223. =The Lever.=--The Lever is the most simple of all the Mechanical Powers, and is therefore in universal use. Though the savage makes use of but few tools in comparison with the civilized man, he uses the lever almost constantly in some form or other. The wedge is the only one of the other Mechanical Powers that he uses to any great extent. Levers are of three kinds, which I will notice separately. [Illustration: Fig. 157.] [Illustration: Fig. 158.] 224. =Lever of the First Kind.=--In the lever of the first kind the fulcrum or prop is between the weight and the power. The common crow-bar or hand-spike is a familiar example, as seen in Fig. 157--the stone, S, or other heavy body to be moved being the weight, the stone or block of wood, F, on which the bar rests being the fulcrum, and the pressure of the hand, H, the power. The nearer the fulcrum is to the weight, or the farther is the power from the fulcrum, the greater is the force of the lever. This may be illustrated on Fig. 158. Here the short arm of the lever, as it is called, C W, is one eighth of the length of the long arm, A C. If the weight hanging at the end of the short arm be 72 pounds, a weight of 9 pounds, or the force of a hand amounting to this, will balance it at the end of the long arm. But if the power should be applied at only four times the distance from the fulcrum at which the weight is, then it would require a force of 18 pounds to balance the 72 pounds on the short arm. Similar variations can be made by altering the length of the short arm. The power and the weight will balance each other if the weight multiplied by the length of the short arm, and the power multiplied by the length of the long arm, give equal products.