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XXVII. On the Storms of Tropical Latitudes. By William 

 Brown, Jim,* 



THE intention of this paper is to show that the explana- 

 tion given in my essay on the " Oscillations of the Ba- 

 rometer," inserted in this Magazine of June 1842, of the de- 

 scent of the barometer during the south-west storms of high 

 latitudes, and its subsequent ascent as the storm changes to 

 north, may be extended to the phaenomena presented by the 

 hurricanes of tropical latitudes, and that it may be generalized 

 as follows : — All winds, of whatever force, which depress the 

 barometer in any considerable degree, are caused by the de- 

 scent of the upper current of the atmosphere. The velocity 

 or momentum which this current has acquired in flowing from 

 higher columns of the atmosphere to lower, causes it, instead 

 of changing its course to that of the lower one, to flow along 

 the surface of the earth in its original direction, in the place 

 of the opposite or lower current of heavy air, which is neces- 

 sary to maintain the ordinary pressure of the atmosphere. A 

 diminution or rarefaction of the air is consequently produced, 

 which increases until the force of the current is spent or is 

 unequal to the opposite force, that of greater density, which 

 then impels the air to flow towards the rarefied atmosphere 

 occupying the locality of the storm, and restores it to its 

 former density and pressuref. 



These forces act in the direction of the meridian, but the 

 force and direction of the wind are compounded of these 

 forces and those produced by the rotation of the earth. 



Further, a rarefaction of the air produced at any station A 

 by the flow of the air towards another B, causes fresh por- 

 tions of the upper current to descend behind A, and pro- 

 duces a constant recession of the storm, which, when modi- 

 fied by the rotation of the earth, occasions the progressive 

 movement of hurricanes. 



As these views, however, are opposed to opinions already 

 advanced on this subject, it will be necessary before proceed- 

 ing further to examine their foundation. 



* Communicated by the Author. 



f In the calculations then given in illustration, for the sake of obtaining 

 data for the calculation of the extent of the depression of the barometer 

 to which it might be reduced by this cause, I have limited the depression 

 to the time when the actual height of the atmospheric column, or in other 

 words the elasticity of its uppermost portions, is reduced to that of the 

 colder columns towards which the upper current is flowing. It is obvious, 

 however, that the only limit to the diminution of pressure is the destruc- 

 tion of the momentum of this current by the resistance opposed to it ; and 

 this, as is evidently the case, between the tropics and probably in high 

 latitudes also, may not take place until the height of the column has been 

 reduced much below this. 



