190 Pccllcr and Cronible — On the Tornado ivJuch [No. 2, 



In reference to the connection which Mr. Finley appears to find 

 between the passage of barometric minima and the possibility of forma- 

 tion of tornadoes, it will be remarked tliat Mr. Willson apparently traced 

 a connection between the two same facts in the case of the Satkhira 

 tornado of L872. 



According to the meteorological charts wliich. accompany Mr. Finley's 

 Memoirs, it would appear that the position of the formation of tornadoes 

 is to the south and east of the line taken during the advance of the 

 barometric minimum, and that it occupies the same relative position to 

 the high contrasts of temperature and humidity. Further, it is probable 

 that the track of the tornado bears a definite relation to the position of 

 these same violent contrasts. In all these cases, however, it is not to 

 be assumed that the tornado will be formed in close proximity to baro- 

 metric minima or to contrasts of temperature and humidity, for the 

 researches in America show that these actions may only exist long dis- 

 tances, perhaps 200 or 800 miles, away. Beyond these rather vague state- 

 ments, it does not appear safe to go, but it is clear there must be some 

 further cause or causes at work which determine the actual formation 

 of the storm, but of which at the present time we have no knowledge. 



Similar actions or contrasts of temperature and humidity brought 

 about by more or less opposing wind systems blowing in neighbouring 

 districts are common in Bengal during the hot weather season. It fre- 

 quently happens that hot, dry, north-westerly winds may be blowing a 

 short distance inland, while moist, comparatively cool, southerly or south- 

 easterly winds are blowing to the south of them, or along the coast and 

 in the neighbouring districts. Such actions usually, it is believed, pro- 

 duce the nor'westers with which all are familiar, and which are of very 

 frequent occurrence in Bengal from about February to June. The history 

 of some of these storms has been worked out by Mr. Eliot.* Experience 

 has shown that nor'-westers do not occur either w^hen a steady, hot, 

 and dry westerly or north-westerly current is blowing over Bengal, or 

 even when a steady easterly or south-easterly current heavily laden with 

 moisture is blowing over the Province, as is the case during the rainy sea- 

 son but it is required that both currents be present in different districts. 

 To state the case roughly and very briefly, it is believed that the actual 

 storm may be formed at the area of interaction by one of two causes. 

 Either the moist wind may be forced upwards above the hot, dry current, 

 when according to well known laws the mass of gas would expand and 

 cool and at once deposit a part of its moisture in the form of rain. 

 This formation of liquid water from aqueous vapour will immediately 

 set free a large amount of energy, which, perhaps, increases the ascen- 



* Indian Meteorological Memoirs, Vol. I, p. 119. 



