517 



clouds dispersed, and the weather became beautiful. All the 

 phenomena, — the direction of the gale perpendicular to that 

 in which the storm-cloud was advancing, and the sudden re- 

 versal of that direction, — seem to prove that it was a tor- 

 nado, whose centre passed directly over the place of observa- 

 tion. It is evident, on comparing the direction of the wind 

 when the whirl first reached this part of the town, with that 

 of the progressive motion of the vortex itself, that its rotatory 

 motion was retrograde, or in an opposite direction to that of 

 the hands of a watch with its face upward. It is deserving of 

 notice also, that in the northern hemisphere this is the inva- 

 riable direction of the cyclones, or great revolving storms, to 

 which the attention of meteorologists has been directed by 

 Colonel Reid and Mr. Redfield; The late storm was, how- 

 ever, different from a cyclone, both in the dimensions of the 

 vortex and in the causes from which it originated. The hori- 

 zontal section of the cyclone where it meets the earth is often 

 500 miles in diameter ; and the vortex is supposed to be the 

 effect of two crossing currents of air, which generate a move- 

 ment of rotation. In the tornado (to which species the late 

 storm belonged) the vortex is of much smaller dimensions, 

 and is produced by rapidly ascending currents of air, caused 

 by the heating of a limited portion of the earth's surface under 

 the action of the sun's rays. In the temperate zones, accord- 

 ingly, it is never produced in winter. 



" The evidence relating to the direction of the gale, and 

 its changes, as it passed over the College Park, is very com- 

 plete and satisfactory. In the park, and garden adjoining, 

 nineteen trees were rooted up and prostrated ; eleven of them 

 being trees of large size. Of these ten have fallen from the 

 south-east, or under the action of the first half of the gale, 

 and nine from the north-west. Their bearings have been ac- 

 curately taken ; and the general result is, that the mean direc- 

 tion of the south-east gale, as indicated by that of the trees, 

 is S. 56° E., and that of the north-west gale N. 53° W. 



