by it passing to the boiler. The central portion of the grate bars consists of shaking grates, while the side bars are stationary and inclined.

Fig. 126 is a sectional view and will serve to illustrate the construction of this furnace. The coal is fed through pockets on top on each side of the arch, the larger furnaces having two pockets on each side and the smaller sizes one. The doors in front are only

opened for the purpose of cleaning fires or when first starting fires. The air is supplied by way of the ash pit, passing up through the grate bars. A portion of the air supply is also drawn through the ventilators and passes to the upper part of the furnace.. The arch. extends under the front end of the boiler 6 or 8 in., and there is a bridge wall about 4 ft. back from the front against which the gases from the furnace impinge.

There are 42 sq. ft. of grate surface in the larger

sizes, and 22 sq. ft. in the smaller size. Good combustion is attained in this furnace, owing to the fact that the gases as they are distilled from the coal come immediately in contact with the highly heated surface of the arch directly over the fire.

THE STEAM TURBINE

The steam turbine-Lack of information concerning steam turbines-Points of difference between the turbine and the reciprocating engine-Kinetic energy in steam-Hero's steam turbine-Branca's steam turbine-Fundamental principles of the steam turbine-Types of steam turbines built in the United States-The Westinghouse-Parsons turbine-Theoretical velocity of steam exhausting into a vacuum-Relation of bucket speed to steam speed-Speed of the WestinghouseParsons turbine-Description of cylinder and blades-Relation of stationary to moving blades-Curvature of bladesAction of the steam within the turbine explained-Balancing pistons-Construction of bearings-A floating journal-Lubrication of bearings-Water seal packing-Speed regulation— Description and diagram of governor-Efficiency of steam turbines-Tests of Westinghouse-Parsons turbines.

Although the turbine principle of utilizing the energy in steam and converting it into useful work has been experimented upon for many years, it is only since the inauguration of the twentieth century that steam turbines have been brought to the front as efficient power producers.

There are to-day in this country four distinct types. of steam turbines, each one of which has its own characteristic features distinguishing it from the others, but in each the kinetic energy and velocity of the expanding steam constitute the source of power.

Notwithstanding the fact that much has been said and written during the past four years regarding the steam turbine, the machine is to-day a mystery to thousands of engineers, not because they do not desire

information upon the subject, but because of a lack of opportunities for obtaining that information. The author therefore considers that a space devoted to this subject would no doubt be of benefit to his readers.

The piston of the reciprocating engine is driven back

and forth by the static expansive force of the steam, while in the steam turbine not only the expansive force is made to do work, but a still more important element is utilized, viz., the kinetic energy or heat energy latent in the steam and which manifests itself in the rapid vibratory motion of the particles of steam

expanding from a high to a lower pressure, and this motion the steam turbine transforms into work.

One of the earliest descriptions of a device for converting the power of steam into work was recorded by Hero, a learned writer who flourished in the city of Alexandria in Egypt, in the second century before Christ. Hero describes a machine called an Æolipile or "Ball of Æolus," illustrated in Fig. 127. B is the boiler under which a fire was made. G is a hollow

FIGURE 128.

metallic globe that revolved on trunnions C and D, one of which terminated in a pivot at E, while the other was hollow and conveyed the steam generated in the boiler B to the interior of the globe or ball, from which it escaped through the hollow bent tubes H and I, and the reaction of the escaping steam caused the globe to revolve. This was the first steam turbine, and it worked on the reaction principle.

Many centuries later, in the year A.D. 1629, Branca, an Italian, described an engine which marks a change