Revolving about Fixed Axes. 



265 



tive of this qnestion by minute mathematical investigations, which 

 will be avoided as much as possible on this occasion, I will show 

 by a reference to the familiar examples of the common sling and 

 fly-wheel, that in a revolving body centrifugal force, whatever 

 be its source, is much greater than the power necessary to give 

 rotation to that body, and that it cannot therefore be directly 

 caused by the moving power, — and then explain how it may be 

 proved by a simple experiment. 



It has been stated above that writers on dynamics have not 

 clearly defined the operation of the laws of curvilinear motion 

 on bodies revolving about fixed axes. One only of the many in- 

 stances m which erroneous views are given by popular writers in 

 noticing the subject of central forces, will be mentioned. In 

 the Library of Useful Knowledge [London edition] a writer, 

 after enumerating some of the wonderful effects produced by ac- 

 ciimulating force in the circiunfei^ence of a fly-wheel, remarks : 

 " the same principle explains the force with which a stone may 

 be projected from a sling. The thong is swung several times 

 round by the force of the arm until a considerable portion of 

 force is accumulated and then it (the stone) is projected with all 



Fi£. 2. 



the collected force.* By observing the facts we may discover 

 how all this accumulation of force is produced by the strength 

 of the arm. A stone, S, Fig. 2, weighing one pound, secured to the 

 end of a string rather less than two feet long, may be whirled in 

 a circle of four feet diameter at the rate of two entire revolutions in 



* Vol I, p. 51, Art. Mechanics. 



