410 SUPPLEMENT. 



teeth of the ratchet-wheel : But a weight hung to the 

 farther end of the lever would do full as well as the 

 elastic bar and rope. 



When the lever is pulled down, it lifts the catch out 

 of the ratchet-wheel, by means of the rope Q Q, and 

 gives the weight F liberty to descend : but if the lever 

 P be pulled a little farther down than what is sufficient 

 to lift the catch out of the rachet-wheel N, it will rub 

 against the edge of the wheel U, and thereby hinder 

 the too quick descent of the weight ; and will quite stop 

 the weight if pulled hard. And if the man who pulls 

 the lever, should happen inadvertently to let it go ; the 

 elastic bar Avill suddenly pull it up, and the catch will 

 fall down and stop the machine. 



W W are two upright rollers above the axis or upper 

 gudgeon of the gib E : their use is to let the rope C 

 bend upon them, as the gib is turned to either side, in 

 order to bring the weight over the place where it is in- 

 tended to be let down. 



N. B. The rollers ought to be so placed, that if the 

 rope C be stretched close by their utmost sides, the half 

 thickness of the rope may be perpendicularly over the 

 center of the upper gudgeon of the gib. For then, and 

 in no other position of the rollers, the length of the rope 

 between the pulley in the gib and the axle of the great 

 wheel will be always the same, in all positions of the 

 gib : and the gib will remain in any position to which it 

 is turned. 



When either of the trundles is not turned by the 

 winch in working the crane, it may be drawn off from 

 the wheel, after the pin near the axis of the trundle is 

 drawn out, and the thick piece of wood is raised a little 

 behind the outward supporter of the axis of the trundle. 

 But this is not material ; for, as the trundle has no fric- 

 tion on its axis but what is occasioned by its weight, it 

 will be turned by the wheel without any sensible resist- 

 ance in working the crane. 



