So mysterious are all the physical of the sea that it is, perhaps, hardly possible to say of any particular one that it is more wonderful than the rest. And yet one is sorely thus to distinguish when upon the movements of the almost inconceivable mass of water which goes to make up that major portion of the external superficies of our planet which we call “the sea.” In spite of all the labours of , notwithstanding all the care and patience which science has upon oceanography, it is nevertheless true that, except in a few broad instances, the direction, the rate, and the dependability of ocean currents still remain a profound mystery. Nor should this excite any wonder. If we remember how great is the influence over the sea by the winds, how slight an in the specific gravity of water is sufficient to disturb its and cause masses hundreds of square miles in area to exchange levels with the surrounding ocean, we shall at once admit that, except in those few instances hinted at which may be referred to constant causes, ocean currents must of necessity be still among the phenomena whose operations cannot be reckoned upon with any certainty, but must be watched for[320] and guarded against with the most jealous care by those who do business in great waters.  
Perhaps one of the commonest of the many errors made in speaking of things is that of confounding current with tide. Now tide, though a variable feature of the circulation of the waters near land, is fairly dependable. That is to say, the navigator may calculate by means of the moon’s age and the of the place not only the time of high water, but knowing the mean height at full and change of the moon, he may and does to what height the water will rise, or how low it will fall at a certain place on a given date. True, a heavy of wind blowing in or against the same direction of the or flowing tide will accelerate or , raise or depress, that tide at the time; but these , though most unpleasant oftentimes to riparian householders, are rarely of much or danger to navigation. This cannot be said of the currents of the sea. The tides have their limits assigned to them both inland and off-shore, although in the latter case it is almost impossible to tell exactly where their influence becomes in the vaster sway of the ocean currents, with all their unforeseen developments. The limits of tidal waters in rivers, on the other hand, being well under observation at all times, may be and are with the greatest exactitude.
 
With regard to the few instances of dependability among ocean currents, the first place will by common consent be given to the[321] Stream. Owing its existence primarily to the revolution of the earth upon its , its outflow through the channel connecting the Gulf of Florida with the North Atlantic is more constant and steady in direction than any ebbing or flowing tide in the world, inasmuch as its “set” is invariably upon one course. Its rate is not so uniform, varying somewhat with the season, but in the narrowest part of the channel remaining fairly constant at about four knots an hour. Yet sail but a few score leagues into the Florida Gulf whence this great river in the sea takes its apparent rise, and its influence disappears! The may seek there in vain for that swift, silent flow which in the Straits of Florida sweeps him north- in the teeth of the strongest gale. What has happened? Does the stream drain into that great land-locked sea by hundreds of channels from the Equatorial regions, but far below the surface, and, obeying some all-compelling impulse, rise to the light upon reaching the Bahama Banks, pouring out its beneficent flood as it comes at the rate of a hundred miles per day? It sweeps into the broad Atlantic, and immediately spreads out into a breadth to which the Amazon is but a , losing its meanwhile, until, having skirted the North American coast as far as the Grand Banks, it rolls in eastward towards these “fortunate .” As it does so the mystery attendant upon it deepens. Its balmy presence cannot be mistaken, for the air on either side of it may be piercing in its keenness,[322] while immediately above it there is summer. A gale blowing at right angles to its course will raise that terrible combination of waves which gives alike to the “Western Ocean” and the “pitch of the ” their evil reputation as the most dangerous in the world; and yet who among navigators has ever been able to determine what, if any, rate of speed it has in mid-Atlantic? Look through hundreds of log-books kept on board ships that are, perhaps, more carefully than any others, the North Atlantic liners, and you shall not find a trace of the Gulf Stream “set” mentioned. In order to make this clear, it should be said that in all properly navigated ships the course and the speed made are carefully throughout the twenty-four hours; and this course, with distance run, calculated from the position by observation of the bodies at the previous noon, gives the ship’s position by “dead reckoning.” The ship’s position being also found by the celestial bodies at the same time, the difference between the latter and the “dead reckoning” position should give the “set” and direction of the current for the twenty-four hours. And in so carefully steered, and whose speed is so a............