in Mechanics, is a bar of iron or wood, one part of which being supported by a fulcrum, all other parts turn upon that as their centre of motion. This instrument is of two kinds. First, the common sort, where the weight which we desire to raise resting at one end, our strength is applied at the other, and the fulcrum is between both. When we stir up the fire with a poker, we make use of this lever; the poker is the lever, it rests upon one of the bars of the grate as a fulcrum, the incumbent fire is the weight to be overcome, and the other end held in the hand is the strength or power. In this, as in all the others, we have only to increase the distance between the strength and fulcrum, in order to give him who uses the instrument greater power.

The lever of the second kind has the fulcrum at one end, the strength is applied at the other, and the weight to be raised rests between them. Thus in raising the water-plug in the streets, the workman puts his iron lever through the hole of the plug till he reaches the ground on the other side, and, making that his prop, lifts the plug with his strength at the other end of the lever. In this lever also, the greater the distance of the fulcrum from the strength, the greater is the workman's power.

These instruments, as we see, assist the strength; but sometimes a workman is obliged to act at a disadvantage in raising either a piece of timber or a ladder upon one end. We cannot, with grammatical propriety, call this a lever, since such a piece of timber in fact in no way contributes to raise the weight. In this case, the man who is the strength or power is in the middle, the part of the beam already raised is the weight, the part yet at the ground is the fulcrum on which the beam turns or rests. Hence the man's strength will be diminished in proportion to the weight it sustains. The weight will be greater the farther it is from the fulcrum, therefore the man will bear the greater weight the nearer he is to the prop.