]869.] between Air-currents and subsequent Weather. 15 



are very generally followed after a brief interval by a serious barometrical 

 depression, frequently resulting in a southerly gale. 



In 12 instances a southerly gale followed in 2 days. 



„ 4 „ „ ,/ „ 3 days. 



„ 6 „ fresh southerly winds, not a gale, followed. 



„ 2 „ a north-east gale followed. 



„ 2 „ a southerly gale set in at once. 



„ 1 „ no change of weather ensued. 



27 



These facts appear to show that the conditions of case I. indicate a 

 deep-seated disturbance of the atmosphere. In almost every case they 

 seem to point to the existence, or at least the formation, of a barometrical 

 minimum over the Atlantic Ocean, which will probably advance to our 

 coasts and result in a southerly storm. On only two occasions did the 

 centre of the disturbance pass to the southward of these islands, viz. 

 the two instances in which the north-easterly gale followed. 



Case II. The polar current flows in a latitude lower than the equatorial 

 current. 



In other words, easterly winds prevail in the south, westerly in the 

 north. 



Thirty instances have been noticed. 



In 1 1 instances no change of weather ensued. 



7 ,, The polar current completely displaced the equatorial 



current over these islands, and easterly winds set in. 

 7 ,, This displacement was only partial, and north-westerly 

 winds set in. 



5 „ Southerly gales or fresh southerly winds followed, 

 30 



It would appear from the foregoing that case II. is not, as a rule, indi- 

 cative of the approach of a serious atmospherical disturbance, although 

 such did occur in five instances (one-sixth of the total number. under 

 consideration). In the great predominance of instances the weather 

 either remained unchanged and calm, or else the polar current succeeded 

 in displacing the equatorial more or less completely, and the winds which 

 prevailed over these islands generally were from points between N.W. and E. 



It is obvious that, from the very limited area from which our obser- 

 vations are derived, we are at present unable to examine into the mutual 

 action of the currents on each other (unaffected by any influence exerted 

 on the wind by inequalities in the earth's surface, such as those produced 

 by an irregular coast-line stretching out into the open sea), as has been 

 done by Mr. Meldrum for the Indian Ocean ; but it is hoped that this 

 commencement of an attempt to trace a connexion between successive 

 conditions of weather may be deemed worthy of the notice of the Royal 

 Society. 



