MECHANICS 418 



it might bo built in a room eight feet in width : the gib 

 being on the outside of the room. 



Three trundles, with different numbers of staves, are 

 applied to the cogs of a horizontal wheel- with an up- 

 right axle ; and the rope, that draws up the weight, 

 coils round the axle. The wheel has 96 cogs, the 

 largest trundle 24 staves, the next largest has 12, and 

 the smallest has 6. So that the largest trundle makes 

 4 revolutions for one revolution of the wheel ; the next 

 makes 8, and the smallest makes 16. A. winch is occa- 

 sionally put upon the axis of either of these trundles, for 

 turning it ; the trundle being then used that gives a power 

 best suited to the weight : and the handle of the winch 

 describes a circle in every revolution equal to twice the 

 circumference of the axle of the wheel. So that the 

 length of the winch doubles the power gained by each 

 trundle. 



As the power gained by any machine, or engine 

 whatever, is in direct proportion as the velocity of the 

 power is to the velocity of the weight ; the powers of 

 this crane are easily estimated, and they are as follows. 



If the winch be put upon the axle of the largest 

 trundle, and turned four times round, the wheel and 

 axle will be turned once round : and the circle described 

 by the power that turns the winch, being, in each re- 

 volution, double the circumference of the axle, when the 

 thickness of the rope is added thereto ; the power goes 

 through eight times as much space as the weight rises 

 through : and therefore (making some allowance for 

 friction) a man would raise eight times as much weight 

 by the crane as he would by his natural strength with- 

 out it : the power, in this case, being as eight to one. 



If the winch be put upon the axis of the next trundle, 

 the power will be as sixteen to one, because it moves 16 

 times as fast as the weight moves. 



If the winch be put upon the axis of the smallest 



