MECHANICS. 



415 



quits hold of the lever, the catch immediately falls, and 

 stops both the weight and the whole machine. 



This crane is represented thus : where A is the great 



wheel, and B its axle on which the rope C winds. This 

 rope goes over a pulley D in the end of the arm of the 

 gib E, and draws up the weight F, as the winch G is 

 turned round. H is the largest trundle, / the next, and 

 K is the axis of the smallest trundle, which is supposed 

 to be hid from view by the upright supporter L. A 

 trundle M is turned by the great wheel, and on the 

 axis of this trundle is fixed the rachet-wheel N, into the 

 teeth of which the catch O falls. P is the lever, from 

 which goes a rope Q Q, over a pulley R to the catch ; 

 or.e end of the rope being fixed to the lever, and the 

 other end to the catch. S is an elastic bar of wood, 

 one end of which is screwed to the floor : and, from the 

 other end goes a rope (out of sight in the figure) to the 

 further end of the lever, beyond the pin or axis on 

 which it turns in the upright supporter T. The use of 

 this bar is to keep up the lever from rubbing against 

 the edge of the wheel U, and to let the catch keep in the 



