424 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



whole area of the pipe is free for the passage of the steam. This is 

 called the throttle valve. The other arm of the lever, moving the valve, 

 is connected with the end L of the lever ML in such a way that as the 

 collar M rises, lowering the point L, the valve is turned more across 

 the steam-pipe, thus reducing the area of the steam-passage and 

 lowering the speed of the engine. The flow of steam is therefore 

 diminished when the velocity of the engine passes the normal limit ; 

 it is introduced, on the contrary, in greater abundance when there is 

 a falling off. 



Two other systems of regulators are employed besides these, the 

 arrangement of which is very slightly different from that of the centri- 

 fugal regulator (known also by the names of Watt's governor). Both 

 are founded, like the first, on the action of the centrifugal force 

 applied to masses which turn on an axis set in motion by the 



