The power of these teeth or notches may be inferred from a well-known fact. If a razor, no matter how sharp, be pressed upon the human skin without any “draw,” it will indent the skin, but not cut it, while the slightest drawing movement will cause a deep wound. It is the knowledge of this fact that enables an expert swordsman to sever an apple placed on the palm of the bare hand, without even scratching the skin. I have witnessed this feat, and at once saw that it was due to the absence of any “draw” to the cut. The apple was laid on the palm of the hand, which was opened as widely as possible, so as to flatten it. The sword was then brought down on the apple with a sort of chopping movement, so that, although it indented the skin, it did not even inflict a scratch. By the use of the “drawing” movement, the same sword severed a gauze veil laid across it, the two halves floating in opposite directions. By the same cut, I have seen some astonishing feats performed with an Indian sword now in my collection, the objects of attack falling asunder as if by magic, without any apparent force being used. * * * * * HAVING now glanced at the principle of the Saw, we will proceed to some of its details. The simplest form of Saw in existence is that which is in use among the Australian natives, and consists of obsidian flakes set along one side of a stick. It looks a rude and inefficient affair enough, but it can cut better than might have been thought, as I can testify from experiments on such a saw in my collection. [Illustration: SAW OF COMMON SAW-FLY (MAGNIFIED). GROOVES CUT BY SAW IN BARK.] [Illustration: HAND-SAW. TENON SAW. PIONEER’S SAW-SWORD.] Many as are the varieties of the Saw, the principle is the same in all, and the chief distinction lies in the shape and arrangement of the teeth, according to the work which they have to do. Watch-spring Saws, for example, which have to cut metal, have their teeth so slight as to be hardly perceptible, and arranged nearly in a line with each other. The Fretwork Saws, which have to cut delicate patterns in wood, with the slightest possible waste of material, are of the same character. Then we have the long curved teeth of the Circular Saws, which tear their way savagely through great tree-trunks, and fill the air with clouds of sawdust. There are also the Tenon Saw, with its thin blade and broad back; the pioneer’s saw for cutting green wood, with its double array of teeth, so as to make a wide “kerf” in which it shall not be clogged; together with many others that we cannot enumerate here. * * * * * WE will now examine some Saws as found in Nature.