28 THE PHYSICAL GEOGRAPHY OF THE SEA. 
an inclined plane, whose submarine ascent is not less than ten 
inches to the mile. 
The Niagara is an " immense river descending into a plain." 
But instead of preserving its character in Lake Ontario as a dis- 
tinct and well-defined stream for several hundred miles, it spreads 
itself out, and its waters are immediately lost in those of the lake. 
Why should not the Gulf Stream do the same ? It gradually en- 
larges itself, it is true ; but, instead of mingling with the ocean by 
broad spreading, as the "immense rivers" descending into the 
^ northern lakes do, its waters, like a stream of oil in the ocean, 
preserve a distinctive character for more than three thousand miles. 
11. Moreover, while the Gulf Stream is running to the north 
from its supposed elevated level at the south, there is a cold cur- 
rent coming down from the north ; meeting the warm waters of 
the Gulf midway the ocean, it divides itself, and runs by the side 
of them right back into those very reservoirs at the south, to which 
theory gives an elevation sufficient to send out entirely across the 
Atlantic a jet of warm water said to be more than three thousand 
times greater in volume than the Mississippi River. This current 
from Baffin's Bay has not only no trade-winds to give it a head, 
but the prevailing winds are unfavorable to it, and foi* a great part 
of the way it is below the surface, and far beyond the propelling 
reach of any wind. And there is every reason to believe that this 
polar current is quite equal in volume to the Gulf Stream. Are 
they not the effects of like causes ? If so, what have the trade- 
winds to do with the one more than the other ? 
12. It is a custom often practiced by seafaring people to throw 
a bottle overboard, with a paper, stating the time and place at 
which it is done. In the absence of other information as to cur- 
rents, that afforded by these mute little navigators is of great 
value. They leave no tracks behind them, it is true, and their 
routes can not be ascertained. But knowing where they were 
cast, and seeing where they are found, some idea may be formed 
as to their course. Straight lines may at least be drawn, show- 
ing the shortest distance from the beginning to the end of their 
voyage, with the time elapsed. Captain Beechey, R. N., has pre- 
pared a chart, representing, in this way, the tracks of more than 
one hundred bottles. From it, it appears that the waters from 
every quarter of the Atlantic tend toward the Gulf of Mexico and 
