TEMPEEATURE OF THE OCEAN. 



641 



entrance of Baffin's Bay, and then keep a course of general parallelism to 

 the coast of Greenland, crossing the meridian of 30° W. at almost equal 

 intervals. The Winter Isotherm of 45^° follows almost exactly the course 

 of the Summer Isotherm of 54^° as far as the Shetland Islands ; but it 

 then turns back on itself so as to form a loop, passing southwards along 

 the Western Hebrides towards Belfast. The course of the Winter Isotherm 

 of 40°, in like manner, at first bears a general correspondence with that of 

 the Summer Isotherm of 50°, skirting the South coast of Iceland, and then 

 passing N.E. in the channel between Iceland and Norway ; but in lat. 67^° 

 it also returns in a loop, which brings it back to the East coast of Scotland. 

 The Winter Isotherm of 36^°, again, corresponds very closely with the 

 Summer Isotherm of 45° ; passing through Iceland, and then keeping a 

 N.E. course which carries it far to the North and East of the North Cape, 

 when it, too, forms a loop, bringing it back to the coast of Russian Lapland. 

 Finally, the Winter Isotherm of 32° proceeds along a similar course from 

 the Banks of Newfoundland to the northernmost point of Iceland, and then 

 onwards towards Jan Mayen. 



In the above, it will be remarked that the Surface Temperature, North 

 of 40° N., is much greater on the eastern than on the western side of the 

 Atlantic, both in summer and winter ; this is due in a great measure to 

 the prevalent south-westerly winds, blowing the warmer water in a north- 

 easterly direction, and also, as will be hereafter explained, to the general 

 oceanic circulation. 



It is beyond the scope of this work to enter more into detail as to the 

 power of the various Surface Currents in distributing heat over the Ocean ; 

 but that this heated water does not extend to any great depth will be 

 understood from the following remarks on Sub-surface Temperatures. 

 We must also refer the reader to the earlier portion of this book, where, 

 in the description of the Currents, especially of the Gulf Stream, some 

 particulars of the depth to which their warm water extends is generaUy 

 given. 



Sub-surface Temperature. — Taking a general view, or mean for the year, 

 of the water in mid-Atlantic, in a section taken nearly North and South, 

 we find the Temperatures (Fahr.) as follow : — 



CO 



00 



CO 



At the Stirface .. 



„ 50 fathoms 



., 100 



„ 200 



„ 600 „ 



„ 1000 



n 2000 



Bottom 



Depth of bottom 



54 

 53 

 62 

 45 

 37 

 36 

 34 

 33 



2200 

 fms. 



It may now be confidently stated as a general fact, (1) that over not 

 N. A. 0. 82 



