After Hector and he had gone as far in Dr Dick's astronomy as they could
understand, they found they were getting themselves into what seemed
quite a jungle of planets, and suns, and comets, and constellations.
"It seems to me," said the shoemaker, "that to understand anything you
must understand everything."
So they laid the book aside for the present; and Hector, searching about
for another with which to fill up the remainder of the afternoon, came
upon one in which the mechanical powers were treated after a simple
fashion.
Of this book Willie had now read a good deal. I cannot say that he had
yet come to understand the mechanical power so thoroughly as to see
that the lever and the wheel-and-axle are the same in kind, or that the
screw, the inclined plane, and the wedge are the same power in different
shapes; but he did understand that while a single pulley gives you no
advantage except by enabling you to apply your strength in the most
effective manner, a second pulley takes half the weight off you. Hence,
with the difficulty in which he now found himself, came at once the
thought of a block with a pulley in it, which he had seen lying about
in the carpenter's shop. He remembered also that there was a great iron
staple or _eye_ in the vault just over the well; and if he could only
get hold of a second pulley, the thing was as good as done--the well as
good as cleared out to whatever depth he could reach below the water.
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