Page:Popular Science Monthly Volume 9.djvu/210

190 seen in the increased depth now given to the handle, where it enters the eye. It will be noticed that Fig. 5 is socketed as a carpenter's heavy mortising-chisel. The commendable pride of these prehistoric workmen in the beauty of their tools may be inferred from the ornamentation of these bronze axe-blades.

When we pass from the tool and its contrived handle to the mode of using, and the purpose for which it has been constructed, we find, as a rule, a cutting-edge formed by two inclined surfaces meeting at an angle, the bisecting line of which passes through the middle of the metal. It is very apparent that the more acute this angle is, the greater, under the same impact, will be the penetrative power of the axe into the material against which it is driven. This supposition very soon needs to be qualified, for suppose the material offers a great resistance to the entrance of this edge, then the effect of the blow, upon the principle that action and reaction are equal, will react upon the edge, and the weakest, either edge of axe or object struck, must yield. Here, then, primitive experience would be obliged to qualify the simple tool in which the edge was keen and acute, and would naturally sacrifice the keenness and acuteness to strength.

When early uses of the axe are considered, it will be noticed that, even in fashioning with an axe or adze the same piece of wood, different conditions of edge are requisite. If the blow be given in the direction of the fibre, resistance to entrance of the edge is much less than in the blow across that fibre. So great, indeed, may this difference become, that while the axe in Class 1 seems in all respects a suitable tool, yet as the attention of the workman passes to directions inclined to the fibre at an angle of more than forty-five degrees, he will be induced to lay aside the tools in Class 1, and try those in Class 2; for he will have found that while in the one direction of the wood the edge of his axe continues sound and efficient, yet a few blows on the same timber at right angles to this direction have seriously damaged the perfection of the edge, whatever may be the angle at which the faces meet which constitute the edge.

These remarks apply only to tools used in dividing materials, and not to tools used in preparation of surfaces of materials. This preliminary consideration prepares us for the different circumstances under which these two classes of tools may be respectively used. And as the contrast of the effect of the same tool under different circumstances in the same substance is considerable, great also is likely to be the contrast between the edges of the tools and the manner of using them, e. g., the axe, which is the proper tool in the direction of the fibre, is operated upon by impact, while a saw, which is the proper tool across the fibre, is operated upon by tension or thrust, but never by impact.

The mode in which the axe is used will explain why it is unsuited for work across the fibre. The axe is simply a wedge, and therefore