THE CURRENTS OF THE ATLANTIC. 



will be noted, also, that the most sudden bending of these curves 

 takes place in the neighbourhood of the British Islands, the 

 greatest deviation from the parallels of latitude being in, or near, 

 the meridian of London. And, in accordance with this, London 

 has the same mean temperature as Philadelphia, although it is 

 11^ nearer to the Pole ; while Trondjhem, in Norway, has the 

 same mean temperature as Halifax, notwithstanding the difference 

 of 19 in latitude. 



What has been just said relates to the mean temperature of the. 

 >/ear ; but the influence of the Gulf-Stream is much greater upon 

 the temperature of winter. Thus the winter temperature of Dublin 

 is considerably higher than that of Milan ; and Stromness, in 

 the Orkneys, has a winter temperature greater than that of 

 Paris. In fact, the isothermal line for January, which passes 

 through the Shetland Islands, runs almost exactly from north to 

 xouth ; and thus the winter temperature is nearly the same along 

 the whole eastern coast of Great Britain, while it increases as we 

 proceed from that coast to the westward. In Norway the effect is 

 even more remarkable. Owing to the interposition of the British 

 Islands, the Gulf-Stream is intercepted from the southern portion 

 of the Norwegian coast, while it reaches the northern. The 

 southern limit of the stream thus falls on the town of Bergen ; 

 and accordingly, in winter, the temperature actually increases in 

 proceeding northicard from that point. 



But the disturbing effect of local causes on the temperature is 

 measured exactly by the method employed by Professor Dove. 

 In this method the mean temperature, corresponding to any 

 parallel of latitude, is deduced from the observed temperatures 

 at 36 equidistant points on the parallel, and is regarded as th 

 normal temperature of all places on that parallel ; and the difference 

 between this, and the actual temperature of the place, is obviously 

 u measure of the local influence. This difference is called by 

 Professor Dove the thermic anomaly. We thus find that the 

 measure of the influence of the Gulf-Stream, or the thermic 

 anomaly, at the Orkneys is, on the mean of the entire year, 15 ; 

 while, in the month of January, it amounts to 34. The excess 

 of the actual above the normal temperature is greatest between 

 Jan Meyen and the Lofoden Islands, a little above the Arctic 

 Circle. The mean thermic anomaly is there 22'5 ; while, in the 

 month of January, it amounts to 45. 



