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Published online by Cambridge University Press: 14 September 2016
A short summary of our knowledge of this subject may be of interest to readers of the Aeronautical Journal.
Dust devils, that is to say, columns of dust in rapid rotation, are occasionally seen in Agra. They only occur in hot, dry weather. Those of the largest size, having a diameter of two or three metres and a height of several hundred metres, only occur when the air is nearly calm. They travel to leeward at a speed of about four to six miles per hour. The dust, having reached the upper end of the column, spreads out into a diffuse, irregular mass, which may persist for some time after the dust devil that produced it has vanished.
Fig. i is copied from a book treating of dust devils and dust storms observed at and near Lahore (India) by P. F. H. Baddeley.
He states that they are never shaped like an inverted funnel, as is the case with whirlwinds in America, as described by Redfield.
1 P. F. H. Baddeley, “Whirlwinds and Dust Storms of India.” (London: Bell & Daldy, 1860.) (British Museum Library, No. 14000.7.12 and 8756.d.I.)
2 W. C. Redfield, “On the Spirality of Motion in Whirlwinds and Tornadoes.” London and Edinburgh Philosophical Magazine and Journal of Science, Vol. XIII. (Fourth Series), January- June, 1857, p. 223. (British Museum Library, No. RPP.61.1433.)
* In the rooms of the Royal Meteorological Society, London, is an old print showing a group of waterspouts. One waterspout is shown twisted into a loop similar to that of the looped dust devil mentioned and figured by Baddelev.
3 They are far less common in Agra than they are in the Punjaub and Rajputana. In the damp climate of Calcutta they are small, transitory, and infrequent.
4 Unfortunately, Baddeley's account is coloured by a theory that dust devils were due to “spiral threads of electro–magnetic fluid,” and that they were of the same nature as dust storms. Dust storms occasionally occur after sunset. It is extremely unlikely that real dust devils have ever been observed at this time.
5 Alfred Wegener, “Staubwirbel auf Island,” Meleorologische Zeitschrift, April, 1914, Pt. 4, Vol. XXXI., p. 199.
6 W.’ Ferrel, “A Popular Treatise on the Winds” (John Wiley & Sons, New York, 18S9.)
7 A. C. Arend, “The Effect of the Omaha Tornado on Structures,” Engineering News (New York), 1st May, 1913, Vol. LXIX., No. 18, p. 898.
8 Ferrel, loc. cit.
9 W. M. Davis, “Whirlwinds, Cyclones, and Tornadoes.” (Boston: Lee & Shepard, 1884.)
10 “Benjamin Franklin, Works of,” edited by Bigelow, Vol. II. (Putnam & Sons, NewYork and London, 1887, p. 267, Letter XCV. to John Perkins, read at Royal Society of London, 24th June, 1756.)
11 “Animal Flight,” p. 277.
12 W. C. Redfield, “Some Account of Violent Columnar Whirlwinds which appear to have resulted from the action of Large Circular Fires.” American Journal of Science and Arts (Silliman), Vol. XXXVI., July, 1839, p. 50. New Haven. (British Museum Library, No. RPP. 1435.)
13 A. F. Olmsted, “Whirlwinds Produced by Burning of a Cane Brake.” American Journal of Science and Arts, Vol XL, 1851, p. 181. (British Museum Library, No. RPP. 1435.)
14 Loc. cit., p. 10.
15 15 W. A. Douglas Rudge, “On the Daily Range of the Atmospheric Potential Gradient at Bloemfontein, and the Influence of Dust Storms.” Transactions of the Royal Society of South Africa, Vol. IV., Part I., 1914, p. 75 ; and “On the Electrification Produced during the Raising of a Cloud of Dust.” Proceedings of the Royal Society of London, A, Vol. XC, 1914, p. 256.
16 A. Wegener, “Ueber den Ursprung der Tromben.” Meteorologische Zeitschrift, May, 1911, Vol. XXVIII., p. 207. An account of Wegener's theory is given in the Scientific American of the 7th March, 1914, Vol. CX., No. 10, p. 193.
17 W. M. Davis, “Elementary Meteorology,” p. 263. (Boston : Ginn & Co., 1894.)
18 S. A. Arrhenius, “Lehrbuch der kosmischen Physik,” p. 797. (Leipsig : S. Hirzel, 1903.