The Governor.—The automatic device used to control either the throt tle or the point of cut-off is called a "governor." Its most common form, the centrifugal fly-ball type (pi. 82, 5), was invented by Watt.
Farco4 Cenlriftegal Governor.—In the Farcot centrifugal governor, shown in Figure 15 (pl. 83), there are connected with the extended shaft of a conical pendulum (driven by a horizontal shaft seen below) two fric tion plates. Between these there is a pair of conical wheels which engage with the upper or the lower of these friction plates according to the in crease or decrease in the engine speed, moving the conical wheels to the left or to the right as the case may be. The conical wheel of the upper horizontal shaft gearing into these conical wheels is, together with the shaft, moved to the left or to the right, and moves by a screw in one or the other direction the spindle of the expansion-valve. When the con ical pendulum is in its normal position by reason of the engine speed and its own being normal, neither of the friction plates is disengaged.
Allen Governor.—Figures 12 and 13 show the Allen governor, in which there is a paddle-wheel in a corrugated cylinder filled with oil (fig-. 13). Increase of engine speed tends to turn the cylinder faster about the wheel, and by means of a segment gear this motion is made to move the cut-off to an earlier point.
Buckeye are very many successful engines in which there is a centrifugal governor upon the main shaft; a variation in the rotation speed, due to change of load or of initial pressure, causes the weights to approach or recede from the centre, and the levers to which they are attached to vary the angle which the eccentric makes with the crank, or its amount of eccentricity, thus varying the point of cut-off, and in many of these engines other functions, such as the times of steam admis sion and exhaust opening, and the point at which the exhaust is closed. Of this "Harwell " type the "Buckeye" is the best known (pl.s3, fig. 16).
Ball's are regulators by which the amount of throt tling or the earliness of cut-off is controlled in proportion to the load and not to the speed, as in the Ball engine, the governor of which is shown in Figure 14.
Rotapy Engines, while having the advantage of being able to run with great speed and with little jar, cannot very well work steam expansively. The difficulty of keeping them tight is due to the fact that friction is pro portionate to the speed of the wearing surfaces, and the exterior of a revolv ing circle must of necessity travel faster than portions nearer the centre. Hence it is almost impossible to keep the ends of such rotating cylindrical pistons or "followers" packed. The extreme simplicity of such engines, and the convenience with which they may be used for " direct-driving'' high-speed machinery, such as circular saws, would make them very pop nlar if they were not so wasteful of steam and so difficult to pack. Fig ures 5 and 6 (pi. 85) show Kenyon's rotary engine, in which the steam is admitted and permitted to exhaust by a slide-valve. As shown in Figure 6, it is exhausting from the left-hand side and taking steam at the right; the direction of motion being contrary to that of the hands of a watch. In Figure i is shown Runkel's rotary engine, in which a rotat ing piston or follower is made to turn a crank, thus combining all the disadvantages of both the reciprocating and the rotary type. Figure 2 (pM. 84) shows Turner's; Figure 3, Cox's; Figure 7 (y5/. 85), Hall's; and Figure 2, Borries' rotary engines.
Marine Engines are for the most part vertical, and are generally what are known as " inverted "—that is, the cross-head is below the cylinder unless there is a beam. Marine service necessitates high economy of steam, hence compounding and condensing are carried to the utmost pos sible grade of perfection. The modern ocean steamer requires from 5000 to zo,000 indicated horse-power to propel her 500o to 15,000 tons' burden at speeds which, while increasing almost with each successive high-grade vessel, now reach the average rate of 20 knots or statute miles per hour between Queenstown and Sandy Hook.