Page:Philosophical Transactions - Volume 054.pdf/50

 the largest trundle did; because it makes twice as many revolutions for one revolution of the wheel and it's axle: and then the power gained will be as sixteen to one, because the velocity of the power will be sixteen times as great as the velocity of the weight.

If the weight be too great for this power to raise (which we will suppose to be exerted by one man) the winch may be put upon the axis of the third (or smallest) trundle, and then, in turning the winch, the power gained will be as thirty-two to one.

But if the weight should be too great, even for this power to raise, the power may be doubled by drawing up the weight by a double rope, going under a pulley in the moveable block which is hooked to the weight, below the arm of the gib; for then, the power will be as sixty-four to one. If the block has two pullies, and the rope be twice doubled below them, the power will be as 128 to one: and so on, by adding more pullies, according to any required proportion.

Whilst the weight is drawing up, the racch-teeth of a wheel slip round below a catch or click that falls successively into them; and so hinders the crane from turning backward, and detains the weight in any part of it's ascent, if the worker should happen accidentally to quit his hold of the winch; or choose to rest himself before the weight is quite drawn up. The catch, in this crane, is constructed much in the same way as in the great crane at Bristol, invented by the late Mr. Padmore, of that city.

In order to let down a weight, the man who works the crane pulls down one end of a lever of the second kind, which lifts the catch out of the