Mr. W. Brown on the Oscillatio?is of the Barometer. 261 



south wind progresses towards south-east. This is shown by 

 the data, together with the report of the ship Blanche, whose 

 log is given; for on the 17th (a.m.) she was in lat. 31° 42', 

 long. 76° 59', with " fresh breezes and squally " from south by 

 west, but at this time the hurricane was " off' the Capes of Vir- 

 ginia in lat. 36° 20', long. 74° 2';" again, " off Nantucket 

 Shoals (lat. 41° 5', long. 70°) the gale commenced at 8 p.m. of 

 the 17th," and "off" Nantucket, in lat. 38° 15', long. 67° 30', 

 on the night of the 17th; also early on the 18th, in lat. 

 39° 51', long. 69°." 



18. It is obvious that the foregoing results, if correct, ought 

 to enable us to explain the mode of veering of the wind, and so 

 in great measure they will ; and when they are defective, the 

 want arises from our ignorance of the circumstances imme- 

 diately contingent on the descent of the upper current. If air 

 simply descends upon the north-east current, or meets it from 

 a position on the south, it is evident that whether it changes 

 towards west or towards south of east, will depend on the 

 degree of easterly deflection the north wind has attained ; 

 hence, if the north wind be blowing briskly, the change would 

 probably be towards south of east ; and if feebly, towards 

 west. Also, if a station upon which the north-east wind is 

 blowing receive a south wind approaching it as the line A D 

 (fig. 2), it is obvious that it could not change to north-west 

 and then to south-west, for the air sweeping along the surface 

 in the direction of D A would gradually draw the air adjacent 

 to it into its own direction ; consequently the wind would 

 change first to south-east. Now this change does generally 

 occur, but not always ; for on the 7th and 8th of the month 

 chosen for these observations, the wind changed from north- 

 east to north-west, and blowing in that direction some 

 time, afterwards changed to south-west on the arrival of a 

 storm moving like that of fig. 2. From this therefore we 

 may infer, that portions of the upper current were already 

 descending when it arrived in full force as a south-west storm. 

 The change of the wind from south to north, however, is not 

 so much dependent on circumstances. The position of the 

 line A C, fig. 3, which must always exist with more or less 

 inclination to the direction of the storm or D A, fig. 2, and 

 C D B, fig. 3 (its peculiar effect in the case of § 1 6 being oc- 

 casioned by the peculiarity in the distribution of the pressure 

 of the atmosphere on the line C D), determines it in this 

 case ; thus we find that in the southern and western portions 

 of the locality of a south wind, the south wind first changes 

 to north-west ; but as the north-east wind advances from the 

 northern verge of the storm or wind, it changes again to 



