STEAM AND GASOLINE ENGINES 



185 



in the first cylinder. These latter engines are called double- 

 expansion or, if three cylinders receive the steam one after 

 another, triple-expansion engines. 



The free end of the piston rod is attached by a movable 

 joint to the crank shaft a shaft with a right-angled bend to it 

 like the crank for an automobile or that on a grindstone or coffee 

 mill so that the back-and-forth motion of the piston rod is trans- 

 formed to a rotary motion of the shaft and its attached flywheel. 



The governor on many 

 engines now is very like 

 the one devised by Watt. 

 A solid vertical rod has 

 firmly fixed near its lower 

 end a wheel which by 

 teeth or belt is geared to 

 a rotating shaft of the 

 engine and the rod thus 

 rotates rapidly about 

 its longitudinal axis 

 (Fig. 73) . Two arms are 

 jointed by one end to 

 opposite sides of the 

 upper end of this rod. 

 Near the lower free end 

 of each arm there is fixed a heavy metal ball. A rod is attached near 

 the end of each free arm and runs thence to a collar that encircles 

 the rod several inches below the level of the balls. The rods 

 attach to this collar by a movable joint. This collar fits into 

 another one just below it so that the lower one must move up and 

 down with it but need not revolve with it. As the vertical rod 

 rotates, the balls attached to the arms whirl about and stand 

 away from the rod on account of centrifugal force. The faster the 

 rotation, the farther away they move. As they move out the 

 rods attached just above them pull the collar up on the vertical 

 rod. To the second collar a rod attaches that runs to the valve 



FIG. 73. Diagram of the governor of a steam 

 engine. 



