prevalent Disorders, $c, with Volcanic Emanations. 19 



alter the case, whatever be the cause of the rarefaction. In 

 countries lying near the sun, it is doubtless true that the 

 heat of that luminary is the chief cause of the set of the wind ; 

 yet it sometimes occurs that, even there, a hurricane travels 

 against the course of the regular storm winds. And thus the 

 hurricane at Calcutta, lat. 22° 30' n., on May 21. 1833, blew 

 almost uninterruptedly from the n.e., which is the point op- 

 posite to that of the monsoon then blowing, though it after- 

 wards came all round the compass. This leads me to be- 

 lieve that the cause of that hurricane was a disengagement of 

 heat in the eastern volcanic band of the Moluccas; which 

 I consider somewhat established by the contemporaneous- 

 ness of the hurricane at New Orleans, from n.w., within 

 a few miles of the same distance from the volcanic band 

 of the West Indies, that Calcutta is from the Moluccas. 

 There are, however, volcanic foci nearer. The valley of the 

 Mississippi is subject to frequent earthquakes. The circular 

 course of the hurricanes in the West Indies has been ob- 

 served elsewhere. Mr. Orme {History of Hindostan) relat- 

 ing the effects of the hurricanes off the Indian coast, on 

 October 2. 1746; October 31. 1753; December 30. 1760; 

 October 20. 1763; mentions that the storms blew from all 

 points, ranging round the compass ; and that the effects were 

 not felt a few miles either way from the locality of the prin- 

 cipal mischief. Mr. Capper [On Winds and Monsoons), there- 

 fore, considers these hurricanes as whirlwinds whose diameter 

 cannot be more than 120 miles. The hurricane of March 10. 

 1770 illustrates this most admirably. The Britannia India- 

 man was taken by it from the n.e., and much injured. The 



meriting on this (Astronomy, p. 132.), says, " a rapid transfer, either way, in 

 latitude, of any mass of air," carried any how " above the reach of the friction 

 of the earth," would be " sufficient for a hurricane ; and two, for a 

 tornado." 



This heat (of the sun) is communicated to the " air near the surface 

 of the torrid zone, which being thereby. rarefied ascends ; and its place is 

 supplied by colder air, which rushes in from the north and south." {Thom- 

 son.) It is obvious how the powerful ascending draught of air which con- 

 stitutes a hurricane, and which acts so strongly in depressing the barometer, 

 will have an equal effect in setting loose the imprisoned winds of the 

 earth. (Poidett Scrope, On Volcanoes, p. 60.) 



To show the effect of aerial convulsion, however produced, the follow- 

 ing fact is advanced: — The roof of a quarry, at Parnay, near Saumer, in 

 France, fell in, in the last week of December, 1833, at two o'clock, a.m. 

 The depth of the displaced materials was twenty yards, and the width 

 about 400 yards. Now, the concussion of the air thus produced drove a 

 heavy waggon and a barrel of lees full fifty yards; it blew down, also, a 

 thick wall, and carried many lighter articles at least 130 yards. {French 

 Journals.) 



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