Mr. W. Brown on the Storms of Tropical Latitudes. 211 



If it be thought that the objections here brought forward 

 are not founded on sufficient observations to amount to a rer 

 futation of this theory, it will at least be allowed, that viewing 

 it in the most favourable light, it remains simply as an hypo- 

 thesis, assumed to account for certain phaenomena, towards 

 proving the truth of which nothing has yet been done, though 

 it is one which is from its nature capable of being tested by 

 an appeal to observation; and therefore in the absence of proof 

 we may ask, how such a whirlwind can be produced and 

 maintained in action whilst advancing over a tract of the 

 earth's surface of three or four thousand miles in length, by 

 the action of the known causes of disturbance to the atmo- 

 sphere ? Whence arises the centripetal force which deflects the 

 air from a rectilinear course ? If indeed the existence of such 

 a whirlwind could be established by direct proof, it would 

 justify the language used by its supporter, " that the long- 

 cherished theory which is founded upon calorific rarefaction, 

 must give place to a more natural system of winds and storms" 

 (American Journal of Science, vol. xxxv. p. 222), although in 

 what way it can be "founded upon the more simple condi- 

 tions of the great law of gravitation " exclusively of the effects 

 of difference of temperature, is by no means easy to conceive. 



Leaving here the consideration of this theory, I may pro- 

 ceed to the development of the proposition with which this 

 pnper commenced ; premising, that as the phaenomena of 

 hurricanes in the two hemispheres have been shown by Col, 

 Reid to correspond with each other, in relation to the position 

 of the equator and the poles, the signs north and south are 

 here used in reference to the northern hemisphere alone ; by 

 which their double signification when applied to meteorolo- 

 gical phaenomena is avoided, and they may be used synony- 

 mously with polar and equatorial. The language may of 

 course in every instance be applied to the southern hemi- 

 sphere by reversing these signs. 



The atmospheric phaenomena within the tropics are ap- 

 parently so much more dependent on general causes than in 

 other regions of the globe, that meteorologists have endea- 

 voured to explain those of the latter, by endeavouring to dis- 

 cover in them some feature, which, though obscured by its 

 association with others, may yet be sufficiently perceptible to 

 characterize them as analogous to phaenomena within the 

 tropics, whose more isolated occurrence has enabled us to 

 refer them to known causes. In the present investigation, 

 however, the reverse is the case ; the reason of which I think 

 will readily appear from the following : — 



The one grand cause of atmospheric changes is the varying 



P2 



