sails so nicely trimmed to the breeze? Who pilots them, and what master hand holds the helm? What compass, and of whose workmanship, is that which guides these delicate and graceful little argonauts from sea to sea? Arriving off the "Stormy Capes," the flotilla is separated, one division holding its way for the Pacific, the other hauling up for the Atlantic, each bound on its high and secret mission. They build, equip, and repair as they go; the fleet is imperishable, but individual life in it is ephemeral. They die, these tiny "men o' war," one after another, but the same watchful Providence that cared for them while living, now provides for their burial being dead. The inanimate shell, drawn to distant seas by under currents, descends like autumnal leaves from depth to depth by an insensible fall. In future times the seaman's sounding-rod may reach the bottom on which it has fallen, and thus reveal to man the secret paths of the sea,—or when the geological clock next strikes the hour, the same little shell may, by some throe of nature, be brought up to the surface, and spread out in its marl bed, to fertilize and make fruitful unknown lands.
741. Drift described.—There is a movement of the waters of the ocean which, though it be a translation, yet it does not amount to what is known to the mariner as "current," for our nautical instruments and the art of navigation have not been brought to that state of 'perfection which will enable navigators generally to detect as currents the flow to which I allude as drift. If an object be set afloat in the ocean, as at the equator, it would, in the course of time, even though it should not be caught up by any of the known currents, find its way to the icy barriers about the poles, and again back among the tepid waters of the tropics. Such an object would illustrate the drift of the sea, and by its course would indicate the route which the surface-waters of the sea follow in their general channels of circulation to and fro between the equator and the poles.
742. Plate IX.—The object of Plate IX., therefore, is to illustrate, as far as the present state of my researches enable me to do, the circulation of the ocean as influenced by heat and cold, and to indicate, on one hand, the routes by which the overheated waters of the torrid zone escape to cooler regions, and to point out, on the other, the great channel-ways through which the same waters, after having been deprived of this heat in the extra-tropical or polar regions, return again towards the equator; it
