admission-, gas-, and exhaust-valves are all of the poppet type, and are operated through a cam-shaft and lever. Fig. 67 shows a section through one of the engine cylinders and its valve equipment, each cylinder being similarly arranged. A is the camshaft, B the admission-valve, and C the lever connected to the valve-stem. The valve action is as follows: If the machine is running at its rated speed, the admission-valve is lifted every fourth stroke, and as it rises its stem engages with a pawl on the stem of the gas-supply valve D, and lifts it, thus allowing gas to pass to the mixing-chamber, from which it enters the working cylinder through the opening of the admission-valve. If the engine tends to speed up, the fly-ball governor E shifts the pawl, and the gas-valve is not lifted; thus only air is supplied to the working cylinder, and an explosion is missed, this action continuing until normal speed is again reached. The method of ignition employed may be either the hot tube or the electric spark as desired. The exhaust is at F, the air-supply at H, and the gas-supply through G.

The Körting Gas-Engine is of the two-cycle type and secures the proportioning of air and gas by drawing these constituents into two separate cylinders whose volumes have the desired ratio. The pistons of this pair of cylinders are on the same rod and act to displace definite quantities of air and gas into the working cylinder. Hence the latter is not required to draw in the charge and is able to produce an impulse at each revolution, the other stroke being devoted to compression. Two such working cylinders are thus equivalent to the ordinary double-acting steamcylinder. Governing is effected by varying the time during which the working cylinder is open to the supply cylinders, thereby changing the amount but not the composition of the charge. In the Lackawanna Steel Company's Plant at Buffalo, N. Y., there are eight Körting gas-engines of 1000 H.P. each, and sixteen more of 2000 H.P. each are being installed. Five of these are directly connected to 500 K. W., three-phase, 25cycle, 440-volt, General Electric alternators, and the other three to 500-K.W., 250-volt, direct-current generators. The power cylinders of these engines are 244 inches in diameter with a stroke of 431 inches, developing 1000 H.P. at 100 r.p.m.

Mietz and Weiss Gas- and Kerosene-Engines.-This engine,

being of the two-cycle type, has its crank-chamber enclosed and the air-supply is moderately compressed in this space during the working stroke. An eccentric on the main shaft operates a small plunger by means of which the oil is injected into the cylinder. This oil is delivered upon a conical vaporizer preheated by a lamp in starting, but kept hot by the combustion after the engine is running. The air-charge is received from the crank-chamber through a port opened at the end of the impulse-stroke, after the exhaust-port has been opened, through which latter the spent gases escape. A deflector directs the incoming charge toward the head of the cylinder and away from the exhaust-ports. A valve limits the amount of oil injected, and the speed is automatically governed by varying the length of the stroke of the oilpump. This engine may be converted into a gas-engine by omitting the oil system, and providing a small auxiliary cylinder in which the gas is compressed to the same extent as the air, so that both are forced into the working cylinder and the spent gases expelled.

The following are the most important books relating to the gas-engine.

Gas-Engine Design, Dr. C. F. LUCKE.

The Gas-Engine, F. R. HUTTON.

The Gas- and Oil-Engine, Dugal Clerk.

Gas- and Petroleum-Engines, B. DUNCAN.
Gas-Engines, F. B. GOVER.

Die Verbrennung-Motoren, GULdner,
Les Moteurs de Gas, A. WITZ.

Noveaux Moteurs de Gas, S. RICHARD.

CHAPTER XIV.

WATER-WHEELS AND WINDMILLS.

WATER-WHEELS of various forms are, next to the steamengine, the most important prime movers for driving dynamos. The advantage of water-power is its cheapness; but it has the disadvantages of being rather difficult to regulate perfectly and maintain a constant speed with a variable load, and it is usually very unreliable, being scanty, or failing entirely, during the summer, and being liable to great trouble from ice and floods during the winter and spring. The enormous water-power at Niagara, which is practically constant throughout the year, is absolutely without a parallel; and in practically all other places considerable trouble is caused by excess or deficiency of supply at different seasons. For these reasons the cheapness of water-power is sometimes more apparent than real, and from the inevitable laws of demand and supply its cost becomes nearly equal to that of steam-power when everything is considered. For example, it is often necessary to have an auxiliary steam-plant in case of failure of water-supply or break-down of the plant; hence the interest, depreciation, etc., upon this steam-plant should be included in the total cost of the water-power. When, however, a reliable waterpower can be obtained, it usually enables electric current to be generated more cheaply than by steam-power; and there are many places in this country and abroad where this is very successfully accomplished. In fact, the practice seems to be almost universal to utilize, wherever available, a water-power for generating electricity for lighting or power purposes, even if the current has to be transmitted many miles.

