Page:Philosophical Transactions - Volume 054.pdf/49

 Three trundles, with different numbers of staves; are applied to the cogs of a horizontal wheel with an upright axle; and the rope, which draws up the goods, coils round the axle. The wheel has 96 cogs, the largest trundle 24 staves, the next largest 12, and the smallest has 6. So that the largest trundle makes 4 revolutions for one revolution of the wheel and it's axle, the next largest makes 8, and the smallest makes 16. A winch is occasionally put upon the axis of either of these trundles for turning it; the trundle being used that gives a power best suited to the weight: and the handle of the winch describes a circle, in every revolution, equal to twice the circumference of the axle of the wheel. So that the length of the winch doubles the power gained by the revolutions of each trundle.

As the advantage gained by any machine or engine whatever, is in direct proportion of the velocity of the power to the velocity of the weight; the powers of this crane are easily estimated; and are as follows.

If the largest trundle be turned by the winch, it will make four revolutions for one revolution of the great axle on which the rope coils in drawing up the weight: and as the length of the winch is double the semidiameter of the axle, the power gained will be as eight to one: that is, a man will be able to raise eight times as much weight by means of the engine, as he could do by his natural strength without it; allowance being made for friction.

If the weight be too great for this power to raise, the second trundle may he turned by the winch, which will turn the wheel and axle twice as slow as LIV.