94 FERGUSON'S LECTURES. 



LECT. of the weight 0, which is just sufficient to keep its end 

 ^-v^, L up to the rope ; so that, as the great axle turns, and 

 the rope coils round it, the lever rises with the rope, and 

 prevents the coilings from going over one another. 



The power of this crane may be estimated thus : sup- 

 pose the trundle B to have 13 staves or rounds, and the 

 wheel C to have 78 spur cogs ; the trundle E to have 

 14 staves, and the wheel F 56 cogs. Then, by multiply- 

 ing the staves of the trundles, 13 and 14, into one an- 

 other, their product will be 182 ; and by multiplying the 

 cogs of the wheels, 78 and 56, into one another, their 

 product will be 4368, and dividing 4368 by 182, the 

 quotient will be 24 ; which shews that the winch A 

 makes 24 turns for one turn of the wheel F and its axle 

 G on which the great rope or chain H I H winds. So 

 that, if the length or radius of the winch A were only 

 equal to half the diameter of the great axle G, added to 

 half the thickness of the rope H, the power of the crane 

 would be as 24 to 1 : but the radius of the winch being 

 double the above length, it doubles the said power, and 

 so makes it as 48 to 1 : and in which case, a man may 

 raise 48 times as much weight by this engine as he could 

 do by his natural strength without it, making proper al- 

 lowance for the friction of the working parts. Two 

 men may work at once, by having another winch on the 

 opposite end of the axis of the trundle under B ; and so 

 make the power still double. 



If this power be thought greater than what may be 

 generally wanted, the wheels may be made with fewer 

 cogs in proportion to the staves in the trundles ; and so 

 the power may be of whatever degree is judged to be 

 requisite. But if the weight be so great as will require 

 yet more power to raise it (suppose a double quantity) 

 then the rope H may be put under a moveable pulley, as 

 8, and the end of it tied to a hook in the gib at a ; which 

 will give a double power to the machine, and so raise n 



