1692. The common character of tools is, that they are adapted for labour which requires more force than skill; they are generally large, and require the use of both hands and the muscular action of the whole frame, often aided by its gravity. Tools consist of two parts, the head, blade or acting part; and the handle or lever, by which the power is communicated, and the tool put in action. As almost all tools operate by effecting a mechanical separation between the parts of bodies, they generally act on the principle of the wedge and lever, and consequently the wedge-shape ought to enter, more or less, into the shape of the head or blade of most of them, and the lever or handle ought to be of some length. Where the handle is intended to be grasped and held firm, its form may be adapted for that end, as in the upper termination of the handle of the shovel or the spade; but where the human hand is to slide along the handle, then it should be perfectly cylindrical, as producing least friction, as in the hoe and the mattock. The materials of which tools are composed are almost exclusively iron and timber; and of the latter the ash is reckoned to combine most strength and toughness, the willow to be lightest, and fir or pine deal the straightest. The best quality of both materials should, if possible, be used, as scrap-iron and cast-steel, and root-cut young ash from rocky steeps. For light tools, such as the hoe and the rake, willow wood, or pine deal, may be used for the handles, but in scarcely any case can inferior iron or steel be admitted for the blades.