What other way have we for raising weights? We have the _wheel and axle_, as is shown in Fig. 53. [Illustration: Fig. 53.] What is the wheel and axle? The wheel and axle is only another form of the lever. Where is the power applied? The power is applied to the rope which passes around the wheel. Where is the weight? The weight is the bucket attached to the rope which passes around the axle. Where is the fulcrum? The fulcrum is the frame on which the ends of the axle rest. Is the power applied to the wheel equal to the weight to be raised? No; the power is always less than the weight to be raised. Upon what do the power and the weight depend? They depend upon the size of the wheel and the axle. When the diameter of the wheel is ten times the diameter of the axle, how much will one pound raise? One pound applied to the wheel, will then raise ten pounds on the axle. What is a windlass? A _windlass_ is another form of the wheel and axle, as is shown in Fig. 54. [Illustration: Fig. 54.] What is used in a windlass in place of the wheel? A crank or handle is used in place of the wheel. Does the crank take the place of the wheel? Yes; when the crank is turned, it forms a circle the same as the outside of the wheel. To what use is the windlass often applied? The windlass is often used to draw water from wells. Pulley. What is a pulley? A _pulley_ is a wheel with a groove or hollow cut in its edge. What is the groove for? The groove is cut so that a rope may move over the wheel without slipping off. [Illustration: Fig. 55.] In Fig. 55, where is the power applied? The power is applied to one end of the rope by the hand. Where is the weight? The weight is attached to the other end of the rope. When the power and the weight are equal, what do they do? They balance each other, and neither of them will move. When the power is greater than the weight, what takes place? The weight is then lifted up. Of what use is the single pulley? The single pulley is used for hoisting flags to the top of high poles, for raising sails to the topmasts of vessels, and for raising weights to the upper stories of mills and factories. How many pulleys are needed, when a horse is to raise the weight? When a horse is to raise the weight, two pulleys are needed, as may be seen in Fig. 56. [Illustration: Fig. 56.] To what use do farmers apply the pulley? They arrange the pulleys so as to lift the hay into their barns, by means of a horse; thus saving themselves much hard labor. Inclined Plane. When one end of a plank is raised up, while the other end remains on the floor, is its surface level? No; its surface is not level. What may the surface of the plank be called? It may be called an inclined surface, or an _inclined plane_. What is an inclined plane? An inclined plane is a surface that inclines upwards or downwards.