190 THE POPULAR SCIENCE MONTHLY. 



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 orna- 

 mentation 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 nat- 

 urally 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, differ- 

 ent conditions of edge are requisite. If the blow be given in the direc- 

 tion 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 in- 

 duced 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 pre- 

 liminary 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 cir- 

 cumstances 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 unsuitcd 

 for work across the fibre. The axe is simply a wedge, and therefore 



