396 Royal Irish Academy. 



jected on a sky of a paler tint, while the rugged outliers from the 

 mass, of the peculiar form (between cirrus and cumulus^ which in- 

 dicates a high degree of electrical tension, showed plainly that a 

 storm was approaching. About half-past three o'clock it burst 

 forth. The flashes of lightning (generally forked) succeeded one 

 another with rapidity, and at length the roar of the thunder seemed 

 continuous. Some persons who observed the phsenomenon from a 

 distance were able to distinguish the two strata of oppositely elec- 

 trical clouds, and to see the electrical discharges passing between 

 them. 



" Hitherto the wind was light, and there was that peculiar close- 

 ness in the air which is the result of high temperature and excessive 

 humidity. Shortly before four o'clock the rain commenced — this 

 was followed almost immediately by discharges of hail, and at four 

 P.M. the terrific tornado, which was the grand and peculiar feature 

 of this storm, reached us. 



" This gale, which appears to have been a true whirlwind, first 

 sprang up from the S.E., driving the hail before it impetuously. It 

 then suddenly, and apparently in an instant, shifted to the point of 

 the compass diametrically opposite, and blew with increased violence 

 from the N.W. The noise about this time of the shifting of the 

 wind was terrific, and arose (as is conjectured respecting similar 

 tropical phsenomena) from the confused conflict of hail in the air. 

 The size of the hailstones, as well as the vehemence of the gale, ap- 

 peared to be greater during the second phase of the storm than in 

 the first. These masses, many of which were as large as a pigeon's 

 egg, were formed of a nucleus of snow or sleet, surrounded by trans- 

 parent ice, and this again was succeeded by an opake white layer, 

 followed by a second coating of ice ; in some of them I counted five 

 alternations. 



" In less than ten minutes the tornado had passed. The wind 

 returned to a gentle breeze from the S.W., and the weather became 

 beautiful. All the phaenomena — the direction of the gale perpendi- 

 cular to that in which the storm cloud was advancing, and the sud- 

 den reversal of that direction — seem to prove that it was a true tor- 

 nado, whose centre passed directly over the place of observation. 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 mo- 

 tion of the vortex itself, that its rotatory motion was retrograde, or 

 in an opposite direction to that of the hands of a watch. It is de- 

 serving of notice also that this is the invariable direction in the north- 

 ern hemisphere 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, however, diflferent from a 

 cyclone, both in the dimensions of the vortex and in the causes from 

 which it originated. The horizontal section of the cyclone where it 

 meets the earth is often 500 miles in diameter; and the vortex is 

 supposed to be the eff"ect of two crossing currents of air, which ge- 

 nerate a movement of rotation. In the tornado, to which species 

 the late storm belonged, the vortex is of much smaller dimensions. 



