242 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
as they come down from the Arctic Ocean through Davis's Straits, 
press upon the warm waters of the Gulf Stream, and curve then' 
channel into a horse-shoe. Navigators have often been struck 
with the great and sudden changes in the temperature of the wa- 
ter hereabouts. In the course of a single day's sail in this part 
of the ocean, changes of 15°, or 20°, and even of 30°, have been 
observed to take place in the temperature of the sea. The cause 
has puzzled navigators long, but how obvious is it not now made to 
appear ! This " bend" is the great receptacle of the icebergs which 
drift down from the north ; covering frequently an area of hund- 
reds of miles in extent, its waters differ as much as 20°, 25°, and 
in rare cases even as much as 30° of temperature from those about 
it. Its shape and place are variable. Sometimes it is like a pen- 
insula, or tongue of cold water projected far down into the waters 
of the Gulf Stream, Sometimes the meridian upon which it is 
inserted into these is to the east of 40°, sometimes to the west 
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. 
523. These isothermal lines of 50°, 60°, 70°, 80°, &c., 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. 
524. 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 first place, the plate rep- 
