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APPLICATION Ot’ THE MACHINES. (Chap. 10

ARTICLE 94.

OF AN ELEVATOR APPLIED TO ELEVATE GRAIN, &C.,WROUGHT BY A MAN.

In Plate VII., fig. 18, AB, are two ratchet wheels,with two deep grooves in each of them, for ropes to runin; they are fixed close together, on the same shaft withthe upper pulley of the elevator, so that they will turneasily on the shaft the backward way, whilst a click fallsinto the ratchet, and prevents them from turning for-wards. Fig. 19 is a side view of the wheel, ratchet, andclick. CD are two levers, like weavers’ treadles, andfrom lever C there is a light staff passes to the foreside ofthe groove wheel B, and is made fast by a rope half wayround the wheel; and from said lever C there is a ropepassing to the backside of the wheel A; and from lever Dthere is a light staff passing to the foreside of the groovewheel A, and a rope to the backside of the groove wheel B.

The man who is to work this machine stands on thetreadles, and holds by the staffs with his hands: and ashe treads on D it descends, and the staff pulls the wheelA forward, and the rope pulls the wheel B backward,and as he treads on C, the staff pulls forward the wheelB, and the rope pulls backward the wheel A: but theclick falls into the ratchet, so that the w r heels cannotmove forward without turning the elevator pulley, it isthus moved one way by both treadles; and in order to keepup a regular motion, a heavy flying wheel F, is added,which should be of cast iron, to prevent much obstruc-tion from the air.

To calculate what quantity a man can raise to anyheight, let us suppose his weight to be 150 lbs., w hich isthe power to be applied; and suppose he be able to walkabout 70 feet up stairs in a minute, by the strength ofboth his legs and arms, or, which is the same thing, tomove his w r eight on the treadles 70 steps in a minute;then suppose we allow, as by Art. 29—42, to lose l-3dof the power to gain velocity and overcome friction,(which will be a large allowance in this case, because in