Professor Mitchell wi the Trade- Winds. '%Q 



of the air of the equatorial regions towards the pole, but of a gy- 

 ratory movement in a vertical plane. *^ 



(c) On Monday the 17th April 1812, the SoufFrier mountain 

 on the island of St Vincent, after having remained dormant for 

 more than a century, suddenly emitted a column of smoke, 

 which continued to increase in magnitude and density until 

 Thursday the 30th, when it was accompanied with an appear- 

 ance of flames and eruption of lava. On Friday the 1st of 

 May, the atmosphere of Barbadoes was darkened by clouds of 

 volcanic sand and ashes, which descended upon the island to the 

 depth of nearly three quarters of an inch. Barbadoes hes at 

 the distance of from 90 to 100 miles east of St Vincent, and 

 the trade-winds blow so directly and violently from the former 

 towards the latter island, that a passage from St Vincent to 

 Barbadoes can be effected only by making a circuit of many 

 hundred miles. Von Buch remarks, that " by this striking 

 occurrence, the returning current in the upper regions was prov- 

 ed, and with it the theory of the trade-winds, for which we are 

 indebted to Hadley, was become something more than conjecture. 



It places the existence of the upper current beyond the reach 

 of a doubt, but lends probability to the theory of Hal ley rather 

 than to that of Hadley, which last supposes the upper current 

 to be directed from the equator towards the poles. In the pre- 

 sent instance its course was due east. It is well known that the 

 under current is deflected from its course by islands and projecti- 

 ing shores, but it is not easy to see why Hadley 's upper current 

 should be similarly affected. I cannot help suspecting that a 

 vortex had established itself with one extremity on Barbadoes, 

 and the other on St Vincent, and that the ashes were whirled 

 into the air at the latter or western extremity, and brought down 

 to the surface at the eastern *. 



{d) " On the western coasts of both continents, a wind from 

 the west prevails.'* i* This passage is quoted from a work which, 

 along with much valuable matter, contains a share of inconclu- 

 sive argument from facts incorrectly stated. These westerly 

 winds are created by a cause, having a close resemblance to that 

 to which the trade- winds are ascribed by Halley. They are un- 



• See for the above facts Von Buch, in loc. cit. and Philosophical Maga- 

 zine, vol. ix. 

 t Daniell's Meteorological Essays. 