Types of water-wheel formerly used were undershot, overshot, and breast wheels, but turbines and tangential or jet wheels. are the forms now generally adopted because of their greater efficiency and compactness.

Turbines are very extensively used for driving electric gen

erators, and possess the advantages of high efficiency,-being 80 to 85 per cent,-economy in space occupied, and close agreement in speed with that of the generator, so that the two can be directly coupled or easily connected by belting or gearing. They may be arranged to revolve either upon a vertical or horizontal axis; and there are also three types, depending upon the direction in which the water flows through the wheel. These are parallel-flow turbines, in which the motion of the water is approximately parallel to the axis of rotation; outward-flow turbines, in which the water is supplied at the center, and is discharged in currents radiating from it; and inward-flow turbines, in which the water enters at the periphery, and is discharged from the center. Turbines differ from other forms of water-wheel in the fact that all the buckets or blades are acted upon by the water at the same time, instead of only a portion of them, the action being equal and continuous on all sides. This tends to reduce the strains and friction, particularly with outward- and inward-flow turbines in which the pressures are almost entirely balanced in all directions. In the case of parallel-flow wheels the upward thrust can be made to relieve the weight, or two turbines may be combined so that their thrusts counteract each other.

B

A

B

The reason for the high efficiency of the turbine is the fact that the water after passing through the wheel leaves it with a small velocity; or, in other words, almost all of its energy is taken out. In this respect it is similar to the steam-turbine (Chap. XII), but the action is much simpler because no expansion or thermal changes need be considered. Let BB in Fig. 68 represent a portion of the fixed guide-blades of a parallel-flow turbine into which the water enters from above, as indicated by the arrow A, and strikes against the buckets of the wheel CC, causing it to revolve in the direction EF. The water is deflected by the curved blades of CC, until it flows out of the wheel in the direction DE. If the forward velocity of the wheel is EF, and the backward velocity of the water relative to the wheel is DE, then it is deliv

Fig. 68. Principle of the Turbine.

ered with an absolute velocity DF, about one-fifth of its original velocity when entering the wheel; thus nearly all of the energy is taken from the water and utilized to drive the turbine. If the wheel were designed to make the angle DEF smaller, the velocity > DF would be still further diminished; but a certain velocity is practically required in order that the water may be delivered and All other forms of turbine operate on the same principle; in the outward-flow wheel, for example, the water is brought to the center with a full velocity, and, after flowing outward in all directions, is delivered at the periphery with a velocity sufficient only to carry it out of the way of the water that follows it.

flow away.

The energy in a moving mass is proportional to the square of its velocity, beingm2: therefore, if the water issues from the wheel with only of its initial velocity, it retains only of the initial energy; or, in other words, 96 per cent of the kinetic energy has been taken from it. There are, however, other losses in a water-wheel to be considered. These may all be put in the following form:

In this expression Wis the weight in pounds of water flowing per minute; H is the total head or fall in feet: hence the first member is the total available H.P. P is the actual brake H. P. developed by the wheel; p is the H.P. lost in friction of bearings; h is the head lost in resistance to the flow of water through the wheel and passages leading to or from it; h, is the head lost by the fact that the total fall cannot be utilized, since the wheel is usually placed a certain distance above the lower water-level, but a large portion of this energy is often saved by the use of a draught-tube; v is the absolute velocity in feet per second at which the water issues from the wheel (represented by DF in Fig. 68); and g is the acceleration of gravity, equal to 32.2: hence the last term gives the H.P. remaining in the water due to the velocity with which it leaves the wheel.

Tangential Water-Wheels are provided with buckets projecting outward on the periphery, against which a jet of water issuing from a nozzle impinges tangentially (Fig. 72). For this reason