1852.] Notes on Dust Whirlwinds and Cyclones. 335 



17. — Once, when observing the peculiar motions of a well defined 

 slender dust pillar, rotating briskly, but at the same time remaining 

 almost stationary on the one spot, and while looking upwards at the 

 body of the column, with the view of understanding the particular 

 course the dust was taking in its ascent, the pillar was suddenly with- 

 drawn, or lifted upwards, and carried out of sight — and this occurred 

 so suddenly as to give the impression of its having been divided 

 asunder ; particularly as the outer stratum of dust remained for a 

 few moments suspended in the air — but, on again directing the eye to 

 the earth, the absence of the rotatory motion and of the cone of dust, 

 at once explained the real state of the case. 



18. — In March last, during unsettled stormy weather, my attention 

 was directed to a large mass of dust whirlwinds to the Northward, 

 moving from West to Eastward — all at once, their course was entirely 

 changed — and they were seen coming back from N. E. to S. W. 



This strange and sudden shift, may perhaps be explained, by sup- 

 posing that the mass of spirals moving in a cycloidal course, recurved 

 at that particular time. 



19. — I once followed, for more than a mile, a dust whirlwind of 

 about four or five feet in diameter, travelling at the rate of seven or 

 eight miles an hour, and rotating from right to left Q), After a time, 

 its progress was retarded, so as to enable me to penetrate to the cen- 

 tre, and to walk slowly with it for a short distance. The centre was 

 perfectly calm, while, round about, the wind was blowing in every 

 direction. Though surrounded by dust, I was enabled, by keeping my 

 eye fixed upon the whirling line of dust at my feet, as it continually 

 swept past me on the right, (the side of progression,) to preserve my 

 position in the central calm space, for some little time, without being 

 inconvenienced by the dust. On the left hand side of the whirl, the 

 dust was not so well defined, but cloudy and confused. 



There was in this case, as in all others of a similar kind, a trail of 

 dust closely following, occasioned by the action of the whirlwind upon 

 the air. 



20. — Westerly winds, or rather West South West winds, seem almost 

 invariably to prevail at Lahore at the height of three or four miles 

 above the Earth's surface — in the region of Cirro Stratus and Cirrus. 



When clouds prevail, with fine weather, they usually clear off about 



