In spite of its great size the whale is so perfectly adapted to its surroundings that it is a highly active animal. It swims without apparent effort and on account of the great strength of the enormous horizontal tail fin, it can jerk itself above the water and take long leaps. The smoothness of the skin facilitates the passage of the immense bulk through the water and the thick layer of fat diminishes the weight so that a whale can move with the rapidity of a steamship. The Greenland Whale is, on the whole, an amiable animal. It seems to prefer to live at peace with its kind, and although it can make great havoc with its immense tail fin, it seemingly does so by accident rather than from viciousness. Like all other animals the whale has its enemies, especially when young. The killer-whale and some sharks hunt and attack the young whales, as indeed they do the older ones; but the greatest enemy of all is man. For a thousand years he has systematically pursued and captured many species, until some are nearly exterminated. The Americans became great whale hunters in the nineteenth century, and in the thirty-eight years from 1835 to 1872 nearly 20,000 ships engaged in this industry. These whaling ships were fitted especially for this work. They were built to withstand the perils of the ice-bound northern seas and were arranged for long voyages. It was a sad day in the coast villages when the whalers sailed on these long, perilous and uncertain cruises, for the ships frequently were gone three years and some never came back, though as a whole the actual loss of human life was comparatively small. A number of ships would if possible keep sufficiently near together to render assistance in case of accident.