NOETH-EASTEELY SET TO WESTEEN EUEOPE, ETC. 429 



57° in January and 61° in August. Between this bed and the Irish coast 

 the temperature is more uniform ; there is, however, in the middle of this 

 distance, in about longitude 25° West of Greenwich, a belt of water of a 

 decidedly higher temperature." 



(422.) What has just been quoted refers to the S.W. coasts ; carrying 

 the views farther Northward, there is a very important meteorological 

 paper of Mr. Alexander Buchan, Secretary to the Meteorological Society, 

 " On the Temperature of the Sea on the Coast of Scotland," based on ob- 

 servations carefully collected from numerous stations, between January, 

 1856, and 1865, and the one great fact elicited is given as follows: — 



The great excess of the temperature of the sea over that of the air in the 

 North is perhaps the most remarkable fact in the meteorology of Scotland. 

 It is a difference, moreover, as the following Table will show, which may 

 be considered constant from year to year : — 



This Table teaches, if examined closely, the slowness with which changes 

 in temperature of the air are completely propagated through the waters of 

 the Ocean, in those Northern parts where the power of the sun's rays is 

 greatly diminished. 



When the tendency of the temperature of the sea to follow that of the 

 air is considered, it can scarcely admit of a doubt that, if the waters of the 

 sea were stationary round Orkney from year to year, their temperature 

 would ultimately fall to that of the air, or at least to within about half a 

 degree of it. But this is not the case ; there is some influence at work 

 keeping the temperature of the sea 3° above that of the incumbent air. 

 The enormous amount of heat sufficient to maintain the whole waters of 

 the sea in the North from 2° to 3° above the air, must be brought from 

 warmer latitudes by currents of some sort or other. Since, then, a sea 

 current from the South must be conceded, what is the agent employed? 



(423.) Hitherto we have referred but very slightly to the movements or 

 temperature of the lower strata of the Ocean waters, but this very wide 

 question has a most important bearing on our present subject. The very 

 important investigations which were carried on in H.M. Ships Lightning 

 and Porcupine, under the superintendence of Dr. Carpenter and Mr. Gwyn 

 Jefferys, will be adverted to in a special section at the end of this book ; 

 but, as connected with this portion of our subject, it may be stated that 

 the voyage of the Porcupine, in 1869, demonstrated that there was a 

 stream of warmer water, 900 fathoms deep, between Iceland and Spain, 

 and equally as much near Eockall Bank. Between the latter and the 

 Fseroe Islands it reaches to the bottom, or a depth of 767 fathoms, and at 

 this the temperature is 41-6°. 



