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



position of the sun ; but in one very material circumstance the 

 regions about the equator are subject to a variation to which 

 temperate regions are not exposed ; this is the alternate north 

 and south declination of the sun, occasioning at some periods 

 of the year a partial or entire reversal of the regular currents 

 of the atmosphere, and thus producing the apparent disparity 

 between the storms of temperate and tropical latitudes. 



The facts which may be considered as established regard- 

 ing hurricanes within the tropics are the following : the wind, 

 at the onset of the storm usually blows from north-east, ge- 

 nerally more easterly than the trade-wind, and sometimes from 

 north or north-west. After blowing some time a calm fre- 

 quently ensues, after which the wind again blows as violently 

 as before, but from south-east or south-west. On the east side 

 of the storm the wind veers from north to south (sometimes 

 without the intervention of a calm) by east, but on the western 

 side frequently if not always by west. The barometer falls 

 during the first part of the storm, and rises again with the 

 second part. Hurricanes commencing about the 10th or 15th 

 degrees of latitude, advance in a curve somewhat of a para- 

 bolic form, from east-south-east to west-north-west, until about 

 the 30th degree of latitude, when their direction gradually 

 changes towards east ; and they then advance towards north- 

 north-east or north-east until latitude 40° or 45°. 



I have not thought it necessary to adduce any particular 

 instances in support of these facts; they are well established by 

 the observations of Red field and Reid, and are those upon 

 which the theory advocated by them is founded. 



Now storms of high latitudes in like manner consist of two 

 portions, but the first is from south or south-west, which de- 

 presses the barometer, and the second from north-west or north- 

 east, which restores it to its former elevation ; a calm or lull 

 frequently intervening between them. Thus the same de- 

 scription applies to storms of both regions if we change the 

 directions of the wind, they being exactly opposite. 



Hence then if storms arise from the descent of the upper 

 current of the atmosphere, its direction during tropical hur- 

 ricanes must be the reverse of its general course ; and it will 

 appear from a consideration of the following facts that we 

 have a right to infe* that this is the case. 



Whilst storms of high latitudes are most frequent and vio- 

 lent in winter, those of the tropics occur only during summer ; 

 thus of nine gales whose courses Redfield has tracked out 

 on a chart inserted in vol. xxxi. of the American Journal of 

 Science, one occurred in June, five in August, and three in 

 September; in conformity therefore with general opinion, 



