of the Providence Tornado. 47 
other objects 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 re- 
lates to the earth’s surface. Thus the squares of these effect- 
ive velocities will give a power relatively equal to 100 at the 
former point and only 36 at the latter; both being equally di- 
stant 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 respect- 
ive 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 mo- 
tion of the tornado, receive a direction more onward than is 
represented by the arrows or lines in the figure, which can re- 
present only a stationary rotation. 
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 quadrant. 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 further advance of the tornado, unless very 
near to its axis. Moreover, if one tree should fall when under 
the more advanced portion 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 pass- 
ing into the second quadrant, on the left side of the track, is 
sweeping 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 effect- 
ive power is here greatly reduced, and gives fewer prostrations 
than under either the first or third quadrants. The minimum 
of effect occurs on the arrival of the line e /, at the rear of the 
second quadrant. 
