OF CRANES. 



95 



double weight hooked to the block of the moveable LECT. 



HI. 



pulley. v^v-v 



When only small burthens are to be raised, this may 

 be quickly done by men pushing the axle G round by 

 the hanjdspokes y, y, y, y ; having first disengaged the 

 trundle B from the wheel C : and then, this wheel will 

 only act as a fly upon the wheel F ; and the catch R 

 will prevent its running back, if the men should in- 

 advertently leave off pushing before the burthen be un- 

 hooked from /3. 



Lastly. When very heavy burthens are to be raised, 

 which might endanger the breaking of the cogs in the 

 wheel F, their force against these cogs may be much 

 abated by men pushing round the handspokes y,y>y,y, 

 whilst the man at A turns the winch. 



I have only shewn the working parts of this crane, 

 without the whole of the beams which support them ; 

 knowing that these are easily supposed, and that if they 

 had been drawn, they would have hid a great deal of the 

 working parts from sight, and also confused the figure. 



Another very good crane is made in the following Another 

 manner. A A is a great 

 wheel turned by men 

 walking within it at If. 

 On the part C, of its 

 axle B C, the great rope 

 D is wound as the wheel 

 turns ; and this rope 

 draws up goods in the 

 same way as the rope 

 H H does in the above- 

 mentioned crane, the 

 gib-work here being 

 supposed to be of the 

 same sort. But these 

 cranes are very danger- 



