Your milk is brought to you in a china mug. Then go to the store-room (if there is no store-room in your house go to the nearest Delicatessen store). You will see how all the things which we are supposed to eat tomorrow and next week and next year have been put away in jars and cans and other artificial containers which Nature did not provide for us but which man was forced to invent and perfect before he could be assured of his regular meals all the year around. Even a gas-tank is nothing but a large pitcher, made of iron because iron does not break as easily as china and is less porous than clay. So are barrels and bottles and pots and pans. They all serve the same purpose--of providing us in the future with those things of which we happen to have an abundance at the present moment. And because he could preserve eatable things for the day of need, man began to raise vegetables and grain and saved the surplus for future consumption. This explains why, during the late Stone Age, we find the first wheat-fields and the first gardens, grouped around the settlements of the early pile-dwellers. It also tells us why man gave up his habit of wandering and settled down in one fixed spot where he raised his children until the day of his death when he was decently buried among his own people. [Illustration: PREHISTORIC MAN IS DISCOVERED.] It is safe to say that these earliest ancestors of ours would have given up the ways of savages of their own accord if they had been left to their fate. But suddenly there was an end to their isolation. Prehistoric man was discovered. A traveler from the unknown south-land who had dared to cross the turbulent sea and the forbidding mountain passes had found his way to the wild people of Central Europe. On his back he carried a pack. When he had spread his wares before the gaping curiosity of the bewildered natives, their eyes beheld wonders of which their minds had never dared to dream. They saw bronze hammers and axes and tools made of iron and helmets made of copper and beautiful ornaments consisting of a strangely colored substance which the foreign visitor called "glass." And overnight the Age of Stone came to an end. It was replaced by a new civilization which had discarded wooden and stone implements centuries before and had laid the foundations for that "Age of Metal" which has endured until our own day. It is of this new civilization that I shall tell you in the rest of my book and if you do not mind, we shall leave the northern continent for a couple of thousand years and pay a visit to Egypt and to western Asia. "But," you will say, "this is not fair. You promise to tell us about prehistoric man and then, just when the story is going to be interesting, you close the chapter and you jump to another part of the world and we must jump with you whether we like it or not." I know. It does not seem the right thing to do. Unfortunately, history is not at all like mathematics.