Mr. W. Brown on the Storms of Tropical Latitudes. 213 



August being usually said to be the month of hurricanes. 

 Now the sun is at this time in the northern hemisphere, and 

 the month of August is frequently that in which the tempera- 

 ture of the portion of this hemisphere north of the tropics is 

 the highest; and although the trade-wind is still maintained, 

 the breadth of its zone is much diminished, its southern verge 

 retiring many degrees from the equator. We are, therefore, 

 fully justified in supposing that the air of the regions about 

 the tropic may become for a time so much warmer than 

 that nearer the equator, as to reverse the usual relation of 

 the heights of the atmospheric columns, and consequently the 

 direction of the upper current, which now flows from north 

 to south; although the lower strata of the air are apparently 

 unaffected by it until the descent of this current to the sur- 

 face of the earth. But we find also that Redfield and Reid 

 have fully succeeded in identifying the West India hurricanes 

 with the typhoons of the Chinese Sea and India Ocean, which 

 set in from north, and occur at the same time of the year, 

 that is, when the south-west monsoon is blowing; when of 

 course the direction of the upper current being from north- 

 east, or the opposite of the monsoon, is actually that of the 

 onset of the storm, thus affording almost proof of the truth of 

 the inference. 



Let us suppose then that, in accordance with the views here 

 advanced, the upper or northerly current falls with the velo- 

 city of a hurricane between B and C, places on the same 

 meridian ; the air rushes from B to C with the force given by 

 its momentum without 

 being replaced, causing Fig. 1. 



a rarefaction of the air at A—*— B — * C 



B, and consequently a di- N. ■ S. 



minution of its pressure ; 



this rarefaction increases with the continuance of the storm 

 until the force of the wind is overcome ; when, after the inter- 

 val of a calm caused by the balancing of opposite forces, the 

 density of the air south of C prevails and causes it to rush 

 back, as into a partial vacuum, to restore the former density 

 and pressure ; the barometer now rising until the cessation of 

 the hurricane. But whilst this is going on in the space be- 

 tween B and C, it is evident that the air being so rarefied at B 

 will cause a flow towards it from north ; and fresh portions of 

 the upper current will descend on the north of B. Thus whilst 

 the south wind or last portion of the hurricane is blowing from 

 C towards B, the north wind or first portion is blowing from A 

 towards B, as is indicated by the arrows ; and the barometer 

 is rising between B and C and falling between A and B ; and 



