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 eaiLh'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 

 a stationary rotation. 



In further considering these effects, in different portions of the 

 whirl, as it encounters objects in its advance, v/e shall find the 

 maximum effects to be mainly on the line «, «, o, at the rear of 

 the ^rs^ 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 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 raore 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. xLiii, No. 2.— July-Sept. 1842. 35 



