144 THE PHYSICAL GEOGRAPHY OF THE SEA. 
during my researches connected with the wind and current charts, 
and the result has satisfied me that it is neither a dangerous nor a 
constant current, notwithstanding older writers, Horsburgh, -in 
his East India Directory, cautions navigators against it ; and Keith 
Johnston, in his grand Physical Atlas, published in 1848, thus 
speaks of it : 
" This current greatly impedes the progress of those vessels 
which cross the equator west of 23° west longitude, impelhng 
them beyond Cape St. Roque, when they are drawn toward the 
northern coast of Brazil, and can not regain their course till after 
weeks or months of delay and exertion." 
So far from this being the case, my researches abundantly prove 
that vessels which cross the equator five hundred miles to the west 
of longitude 23° west have no difficulty on account of this current 
in clearing that cape. I receive almost daily the abstract logs of 
vessels that cross the equator west of 30° west, and in three days 
from that crossing they are generally clear of that cape. A few 
of them report the current in their favor ; most of them experience 
no current at all ; but, now and then, some do find a current set- 
ting to the northward and westward, and operating against them 
at the rate of twenty miles a day. The inter-tropical regions of 
the Atlantic, like those of the other oceans 270), abound with 
conflicting currents, which no researches yet have enabled the 
mariner to unravel so that he may at all times know where they are 
and tell how they run, in order that the navigator may be certain 
of their help when favorable, or sure of avoiding them if adverse. 
277. I may here remark, that there seems to be a larger flow 
of polar waters into the Atlantic than of other waters from it, and 
I can not account for the preservation of the equilibrium of this 
ocean by any other hypothesis than that which calls in the aid of 
under currents. They, I have no doubt, bear an important part 
in the system of oceanic circulation. 
Admiral Sir Francis Beaufort, the venerable hydrographer of 
England, made, when in command of her Britannic majesty's 
frigate Frederiksteen, in the Mediterranean, some interesting ex- 
periments upon under currents, which I should be glad to see re- 
peated in other parts of the sea, especially between the tropics, in 
the Atlantic, Pacific, and Indian Oceans, and wherever the water 
is remarkably transparent. That officer says : 
