TRANSACTIONS OF THE SECTIONS. 19 



the English Channel, of about three-quarters of a degree for each degree of latitude 

 southward in winter, and a change of about a degree of surface temperature for each 

 degree of latitude in summer. 



In regard to the effects of season (taking the average) within the same portion of 

 the transatlantic passage, there appears to be a range of 9° or 10° ; the highest being 

 about 61° in July and August, and the lowest 51° to 52° in January and February. 

 The analyses of the observations on the various passages yielded, as to changes in the 

 surface temperature, betwixt 12° and 30° W., something like the following series :■ — 



Jan. 52 Feb. 52 March 52-8 



April 53-8 May 56 June 59 



July 61 August 61 Sept. 60 



Oct. 59 Nov. 55 Dec. 53 



The atmospheric changes for the same range of ocean may thus, perhaps, be 

 proximately represented : — 



Jan. 43 Feb. 45-5 March 47-5 



April 51 May 56 June 59-5 



July 63 August 61 Sept. p8 



Oct. 54 Nov. 50 Dec. 45-5 



In specifying the general results of all the observations on the oceanic temperature, 

 we find the first and leading fact to be, a division of the transatlantic belt into two 

 characteristic portions of nearly equal extent, differing, in a striking and singular 

 manner, both in their ordinary temperatures, their extremes, and their changes. ^ 



Thus for nearly half the passage across from England, that is, as far as longitude 

 38° W., in a W. by S. direction, the surface temperature was not found to descend 

 below 50° even in the winter passages, nor to rise in any part of the year (as far as 

 the observations go) higher than 66°. But on reaching 42° W. a temperature of 44° 

 was met with, and at 48° to 50° W. longitude a minimum of 32° was not uncom- 

 mon, with a maximum sometimes reaching to 69°. Further west, in 58° to 60° 

 longitude (the mean latitude being about 42° N.), along with a minimum tempera- 

 ture ranging from 32° to 42°, a maximum was found as high as 74°. From this 

 meridian to 72° W. similar differences of temperature, except near the American 

 coast, were found to be prevalent. 



In regard to mean differences of the extremes of temperature, taking the averages 

 of all the observations within meridians of 2^ in width, the results are still more 

 striking ; for in the first half of the passage, going westward, we find a meanrange of 

 surface temperature, for each 2° of longitude, of only 11°*3 ; whilst in the western 

 half the mean range extends to 29°'7. Within the first half, too, where the extremes 

 of temperature of the whole section were found to differ only 19°, the difference 

 betwixt the highest and lowest temperature observed in the second or westerly half, 

 reached to 42°. 



This diversity of temperature clearly pointed out the two great and well-known 

 oceanic currents— one from the tropics, the other from the Polar regions — meeting, 

 coalescing, and interlacing within the range of the belt of waters referred to ; the 

 former current yielding an occasional warmth of 20° to 22° above the mean atmo- 

 spheric temperature, and the latter a frequent cold as much below it. 



But the phaenomena may be rendered more intelligible and instructive if we note 

 the appearance and trace the progress of the more marked alternations in sailing 

 from the English Channel westward ; say from longitude 12° W., in the mean latitude 

 of 50° N., to that of 72° W., in the 4 1st parallel. This belt, extending to 60° of 

 longitude, may be conveniently taken in six decimate sections, as represented in 

 Plate I., several of which, it will be seen, afford peculiar and characteristic differ- 

 ences. 



The first three of these decimate sections exhibit, for the most part, a striking 

 uniformity of character ; for as far, at least, as longitude 38° W. no particular in 

 the differences of surface temperature strikes us, except a gradual rising of the means, 

 within two degrees' space, from 52°-9 to 58°'7, during a descent in the mean lati- 

 tude from 50° to 46° N. But in longitude 38° to 42° W. the range of oceanic tem- 



2* 



