Page:Popular Science Monthly Volume 9.djvu/211

Rh arranged to cleave, rather than to cut, the wood. Now, a calculation of the pressure necessary to thrust forward a wedge, and the impact necessary to cause the same wedge to enter the same depth, would explain why (regarded as a wedge only) the handle proves an important adjunct to the arm of the workman. Any one may test this by using an ordinary-handled hatchet on a soft straight-grained wood, or he may take a small axe with a straight and not a curved edge; let it rest upon a lump of moderately soft clay. Add weights until it has sunk to any decided depth, then take the axe by the head, and by pressure force the edge to the same depth. Next, hold the axe by the handle, first at, say, one foot from the head, then at two feet, then perhaps at three feet, and give blows which seem of equal intensity, and mark the depth. Thus a practical testimony to the value of a handle will be borne by the respective depths.

A few words about the motion of the hands and the handle they grasp; and then a consideration of the curves given to the cutting-edges of axes, adzes, etc.; also to the wedge-like sections of the edges. These will be all that can now be considered.

The motions of the hands on the handle of an axe are similar to those of a workman on that of the sledge-hammer. The handle of a properly-handled axe is curved, that of a sledge-hammer is straight. For present consideration this curvature may be overlooked, although it plays an important part in the using of an axe with success and ease. If the almost unconscious motions of a workman skilled in the use of an axe be observed, it will be noticed that, while the hand farthest from the axe-head grasps the handle at the same or nearly the same part, the other hand, or the one nearest to the head, frequently moves. Let us follow these motions and consider the effect of them. The axe has just been brought down with a blow and entered between the fibres of the wood. In this position it may be regarded as wedged in the wood, held in fact by the pressure of the fibres against the sides of the axe. From this fixity it must be released, and this is usually done by action on or near the head. For this purpose the workman slides his hand along the handle, and, availing himself (if need be) of the oval form of the handle after it has passed through the eye of the metal, he releases the head. The instrument has now to be raised to an elevation; for this purpose his hand remains near to the head, so causing the length of the path of his hand and that of the axe-head to be nearly the same. The effect of this is to require but a minimum of power to be exerted by the muscles in raising the axe; whereas, if the hand had remained near the end of the handle most distant from the head, then the raising of the axe-head would have been done at what is called a mechanical disadvantage. Indeed, if a workman will notice the position of the hand (which does not slide along the handle) before and after the blow has been given, he will find that its travel has been very small indeed. Remembering that