WATER POWER. Water power is de rived from the conversion of the energy of fall ing water into mechanical work. If a volume of water having a weight tv in pounds is situ ated at a height It in feet above a plane of reference, it possesses a potential energy re X It in foot pounds, all of which can be converted into kinetic energy by allowing the water to fall through the height h. If the water in fall ing passes through a suitable hydraulic motor, most of its potential energy can be converted into useful mechanical work, in which case the water will reach the bottom of the fall with little or no energy remaining, instead of having its full energy remaining in kinetic form, as it would do if it fell freely and unrestricted. In practice, water power is psually derived from running streams, and the amount of power is expressed in terms of the rate at which energy is supplied to or derived from the hydraulic motor. The ratio of the rate at which energy is derived from an hydraulic motor to that at which it is supplied to the motor is called the 'efficiency' of the motor. The amount of power may be expressed in terms of the rate at which energy is supplied, or the rate at which mechanical work can be performed by the motor. The former is called the 'theoretical power' of the water or stream supplying the motor.
One horse power, as defined by NA'att, repre sents energy sufficient to raise a weight of 33, 000 pounds one foot high per minute, or in other words. 33,000 foot-pounds per minute. or 550 foot-pounds per second. Fresh water weighs 62.42 pounds per cubic foot. hence the theoreti cal horse power of a constant stream of water. flowing in a volume of q cubic feet per second, and falling through a height of A feet, is equiva lent to 62.42 X q X It horse power.
550 This reduces to the simple rule— Theoretical horse power of water = 0.1135 X q X h, The output or derived power of an hydraulic motor, or of a water power, is the product of the theoretical power multiplied by the effi ciency expressed as a decimal, or if the eth ciency is E, then the mechanical or brake horse power is equal to 0.1135 xqXhXF..
Efficiency may be considered with reference to the hydraulic motor alone, or with reference to the entire power plant, including allowances for losses of power in electric generators and other equipment in the case of hydro-electric plants. If used in the latter sense it is termed
"over-all efficiency,' and the theoretical horse power, multiplied by the over-all efficiency, represents the net rate of power output by the plant or power development.
Water power ranks with mines and the soil as one of the greatest natural sources of wealth. Coal and oil supply at present the greater por tion of the fuel and energy used in the world, but this supply is exhaustible. The soil fosters organic growth, which is capable of suppxil energy resources chiefly in the forms of and of alcoholic fuels. These sources of energy, hire water power, are perpetual, but are at pres ent relatively much less important.
Machines or organisms through the operation of which useful mechanical work is derived from natural sources of energy are called *prime movers.' There are organic or living prime movers which derive useful mechanical work from- the latent energy contained in the food they eat. Men and horses are found to be relatively inefficient as prhne movers. The human body is capable of yielding back through muscular work only about one-fifth of the avail able energy supplied to it as food. Another class of prime movers consumes fuel and con verts its potential energy into kinetic energy by means of steam, gas and oil engines. Both the preceding classes may be considered as fuel en gines. They derive energy from highly organ ized compounds which have originated in life processes. These are broken down into simpler compounds by the processes of digestion or com bustion, and in accordance with a rule of nature, they Ore up a supply of stored energy as they are disintegrated. The supply of power from chemical reduction being dependent upon life processes, can be renewed by a perpetuation of life, but unfortunately fuel consumption at the present time greatly exceeds the rate of re newal, and we are mainly dependent on the great storehouse of latent energy given us as a legacy from past ages in the form of coal, oil and gas. The power consumption at the present day, if derived from wood alone, would exhaust our timber supply in a few years. In the early days of railroads, wood was used as fuel in locomo tives. Few of us realize the extent to which the forests were devastated to supply that need.