Page:Popular Science Monthly Volume 9.djvu/213

 Rh or ought to be, sufficient to retain it, and the whole of the energy-resulting from muscular action and gravity should be utilized. The curvature, too, of the handle is in marked contrast with the straight line of the sledge-hammer handle. The object of this curvature is worthy of note. In my hand is an American forester's axe. The handle is very long and curved. If, laying the axe-handle across my finger where the head and handle balance, I place the blade of the axe horizontally, you may notice that the edge does not turn downward; in fact, the centre of gravity of the axe-head is in the horizontal straight-line prolongation of the handle through the place where my finger is. Now, in sledge-hammer work the face is to be brought down flat, i. e., as a rule, in an horizontal plane. Not so with the forester's axe: it has to be brought down at varying obliquities. If, now, the hewer's hand had to be counteracting the influence of gravity, there would be added to him very needless labor; hence the care of a skilled forester in the balance of the axe-head and the curvature of the handle.

We must now consider the form of the cutting-edge as seen in the side of the axe. It is often convex. The line across the face in Fig. 7 indicates the extent of the steel, and the corresponding line in Fig. 8 the bevel of the cleaving edge. It will be noticed that the cutting-edge in each case is curved. The object of this is to prevent not only the jar and damage which might be done by the too sudden stoppage of the rapid motion of the heavy head in separating a group of fibres, but also to facilitate that separation by attacking these fibres in succession. For, assuming that the axe falls square on its work

in the direction of the fibres, a convex edge will first separate two fibres, and in so doing will have released a portion of the bond which held adjoining fibres. An edge thus convex, progressing at each side of the convexity which first strikes the wood, facilitates the entrance of successive portions from the middle outward. If the edge had been straight and fallen parallel to itself upon the end of the wood, none of this preliminary preparation would have taken place; on the contrary, in all probability there would have been in some parts a