THE LEVER AND WHEELWORK. 



261 



der, and by this means the relative velocity of wheels and pinions may be de- 

 termined according to any proposed rate. 



Wheel work, like all other machinery, is used to transmit and modify force 



in every department of the arts and manufactures ; but it is also used in cases 

 where motion alone, and not force, is the object to be attained. The most re- 

 markable example of this occurs in watch and clock work, where the object 

 is merely to produce uniform motions of rotation, having certain proportions, 

 and without any regard to the elevation of weights, or the overcoming of resist- 

 ances. 



A crane is an example of combination of wheelwork used for the purpose of 

 raising or lowering great weights. Fig. 28 represents a machine of this kind. 



Fig. 28. 



A B is a strong vertical beam, resting on a pivot, and secured in its position 

 by beams in the floor. It is capable, however, of turning on its axis, being 

 confined between rollers attached to the beams and fixed in the floor. C D is 

 a projecting arm, called a gib, formed of beams which are mortised into A B. 

 The wheelwork is mounted in two castiron crosses, bolted on each side of the 

 beams, one of which appears at E F G H. The winch at which the power is 

 applied is at I. This carries a pinion immediately behind H. This pinion 

 works in a wheel, K, which carries another pinion upon its axle. This last 

 pinion works in a larger wheel, L, which carries upon its axis a barrel, M, on 



