In the Middle Stone Age we find the primitive craftsman equipped with a very complete assortment of stone tools. He had hammers, chisels, scrapers, drills, and polishing tools. He knew how to make useful household implements, such as spoons and ladles, out of bone. He polished his work and ornamented the implements with carvings of animals. Ivory pins and needles show that he had begun to make himself clothing from the skins of animals and that he sewed them together with thongs or tendons. In the Late Stone Age he had learned how to make vessels of fire-baked clay. His axes were ground to a sharp edge, and he bored holes in the ax head to receive the ax handle. The Swiss lake dwellers built houses of wood and fitted them with all sorts of wooden furniture carved with stone tools. Among the remains of these interesting settlements may be found balls of clay which, from the fact that one of them was discovered with a spool of flax still attached to it, were evidently used as spinning “whorls” used for spinning flax into thread. Clothing of skins was giving way to or being supplemented with clothing of woven fabric. DISCOVERY OF THE LEVER AND THE WEDGE Prior to the Stone Age the club was undoubtedly used, in time of peace--if there ever was a time of peace in those days--to batter down trees, to beat through entanglements and to dislodge great stones. Here the first idea of leverage was evidently employed. The club with a rock tied to it, particularly if the rock was shaped with a sharp edge, made a better implement for hewing trees. It is quite probable that soon after this stage of development had been reached, some one discovered the use of the wedge, particularly in splitting timber. Of course, no one realized in those early days why it was that he could pry up a greater weight with a lever than he could lift directly by hand, or why he could split open a log by driving wedges into it. The _art_ of mechanics was in existence long ages before _science_ of mechanics began to be studied. But it was not until men began to look into the why of things that rapid progress was made.