1872.] 



{ Shearwater 3 Scientific Researches. 



631 



the summer heat and the winter cold. — It would probably be found, how- 

 ever, on a more detailed comparison, that even in winter the relative tem- 

 peratures of the Sea and Air are much influenced by the direction of the 

 Wind ; as the greatest differences may be expected to present themselves 

 when, after a continuance of S.W. winds which have produced a powerful 

 drift of warmer water towards the coast *, the wind changes to the N.E., 

 immediately reducing the temperature of the Air, and not for some time 

 producing a like fall in that of the Sea. 



154. It is further urged by Mr. Buchan, who has paid special attention 

 to the Distribution of Temperature in the British Islands j* , that the pecu- 

 liar course of the Isocheimal lines, or lines of mean Winter temperature, 

 indicates that the ameliorating influence comes from the west, rather than 

 from the south-west, and thus from the Sea as well as from the Air. The 

 course of the Isotherms between the months of April and October has a 

 general relation to the parallels of latitude ; the summer-temperatures of 

 Ireland and the West Coast being, however, lower in August (Plate VI.) 

 than those of the middle of England, showing that the neighbourhood of 

 the sea has a reducing effect at that period. In November, however, the 

 direction of the Isotherms begins to undergo a marked change ; their 

 western portions turning northward, and their eastern portions southward, 

 whilst the intermediate parts run almost due north and south. Thus the 

 Isotherm of 43° passes from Belfast across the Irish Sea to Whitehaven, 

 and then turns southwards through Lancaster to Oxford ; while that of 45°, 

 after passing Cape Clear and Wexford towards Anglesea, there takes a 

 direct southward bend which carries it to Exeter. This meridional direc- 

 tion shows itself still more strongly in December, — the line of 42°, which 

 passes through Belfast, turning southwards so as to pass through Liverpool 

 and Bristol, and th°nce S.E. to Brighton and Dieppe ; while the line of 41° 

 ranges nearly north and south from the Shetland and Orkney Islands to 

 Dover, and that of 40° runs parallel to it from the Moray Firth to Cromer. 

 It is in January, however, that this Meridional direction is most pronounced 

 (Plate VI.), — the Isotherm of 39° passing from Unst along the Western 

 coast of Scotland, and then through the centre of England to Hastings ; 

 and the Isotherms of 38° and 37° lying parallel to it on the east, while 

 those of 40° and 41° show a like parallelism to it on the west. In Ireland 

 the Isocheimals "seem to envelope the island with their folds, which in* 

 crease in warmth from the centre of the island outward to the ocean." 

 In February, however, the influence of the sun begins to show itself in the 

 tendency of the Isotherms to exchange their meridional direction for that 

 of the parallels of Latitude ; and this is still more marked in the March 

 Isotherm, that of April showing the change completed. Now, as Mr. 



* 1 learn from a friend who resides at Sidmouth, that the Sea-temperature always 

 sensibly rises there with a S.W. gale. 



f "The Temperature of the British Islands," in Journal of the Scottish Meteorolo- 

 gical Society, vol. iii. 1871, p. 102, 



VOL. XX. 2 z 



