TABLE of Revolutions, per Mile, of Driving Wheels, and con sumption of Steam, Water, and Fuel, for each sized Wheel; taking the Steam admitted to each Cylinder as exactly one cubic foot at a gross pressure of 114·7 lbs., or 100 lbs. on the spring balance.

Power is compounded of the weight or expansive force of a moving body multiplied into its velocity.

THE power of a body which weighs 40 lbs., and moves with the velocity of 50 feet in a second, is the same as that of another body which weighs 80 lbs., and moves with the velocity of 25 feet in a

second; for the products of the respective weights and velocities are the same.

40 × 50 2000; and 80 × 25 = 2000.

Power cannot be increased by mechanical means.

Power is applied to mechanical purposes by the lever, wheel and axle, pulley, inclined plane, wedge, and screw, which are the simple elements of all machines.

The whole theory of these elements consists simply in causing the weight which is to be raised, to pass through a greater or a less space than the power which raises it; for, as power is compounded of the weight or mass of a moving body multiplied into its velocity, a weight passing through a certain space may be made to raise, through a less space, a weight heavier than itself.

Power is gained at the expense of space, by the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw.

LEVER.

Case 1. When the fulcrum of the lever is between the power and the weight.

RULE.-Divide the weight to be raised by the power to be applied; the quotient will give the difference of leverage necessary to support the weight in equilibrio. Hence, a small addition either of

leverage or weight will cause the power to preponderate.

EXAMPLE 1.—A ball weighing 3 tons, is to be raised by 4 men, who can exert a force of 12 cwt.: required the proportionate length of lever?

In this example, the proportionate lengths of the lever to maintain the weight in equilibrio, are as 5 to 1. If, therefore, an additional pound be added to the power, the power side of the lever will preponderate, and the weight will be raised. But, although the ball is raised by a force of only onefifth of its weight, no power is gained, for the weight passes through only one-fifth of the space. The products, therefore, arising from the multiplication of the respective weights and velocities are the same.

EXAMPLE 2.-A weight of 1 ton is to be raised with a lever 8 feet in length, by a man who can exert, for a short time, a force of rather more than 4 cwt.: required at what part of the lever the fulcrum must be placed?

20 cwt.

4 cwt.

= 5; that is, the weight is to the power as 8

5 to 1; therefore, 5 x 1

the weight.

1 foot and a third from

EXAMPLE 3.—A weight of 40 lbs. is placed one

foot from the fulcrum of a lever; required the power to raise the same when the length of the lever on the other side of the fulcrum is five feet?

CASE 2.- When the fulcrum is at one extremity of the lever and the power at the other.

RULE. As the distance between the power and the fulcrum is to the distance between the weight and the fulcrum, so is the effect to the power.

EXAMPLE 1.-Required the power necessary to raise 120 lbs., when the weight is placed six feet from the power, and two feet from the fulcrum? As 82: 120: 30 lbs., Ans.

EXAMPLE 2.-A beam, 20 feet in length, and supported at both ends, bears a weight of two tons at the distance of eight feet from one end; required the weight on each support?

RULE. As the radius of the wheel is to the radius of the axle, so is the effect to the power.

EXAMPLE.-A weight of 50 lbs. is exerted on the periphery of a wheel whose radius is 10 feet; re