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



flowof air from north is still maintained as in the tropical portion 

 of the track of the storm, in every rarefaction it is met by the 

 momentum of the upper current, instead of as before merely 

 by air of greater density; and the directions of the wind are the 

 resultants of the forces of these two currents, the south being 

 generally predominant on the eastern side, and the north on 

 the western: but the latter, which now must ultimately pre- 

 vail to restore the equilibrium of the atmosphere, is always the 

 one which terminates the storm, though still influenced by the 

 descending air, which makes it blow from north-west, and 

 which is still the principal agent in carrying on the storm, 

 giving to its progressive motion an impulse from west. 



The change in the direction of the upper current is indeed 

 conspicuously marked in that of the progressive motion, which, 

 being at first towards west-north-west, gradually becomes less 

 westerly as the impulse from east diminishes, and changes alto- 

 gether from west when the direction of the upper current is com- 

 pletely changed ; hence the approach to a parabolic form of the 

 curve described by the path of the storm, being occasioned 

 by the gradual decrease of the impulse from east, and increase 

 of that from west, whilst the motion towards north remains 

 the same. 



The change in the direction of the wind both at the onset 

 and latter period of the storm, which takes place simul- 

 taneously with the change in that of its progressive motion, 

 appears very clearly from the " data " of the second of these 

 storms, that of August 1830 (Col. Reid's Law of Storms, 

 p. 18) : thus " in latitude 26° 51', longitude 79° 40' in the 

 Florida stream, thegalejwas severe on the 15th from north-north 

 east to south-west." As also "at St. Andrew's (Georgia)," 

 latitude 30° 55', longitude 81° 50', " from 8 o'clock p.m. on 

 the 15th to 2 a.m. on the 16th, the storm was from an eastern 

 quarter, then changed to south-west and blew till 8 a.m." 

 Thus far then the storm preserved its original characters, pro- 

 gressing towards north-west, and terminating with the wind 

 from south ; but at the next station for which the data of the 

 storm are given, both had changed; thus "off Tybee and at 

 Sawannah (Georgia)," latitude 32°, longitude 81°, it began 

 " on the night of the 15th, changed to north-isoest at 9 a.m. 

 on the 16th, and blew till 12 m." 



As the direction of the wind at the onset of the storms of the 

 tropics is the opposite of that of those of high latitudes, so of 

 course the progressive motion of the latter ought to be opposite 

 also, or towards south-east. It is not so easily traced in storms 

 of high latitudes, but what evidence we have goes to show 

 that this is the case. Thus W. C. Redfield says (American 



