244 
PRUNING AND THINNING. 
[Part IV. 
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 mecha¬ 
nical 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, 
