OF STEAM ENGINES. 



171 



a nd such motion is given to it either by 

 wheel work, or by a gut-band passing 

 round a rigger or pulley fixed upon the 

 fly-wheel shaft, or some other revolving 

 part of the engine, and also round the 

 pulley c; and the relative velocities of 

 the governor and the engine must be ad- 

 justed by such wheel-work, or the respec- 

 tive diameters of the two pulleys. To- 

 wards the upper part of the rod or spin- 

 dle a b, two bent levers d e f and g e h 

 are fixed, so that they can both turn or open on the com- 

 mon centre e, which is fixed to the spindle ; a heavy iron ball 

 1 1 is fixed to the end of each bent lever, and the upper ends d 

 and g of these levers are attached by connecting links k k, with 

 joints to the sliding piece m, which slides freely on the square 

 spindle. It follows therefore that while the two balls i i lie in 

 contact with the spindle a b, the slider m will be pushed to its 

 greatest possible height upon the rod, but whenever the balls i 

 are opened out, the slider in must be depressed. The weight of 

 the balls keeps them in contact with the spindle, so long as it re- 

 mains stationary or moves slowly, but whenever their revolving 

 motion increases, their centrifugal force will drive them to a 

 greater or less distance from the centre : / n is an iron lever turn- 

 ing on the. fixed pivot n, while its opposite end enters a groove 

 formed in the sliding piece m ; this is merely for multiplying or 

 increasing the motion produced in m, when necessary ; for by 

 prolonging the distance between n and /, the end / may be made 

 to move in any required degr To apply the governor to the 

 regulation of the velocity of the engine, it therefore only be- 

 comes necessary to connect the end / of the lever by means of 

 strong wires with the lever of the throttle valve, taking care 

 that that valve shall be quite open when the two balls of the go- 

 vernor are lying close to their spindle, for then the engine will 

 move at its full speed. By so doing, the balls will instantly 

 separate and raise the end / of the governor-lever, which by 

 drawing upon the lever or the throttle valve will partly close it 

 and diminish the speed. 



The parallel motion still remains to be described, which 

 became necessary when the double acting engine was introduced. 

 This ingenious combination of simple levers is intended to ensure 

 the parallelism of the piston rod, and its operation may be best un- 

 derstood by reference to the following figure : p q represents 



