It may likewise be seen, that the wind of the whirl in passing 
into the second quadrant, on the left side of the track, is sweep- 
ing backward, and with its effective power thus greatly reduced, 
as regards fixed objects on the earth’s surface. Thus the limits 
of prostration are not only narrowed, but the effective power is 
Vol. xt, No. 2.—July-Sept. 1942. 35 
