The Wedge. When the compression of a block of wood is completed by the means of driving in a wedge, it then splits, and it is on this principle that the action of the wedge is founded. In the annexed diagram the explanation of the law may be seen. The point of the engine has been inserted by the blow of a hammer into a block of wood, and the wood by compression, has been displaced, and the block is rending because it can suffer no more compression. All the various kinds of cutting and piercing tools, as axes, knives, scissors, nails, pins, awls, are modifications of the wedge. The angle, in these cases, is more or less acute, according to the purpose to which it is applied.