414 SUPPLEMENT. 



trundle, and turned round ; the power will be as 32 to 

 one. 



But, if the weight should be too great, even for this 

 power to raise, the power may be doubled by drawing 

 up the weight by one of the parts of a double rope, 

 going under a pulley in the moveable block, which is 

 hooked to the weight below the arm of the gib; and 

 then the power will be as 64 to one. That is, a man 

 could then raise 64 times as much weight by the crane 

 as he could raise by his natural strength without it ; be- 

 cause for every inch that the weight rises, the working 

 power will move through 64 inches. 



By hanging a block with two pullies to the arm of 

 the gib, and having two pullies in the moveable block 

 that rises with the weight, the rope being doubled over 

 and under these pullies, the power of the crane will be 

 as 128 to one. And so, by increasing the number of 

 pullies, the power may be increased as much as you 

 please : always remembering, that the larger the pullies 

 are, the less is their friction. 



Whilst the weight is drawing up, the ratch-teeth of a 

 wheel slip round below a catch or click that falls suc- 

 cessively into them, and so hinders the crane from turn- 

 ing backward, and detains the weight in any part of its 

 ascent, if the man who works at the winch should acci- 

 dentally happen to quit his hold, or choose to rest him- 

 self before the weight be quite drawn up. 



In order to let down the weight, a man pulls down 

 one end of a lever of the second kind, which lifts the 

 catch of the ratchet-wheel, and gives the weight liberty 

 to descend. But, if the descent be too quick, he pulls 

 the lever a little farther down, so as to make it rub 

 against the outer edge of a round wheel ; by which 

 means he lets down the weight as slowly as he pleases : 

 and, by pulling a little harder, he may stop the weight, 

 if needful, in any part of its descent. If he accidentally 



