THE FLY-AVHEEL. 27 



great size are forced into the mud of swamps and riv- 

 er bottoms, where other means would fail. When a 

 steam-engine is used for lifting the ram, the work is 

 more rapidly performed. 



An interesting example of the use and efficiency of 

 momentum is furnished by the water-ram, a machine 

 for raising water, described on a subsequent page. 



THE FLY-WHEEL. 



Thefli/'iuheel, a large and heavy wheel used to reg- 

 ulate the motion of machinery, derives its value from 

 the power of inertia, or momentum, which prevents the 

 machine from stopping suddenly when it meets with 

 any unusual obstruction. In the common thrashing- 

 machine, it has been found that a heavy cyhnder, by 

 acting as a fly-wheel, renders the motion steadier, and 

 less liable to become impeded by large sheaves of grain. 

 An ignorance of this principle has sometimes proved a 

 serious inconvenience. A farmer, having occasion to 

 raise a large quantity of water, erected a horse-pump ; 

 but at every stroke of the pump the animal was sud- 

 denly tlurown loosely forward, and again jerked back- 

 ward, as the piston fell lightly and rose heavily. A 

 fly-wheel attached to the machinery would have pre- 

 vented this unpleasant jerking, and have enabled the 

 horse, in consequence, to accomplish more work. In 

 the pile-driving engine, where a great weight is sud- 

 denly thrown loose from a height, the horses would be 

 pitched forward when suddenly relieved of this load, 

 but for the regulation of a fly-wheel, the motion of 

 which is not quickly changed, neither from fast to slow 

 nor from slow to fast. 



