1854.] Report -on the Dust Whirlwinds. 375 



station, as otherwise it is difficult to imagine how the wind should 

 have continued throughout from one point." At the same time ; 

 that it was not a mere parallel current of air from the commence- 

 ment is presumed from the circumstance of the defined pillars of 

 dust being evident, and unbroken. 



By a strange omission, the direction of the wind has been neg- 

 lected to be stated, but this storm like that previously described 

 teaches that 



a. The occurrence of strati in the W. at sunset precedes the 

 occurrence of storms. 



18.— 2nd June, 1853. See chart IV. 1853. (Plate XX.) 



The early morning was very hot, with a nearly cloudless sky. At 

 9, 30 a. m. thunder was heard in W. and it was then observed that 

 a darkness prevailed there, as if rain were falling. At 10, rain began 

 to fall, with a slight breeze from W. The rain after a short time 

 fell in torrents, and the wind increased so much in violence as to 

 destroy some doors and roofs. 



In less than fifteen minutes the storm had passed over, and was 

 seen progressing N. E. as represented in the chart. 



The original notes of this storm are very meagre, but an examina- 

 tion of the chart teaches us that 



a. The circular motion of the wind was from E. to L. or con- 

 trary to the hands of a watch, and this conclusion is arrived at by 



And indeed, it may not inappropriately be presumed that many cyclones on a 

 large scale break up in this way, 



It is well known that the force of the wind on the curve corresponding with the 

 onward track is much stronger than that on the opposite, or curve of retardation, 

 and that this difference in force is occasioned by the onward progress of the 

 cyclone. When therefore we consider that between the various smaller spirals 

 that go to constitute the " storm" there is this tendency to retardation in their 

 circular motion, and that it is increased considerably by the mere friction of the 

 adjoiuing current, as well as by the circumstance that the adjoining borders of 

 different spirals are revolving in opposite directions, it seems to me that the very cir- 

 cumstance of two combined motions existing, must tend of itself to sooner or later 

 destroy the force and consequent danger arising from these phenomena, and in fact 

 that the more powerful these influences are, the more rapidly is the breaking up 

 of a storm brought about. 



3 d 2 



