52 



MECHANICS. 



the effects of friction rob it of a certain 

 part of this force. 



A fly-wheel is not the only regulator 

 of force, and, even in cases vvhei e it is 

 used, we are sometimes obliged to have 

 recourse also to other contrivances. In 

 manufactures it generally happens that 

 there is one certain and determinate 

 velocity with which the machinery 

 should" be moved, and which, if in- 

 creased or diminished, would render the 

 machine unfit to perform the work it is 

 designed to execute. The application of 

 a perfectly-uniform power, aided by a 

 fly, will not effect this. For suppose, 

 as very frequently happens, the resist- 

 ance is changed by some of the ma- 

 chines, which are worked, being thrown 

 out of gear or an increased number put 

 on, the moving power having the re- 

 sistance thus diminished or increased, 

 will impart a greater or a less velocity 

 to the machinery, and all the fly-wheel 

 can do in this case is to maintain the 

 velocity uniform after it has been so in- 

 creased or diminished. 



To maintain an uniform velocity with 

 a varying resistance, one of the most 

 beautiful contrivances ever used is the 

 governor, an instrument used in mill- 

 work, but the application of which is 

 most conspicuous in the steam-engine, 

 when that machine is applied to manu- 

 facturing purposes. The principle on 

 which the efficacy of this instrument 

 depends, is easily explained. 



Let AB be a Vertical axis Which is 



made to revolve by the bevelled wheel A, 



acted on by the other parts of the ma- 

 chinery, and so that it always revolves 

 wiih a velocity proportional to that of 

 the fly-wheel. Two heavy balls C C' are 

 attached to metal rods, which work on 

 a pivot at B, so that they are capable 

 of receding from the axis A B. As 

 thev recede from the axis, the joints 

 D D' recede from one another, and the 

 joint E is drawn down. This joint E is 

 connected with the end of a lever or a 

 system of levers, the action of which 

 we shall presently explain. 



Now, by the revolution of the spindle 

 or axis A B, the balls C C' acquire an 

 obvious tendency to fly off from the 

 axis, and this tendency is resisted by 

 their weight, so that, when the instru- 

 ment is revolving with a certain velo- 

 city, the balls will remain suspended. 

 The property, from which this appa- 

 ratus derives its whole efficacy, is, that 

 at whatever distance or in whatever po- 

 sition the balls remain suspended, and 

 neither move to or from the axis, the 

 spindle A B must be revolving with the 

 same velocity. A greater velocity would 

 cause the balls to fly farther off, and a 

 lesser velocity would cause them to fall 

 towards the axis*. 



If the action of the levers with which 

 the joint E is connected, be directed 

 upon the first mover, in such a manner, 

 that its energy is diminished when E is 

 depressed, and increased when E is 

 elevated, it is plain that the uniformity 

 of velocity which is sought may be 

 obtained. Let us suppose that the 

 levers on which E woiks communicate 

 with a valve which admits steam to the 

 piston of a steam-engine to which this 

 governor is applied ; and suppose that, 

 when E is raised, and the balls C C' 

 rest in their seats, the valve is fully 

 open, so as to allow the steam to flow in 

 a full stream to the piston ; but that 

 according as E is depressed the levers 

 gradually close the valve, so as to admit 

 the steam in a constantly diminished 

 quantity. Now, suppose that the engine 

 has been working twenty printing 

 presses, and that the action of ten of 

 them is suddenly suspended. The 

 engine thus loses half its load, and 

 would, if the same power of steam con- 

 tinued to be admitted, move with about 

 twice its former velocity. But the mo- 

 ment an increased velocity is peiceived 



* 'i'his is strictly true only when the range of the 

 I**"* i small compared with the length o! (he rods 



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