As imaginative children personify the sounds they hear, so the men and women of an early time personified everything that lived or moved or gave any sign of life. They filled the earth, air, and sea with imaginary beings who had power over the elements and affected the lives of men. There were nymphs in the sea, dryads in the trees, kindly or destructive spirits in the air, household gods who watched over the home, and greater gods who managed the affairs of the world. When an intelligent man finds himself in new surroundings, he begins at once to study them and try to understand them. In every age this has been one of the greatest objects of interest to men, and every generation has endeavoured to explain the world, so as to satisfy not only its curiosity but its reason. The myths were explanations of the world created by people who had not had time to study that world closely nor to train themselves to study it in a scientific way. They saw the world with their imaginations quite as much as with their eyes, and as they put persons behind every kind and form of life, they told stories about the world instead of making accurate and matter-of-fact reports of it. The change of the seasons is not at all mysterious to us; but to the Norsemen it was a wonderful struggle between gods and giants. In the summer the gods had their triumph, but in the winter the giants had their way. Year after year and century after century this terrible warfare went on until a day should come when, in a last great battle, both gods and giants would be destroyed and a new heaven and earth arise. These same brave and warlike men believed that the most powerful fighter among the gods was Thor, and that it was the swinging and crashing of his terrible hammer which made the lightning and thunder.