REGULATION OF MOTION BY FLY WHEELS. 63 



the motion of the machine slackens, it helps it 

 forward : if it tends to move too fast, it will keep 

 it back. 



Every regulating-wheel should be fixed upon 

 that axis where the motion is swiftest, and should 

 be heavy when the motion is designed to be slow, 

 and light where it is designed to be swift. In all 

 cases, the centre of motion should coincide with 

 the centre of gravity of the wheel. The axis may 

 be either perpendicular, or parallel to the horizon. 



A small force is sufficient to put a heavy wheel 

 in motion, which, if long continued, will accumu- 

 late in such a manner, as to produce effects in 

 raising weights and overcoming resistances, that 

 could not by any means be accomplished by the 

 application of the original moving force. 



On this subject, Mr. Atwood has demonstrated, 

 that a force of 20 pounds applied for 37 seconds to 

 the circumference of a cylinder of a 10 feet radius, 

 and weighing 4713 pounds, would, at the distance 

 of one foot from the centre, give an impulse to a 

 musket ball equivalent to what it receives from a 

 full charge of gunpowder. The same effect would 

 be produced in six minutes and ten seconds by a 

 man turning the cylinder with a winch one foot 

 long, in which he constantly exerted a force of 20 

 pounds. In this case, however, there is no abso- 

 lute increase of power ; for the cylinder has no 

 principle of motion in itself, and cannot have more 

 than it receives. 



This accumulation of motion, however, in heavy 

 wheels, is of great service in the construction of 

 machines for various purposes, rendering them 

 much more powerful, and easy to be worked by 

 animals, as well as more regular and steady, when 

 set in motion by water, or any inanimate power. 



