Page:Philosophical Transactions - Volume 054.pdf/51

, and gives the weight liberty to descend. But if the descent be too quick, he pulls the lever a little farther down, so as to make it rub against the round edge of a wheel, by which means he lets the weight go down as slowly as he pleases; and, by pulling a little harder, he can stop the weight, if needful, in any part of it's descent. If he accidentally quits his hold of the lever, the catch immediately falls, and stops the whole machine.

In the figure of this crane [. 1.] A is the great wheel, and B it's axle on which the rope C coils. This rope goes over a pulley D in the arm of the gib E, and is hooked to the weight F for drawing it up. G is the winch, H the largest trundle, I the next largest, and K is the axis of the smallest trundle, which is suppofed to be hid from view by the upright supporter L. M is a trundle, which is turned by the great wheel; and on the axis of this trundle is fixt the ratchet wheel N, into the teeth of which the catch O falls. P is the lever, from which goes a rope QQ over a pulley R, to the catch; the end of the rope being fixed into the lever and catch. S is an elastic bar of wood, of which, one end is ferewed to the floor; and from the other end (out of fight in the figure) goes a rope to the farther end of the lever, beyond the pin or axis on which it turns in the upright supporter T. The use of this bar is to keep up the lever from rubbing against the edge of the wheel U, and to let the catch keep in the teeth of the ratchet-wheel. But, when the end P of the lever is pulled down, it lifts the catch out of the ratchet wheel by means of the rope QQ, and gives the weight F liberty to descend: Rh