So mysterious are all the physical phenomena¹ 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 tempted² thus to distinguish when meditating³ 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 investigators⁴, notwithstanding all the care and patience which science has bestowed⁵ 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 possessed⁶ by the winds, how slight an alteration⁷ in the specific gravity of water is sufficient to disturb its equilibrium⁸ 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.