Much light has been thrown on the fact of the existence of under and upper currents in the sea, by the phenomena of the arctic regions, and some of the questions to which these currents give rise are so interesting that we shall treat of them in a new chapter. CHAPTER TWELVE. QUESTION OF AN OPEN SEA ROUND THE POLES--UPPER AND UNDER CURRENTS OF THE OCEAN--CAUSE THEREOF--HABITS OF THE WHALE AS BEARING ON THE QUESTION-- DR. KANE'S DISCOVERY OF AN OPEN SEA IN THE FAR NORTH--NOTES ON THE EXPEDITION--A BEAR-HUNT. It was long and very naturally supposed that the impenetrable ice of the arctic regions extended to, and, as it were, sealed up the pole. But from time to time philosophic observers of Nature's laws began to hint their opinion that there is an open ocean around the pole; and of late years this opinion has all but been converted into a firm belief. Maury remarks, that like air--like the body--the ocean _must_ have a system of circulation for its waters. And an attentive study of the currents of the sea, and a close examination of the laws which govern the movements of the waters in their channels of circulation through the ocean, will lead us irresistibly to the conclusion that always, in summer and winter, there must be, somewhere within the arctic circle, a large body of open water. There is an under-current setting from the Atlantic, northward through Davis' Straits, into the Arctic Ocean, and a surface-current setting out. The fact is proved beyond a doubt by the observations of arctic explorers, who have seen immense icebergs drifting rapidly northward against a strong current. This apparent anomaly could only be accounted for by the fact that a powerful undercurrent carried them northward; and as at least seven times more of these bergs must have been under than above water, we can easily understand how the under-current, acting on the larger mass of each berg, had power to carry it against the surface-current. This under-current is _warm_, while the upper-current is _cold_. Now we know that according to Nature's laws, heated water, like heated air, rises to the surface, and cold water sinks to the bottom. How, then, comes this warm current to be underneath the cold, as soundings have proved it to be? It is owing to the fact that the under-current is much salter, and therefore heavier (despite its warmth), than the surface-current; which latter, being mingled with the drainage and ice-masses of the arctic regions, is comparatively fresh, and therefore light as well as cold.