Page:Philosophical Transactions - Volume 054.pdf/46



common crane consists only of a large wheel and axle; and the rope, by which goods are drawn up from ships, winds or coils round the axle, as it is turned by men walking in the wheel. But, as these engines have nothing to stop the weight from running down, if any of the men happen to trip or fall in the wheel, the weight descends, and turns the wheel rapidly backward, and tosses the men violently about within it; which has produced melancholy instances, not only of limbs broke, but even of lives lost, by this ill-judged construction of cranes. And besides, they have but one power for all forts of weights; so that, they generally spend as much time in raising a small weight as raising a great one.

These dangers and imperfections made me think of a method of remedying them. And for that purpose, I have contrived a crane with a proper stop to prevent the danger, and with different powers suited to different weights; so that there might be as little loss of time as possible: and also, that when heavy goods are let down into ships, the descent may be regular and deliberate.

This crane has four different powers: and, I believe, it might be built in a room eight feet in width; the gib being placed on the outside of the room. Rh