1870.] Meteorology. 121 



England ; but on that evening a current of polar air began to flow 

 southwards, causing a fall of temperature of 40° within ten or twelve 

 hours at several stations (35° at Marchmont Dunse in seven hours), 

 and producing the unusual phenomenon of a smart night-frost 

 before the end of August. 



The same number of the journal contains a paper by Mr. 

 Milne Home "On Botatory Storms," which he seeks to explain 

 by the analogy of other known atmospherical disturbances. The 

 paper, which is well illustrated, consists of a series of extracts from 

 the reports of various observers of waterspouts and whirlwinds 

 which they have witnessed, and from Dr. Baddeley's work on the 

 Dust-storms of India. The reasoning on the data thus collected is 

 very brief, and not altogether satisfactory. Mr. Home assumes that 

 all our ordinary storms are simply gigantic whirlwinds, generated 

 by some unknown agency, probably the friction of interfering air- 

 currents at a high level in the atmosphere. Two such currents 

 would generate a vortex of conical shape, with great barometrical 

 rarefaction in the centre, of which the point may reach the earth, 

 and produce a reduction of pressure and a great disturbance of the 

 atmosphere. There are, however, several flaws in this chain of 

 reasoning, not the least important of which is the attempt to explain 

 the sudden fall of temperature in the rear of the storm, which 

 accompanies the north-west wind felt there, by the supposition that 

 the centrifugal force of the vortex throws out a mass of heated 

 air into the upper region of the atmosphere, and thereby dis- 

 places the colder strata at that level, forcing them down to the 

 ground. 



A more important paper on a cognate subject is Mr. Blanford's 

 investigation as to the origin of the Calcutta cyclone of Nov. 1, 

 1867, which appears in vol. xvii. of the Koyal Society's 'Pro- 

 ceedings.' Mr. Blanford is led by the data he has collected to the 

 belief that the cyclone was generated on Oct. 27 in the neigh- 

 bourhood of the Nicobar Islands. For a day or two previous there 

 had been a barometrical depression at that point, when three dis- 

 tinctly-marked wind-currents commenced flowing round it, and 

 ultimately coalesced to form the cyclone. 



If this idea be true, it would tend to show that the origin of 

 the barometrical depression, the nucleus of the storm, was to be 

 sought for in some agency independent of the mutual action of the 

 wind-currents, a result apparently at variance with the general 

 tendency of Mr. Meldrum's investigations into the analogous 

 storms of the South Indian Ocean, which appear to indicate, as 

 already remarked by us, that the barometrical depression is gene- 

 rated between pre-existing currents of air which subsequently form 

 tangents to the cyclone. 



The Beport of the Meteorological Committee for Calcutta for 



