When man discovered metals, and how to use them, the Stone Age began to draw to a close. There was of course no exact time when the use of stone stopped, and the use of metals began, for in some parts of the world men were using metals for hundreds and even thousands of years, while others, in other countries were still using stone. When Columbus came to America, only a few hundred years ago, the Indians in North America knew nothing of tools or weapons of metal, they were still living in the Stone Age. Another discovery which came about the same time as the use of metals was the art of making glass. Just when men began to use glass we do not of course know, but in some of the most ancient tombs, along with weapons of copper, and ornaments of gold, we find beads and other small objects made of glass. How it came to be discovered is another thing we do not know, or by what race. It is very likely that it was made by many different peoples, at different times in the world's history. Over and over we find that some race which had gone far along the road to civilisation, would be swept away by savage tribes and its discoveries lost for many centuries. We know this, because sometimes we find, when digging in the earth, the remains of savage peoples, with thick skulls and rude weapons, and under these are the skulls and polished weapons and ornaments of a much more highly civilised race. The road which man followed in his progress toward the civilisation we have to-day did not run smoothly upward, like a path up a hill, but dipped up and down and around in many circles, always rising a little higher, however, as the ages went by. It is thought that the sea people first discovered glass. Ordinary glass is made of lime, soda-ash and sand, three very common substances. Because sand is the thing most needed in making glass, we think it must have been discovered by a people living on the seashore. It must have been first made by accident, because man could not have set out to discover something he did not know anything about. The most common story about the first glass is that it was made by some sailors belonging to the Phœnicians, one of the early sea-going tribes living on the shores of the Mediterranean Sea. It is supposed that these sailors, building a fire on the seashore to cook food, may have propped their pots up on pieces of limestone, which furnished the lime, just as the beach furnished the sand, and the fire, the ash and the heat. Probably they found in the ashes of their fire a hard, greenish lump of glass. They did not know what it was, of course, but carried it away because it was clear and bright and pretty in colour, like a jewel. Wiser men, hearing their story, may have learned in this way how to mix sand, lime and soda-ash together and by heating it form glass.