So far we have not shown any combination of gearing that will multiply power. In Figure 5, the driver A is twice the diameter of the driven wheel B, and the latter makes two revolutions for one of A, but the speed at the periphery of the two wheels is the same. A pull of one pound at the point _a_ produces a pressure of one pound at _b_, and this in turn produces a lift of one pound at _c_ because the levers in each wheel are perfectly balanced, that is, each lever has equal effort and weight arms. The way to obtain an increase of power and of peripheral speed is to fasten two wheels of unequal diameters together on the same center and apply the effort to one of the wheels (as in Figure 12) and the weight to the other wheel. This gives us what is technically known as a _wheel and axle_. The dotted lines show that we have here a lever of the first order which can be used to multiply power in the same way that a bar lever does. If one wheel is twice the diameter of the other then a pound of effort will lift two pounds of weight. [Illustration: FIG. 12.--WHEEL AND AXLE OR REVOLVING LEVER OF FIRST ORDER] [Illustration: FIG. 13.--REVOLVING LEVERS OF THE 2D AND 3D ORDER] Figure 13 shows how the effort and weight can be shifted about in such fashion as to give us a lever of the second and one of the third order. The power may be enormously increased and the speed of the final wheel greatly reduced by setting up a train of gears in which the effort is received by the larger one of each couple and is delivered by the smaller one. In Figure 14 the smaller wheels are half the diameter of the larger ones. A pound of pressure at A will amount to 2 at B, 4 at C, 8 at D, 16 at E, and 32 at F. On the other hand, point A will have to move through 32 inches to make the point F move an inch. [Illustration: RAISING WATER WITH A CHAIN OF POTS A primitive pump still used in Egypt] [Illustration: A HORSE-OPERATED CHAIN-PUMP USED IN GREECE] [Illustration: MULTIPLE SPINDLE DRILL IN MOTOR CAR FACTORY] [Illustration: FIG. 14.--A TRAIN OF SPUR GEARS] [Illustration: FIG. 15.--PULLEYS OF THE 1ST, 2D, AND 3D ORDERS] [Illustration: FIG. 16.--TYPICAL ARRANGEMENT OF BLOCK AND TACKLE]