856 Meteorological and Hydrographical 



perience testifies ; but there is no evidence that most, or, in- 

 deed, many of these, come from the West Indies ; on the con- 

 trary, there is every reason to conclude, not only that they are 

 produced along the polar margin of the stream, but that the 

 greater part of those experienced in the Northern Atlantic, and 

 in this country, originate in the same place. 



In Table II. it will be found that the temperature of the sea 

 fell 5-6, between lat. 40° 25' N. and 42° 40' ; while, on either 

 side, the progressive changes of temperature were much more 

 gradual. The observations of Mr Battersby, noticed above, 

 give even a greater change. Thus, on Sept. 21. 1841, in lat. 

 44° 16' N., long. 34° W., the temperature of the sui-face was 

 70°-8 ; and the following day, in lat. 45° 4', and long. 31° 10', 

 it was only 62^-1 ; while, on eitlier side, the changes were 

 small and tolerably regular. Observations in the eastern part 

 of the Atlantic, too, from the Azores towards the Lizard, shew 

 a rapid change in the temperature of the water, a little to the 

 northward of the former. Thus, if a line be drawn across the 

 Atlantic, from the southern part of the banks of Newfound- 

 land to Cape Finisterre, it will nearly indicate the division 

 between the colder and warmer waters of the Atlantic. The 

 position of the line varies at different seasons of the year, but 

 that mentioned is sufficiently near for general purposes. 



As the mean temperature of the air over the open sea is 

 generally somewhat under that of the surface water, the tem- 

 perature of the air to the north of the line above mentioned 

 must generally be considerably less than that of the air to the 

 south of it. Now, it is clear that there never can be a state of 

 equilibrium between two masses of air, so different in tempe- 

 rature, placed so close together, but a current of cold air would 

 flow to the south of the line from the north, while the warmer 

 air would rise in the atmosphere, and flow off to the north, 

 above the lower and cooler currents, precisely as is the case 

 with the trade-Aviuc'S, only, the difference of temperature of 

 the two currents being greater, the resulting currents will be 

 more violent while they last, and less regular in their appear- 

 ance. 



On referring to Table II. such will be found to have actually 

 occurred. Thus, on Feb. 24, at 3 P.M., the wind was SSW., 



