IG 



MECHANICS. 



river bottcms, where other means would fail. When a 

 Bteam-engine is used for lifting the ram, the work is more 

 rapidly performed. 



An interesting example of the nse and efficiency of 

 momentum is furnished by the water-ram^ a machine for 

 raising water, described on a subsequent page. 



The fly-wheel^ a large and heavy wheel used to regulate 

 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 thrasliing-machine, it has 

 been found that a heavy cylinder, by acting as a fly-wheel, 

 renders the motion steadier, and less liable to become im- 

 peded 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 

 Avater, erected a horsc-i>ump ; but at every stroke of the 



pump the animal was sud- 

 denly thrown loosely for- 

 ward, and again jerked back- 

 ward, as the piston fell light- 

 ly and rose heavily. A ny- 

 Avheol attached to the ma- 

 chinery woidd have prevent- 

 ed this unpleasant jerking, 

 and have enabled the horse, 

 in consequence, to accom- 

 l)lish more work. In the pile-driving engine, where a great 

 weight is suddenly 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. 



Where there is a rapid succession of forces required in 

 practice, the fly-wheel is usually of great advantage. 

 Hence its use in all revolvuig straw-cutters, where the 



Straw-cutter ivith Jly-ichccl. 



