306 THE PHYSICAL GEOGRAPHY OF THE SEA. 



of 50° longitude. By its discovery we have clearly unmasked 

 the very seat of that agent which produces the Newfoundland fogs. 

 It is spread out over an area frequently embracing several thou- 

 sand square miles in extent, covered with cold water, and sur- 

 rounded on three sides, at least, with an immense body of warm. 

 May it not be that the proximity to each other of these two very 

 unequally heated surfaces out upon the ocean would be attended 

 by atmospherical phenomena not unlike those of the land and sea 

 breezes ? These warm currents of the sea are powerful meteoro- 

 logical agents. I have been enabled to trace, in thunder and light- 

 ning, the influence of the Gulf Stream In the eastern half of the 

 Atlantic, as far north as the parallel of 55° north ; for there, in 

 the dead of winter, a thunder-storm is not unusual. 



885. These isothermal lines of 50°, 60°, 70°, 80°, etc., may 

 illustrate for us the manner in which the climates. in the ocean are 

 regulated. Like the sun in the ecliptic, they travel up and down 

 the sea in declination, and serve the monsters of the deep for signs 

 and for seasons. 



886. It should be borne in mind that the lines of separation, as 

 drawn on Plate IX., between the cool and warm waters, or, more 

 properly speaking, between the channels representing the great 

 polar and equatorial flux and reflux, are not so sharp in nature as 

 this plate would represent them. In the flrst place, the plate rep- 

 resents the mean or average limits of these constant flows — polar 

 and equatorial ; whereas, with almost every wind that blows, and 

 at every change of season, the line of meeting between their wa- 

 ters is shifted. In the next place, this line of meeting is drawn 

 with a free hand on the plate, as if to represent an average ; 

 whereas there is reason to believe that this line in nature is vari- 

 able and unstable as to position, and as to shape rough and jag- 

 ged, and oftentimes deeply articulated. In the sea, the line of 

 meeting between w^aters of diflbrent temperatures and density is 

 not unlike the sutures of the skull-bone on a grand scale — very 

 rough and jagged ; but on the plate it is a line drawn with a free 

 hand, for the purpose of showing the general direction and po- 

 sition of the channels in the sea, through which its great polar and 

 equatorial circulation is carried on. 



