MECHANICS.- 



In fig. 118 the wipers are" represented 

 Fig. 118. 



as lifting a forge hammer, which falls 

 on the anvil by its own weight. 



Another contrivance is represented 

 in fig. 1 1 9, somewhat similar to that 

 represented in fig. 103, but instead 



Fig. 119. 



of the wipers acting on a rod mov- 

 ing in guides, they act on a lever 

 working on a centre. The end of the 

 lever is pressed against the wipers by a 

 spring. 



The sun and planet wheel, invented 

 by Watt for his earlier double-acting 

 steam-engines, is another example of 

 this. To the end of a vibrating beam, 

 a connecting rod, A B, is attached, on 



Fig. 120. 



the lower end of which is fixed a tooth- 

 ed wheel, incapable of turning on its 

 centre. This wheel works in the teeth 

 of another, C, which turns freely on the 



centre, so that, as the one wheel is car* 

 ried round the other by the connecting 

 rod, it gives to the other a continued 

 rotatory motion. The alternate cir- 

 cular motion of the end of the beam 

 is thus made to communicate a contU 

 nued rotatory motion to the wheel. 

 In Jig. 121 is represented a contri- 



Fig. 121. 



vance on nearly the same principle as 

 the lever of Lagaroust. M N is a 

 wheel having teeth, or spindles, pro- 

 jecting from it in the manner of a 

 crown-wheel : A B is . a lever working 

 on the centre C ; D and E are two rods 

 turning on pins in the lever, and the 

 opposite ends of which are so formed, 

 as to press against the spindles, and 

 turn the wheel round. When the end 

 B of the lever is pressed towards the 

 wheel, the rod D presses the spindle,, 

 and urges the wheel round its centre. 

 By the same motion, the rod E, and 

 the spindle on which it rests, are se- 

 parated, and the rod E falls upon the 

 next spindle of the wheel. The end B 

 being then moved from the wheel, the 

 rod E presses upon the spindle, and 

 urges the wheel round its centre ; while 

 the rod D, and the spindle on which it 

 rests, are separated, and the rod D 

 falls upon the next spindle. In this 

 way the alternate circular motion of the 

 lever A B produces a continued circular 

 motion in the wheel M N. 



The various kinds of escapements 

 which are used in clock-work, are in- 

 stances of the same effect. The pen- 

 dulum has a reciprocating circular mo- 

 tion, and the wheel in connection with 

 it, and which it regulates, has a conti- 

 nued circular motion. 



(114.) To convert a reciprocating cir~ 

 cular motion into another reciproca- 

 ting circular motion. 



The means of accomplishing this are 

 numerous and obvious. If the two vi- 

 brations be round the same axis, it is 

 evident it may be done by fixing upon 

 the axes two arms or levers, presented 

 from the centre in the directions in 



