76 On the Whirling Action of the 



with the rotative and progressive forces, seem to combine their 

 influence in the closing rush towards the heart of the receding 

 vortex. This appears to account for the nearly opposite direc- 

 tions of prostration found on this side, and it is apparently by this 

 more violent closing action, that many trees which were first 

 overthrown in a direction nearly across the centre of the path, 

 were again moved from their position, or swept onward nearly in 

 the course of the tornado. It is proper to remark here, that an 

 attentive examination of these effects has served to convince me 

 that on the right and more central portions of the track the pros- 

 trations for the most part take place either at the outset or under 

 the middle portions of the whirlwind ; while on the left or re- 

 verse side, up to the line of the apparent axis, and even across 

 the latter, they occur chiefly under the closing action of the whirl, 

 as above described. The violent effects of this central and clos- 

 ing action are more clearly seen as we advance from the left-hand 

 margin towards the centre or apparent axis of the path. 



From the causes to which I have just alluded, the effects are 

 usually more violent on and near the hne passed over by the axis, 

 than in other portions of the track. This line of greatest vio- 

 lence is found to coincide nearly with the line which separates 

 the inwardly inclined prostrations of the two opposite sides of the 

 track.* The latter line or apparent axis of the track is some- 

 times called the line of convergence, and is indicated on the fig- 

 ure by the line and arrow c c. Along this line, from the causes 

 just mentioned, aided also by the elevating forces about the axis, 

 many of the trees are swept onward, and left with their tops in a 

 direction nearly parallel to the course of the tornado ; forming an 

 apparent, but not a just exception, to the more lateral direction 

 which pertains to most of the trees prostrated by the onset of the 

 whirlwind, near the central portions of the track. Indeed, the 

 central or closing violence of the advancing whirl is here so great, 

 that the trees are not unfrequently torn out of the ground and 

 carried onward to considerable distances. 



It is proper to state here, that in the tracks of all the tornadoes 

 which I have had opportunity to examine, and in some, at least, 



* The line of greatest violence, for the most part, is found somewhat to the right 

 of the line of convergence. 



