PI. IV. 



PEUNING AND THINJ^^ING. 



213 



that without two pulleys, that is, with the fixed pulley 

 only, and without the movable pulley also, no me- 

 chanical advantage is gained. But in the pruner's 

 pulley, even the single fixed pulley is dispensed with ; 

 yet, without any apparent mechanical advantage, half 

 is made equal to the whole. This paradox disgusts the 

 well-instructed engineer, even still more than it does 

 the most brutally ignorant man of plain common sense. 

 Truth, however, has a trick of being paradoxical, and 

 this truth is as true as that you can blow hot and blow 

 cold ; and it was only the brutally ignorant satyr who 

 denied that simple but paradoxical truth. 



But in the pruner's pulley the man is, in fact, at 

 once the movable pulley, the weight to be lifted, and 

 the power that lifts ; and the friction of the movable 

 pulley is saved while its mechanical advantage is 

 gained. Luckily, this is not a matter of opinion, but 

 a matter of fact ; and, practically, it may be proved 

 by children or weak persons, who are unable to raise 

 their weight on a single rope. Theoretically, it is in 

 perfect accordance with what in mechanics is called 

 ' the law of virtual velocities : ' for, if you ascend fifty 

 feet by a single rope, your hands pass over fifty feet of 

 rope ; and, for every foot your hands ascend, your 

 body ascends a foot. But if you ascend fifty feet by a 

 double rope, your hands pass over 100 feet of rope ; 

 and, for every foot your hands ascend, your body only 

 ascends half a foot, and your hands descend again half 

 a foot. Again, if you haul a weight up to a bough by 



