2 Tho weight which may be balanced by a given power r will evidently be greater as r'—r, or the difference between the radii of the cylinder, is less; and the difference may be made very small without much increasing the friction. The only disadvantage attending the machine, when compared with an ordinary winch or capstan, is that it requires; a much greater quantity of rope to raise or move the object through any given distance. It was first proposed in Europe by Mr. George Eckhardt, but machines of a like kind have, it is said, been long in use in the East, The winch is employed with the common jack, which is used to lift great weights, or to move them through small distances. The handle turtle a pinion with teeth, which act on others at the circumference of a small wheel; and on the axle of this is a pinion with tooth which work in those ofa rack-rod. The axles of the wheel and pinions being let into the sided of a case of wood or iron, the revolution of the wheel produces a rectilinear motion of the rack ; and one end of the case being fixed to the ground, or against an immoveable object, the extremity of the rack at the opposite end forces forward the body which is to be displaced. Sometimes, instead of a rack, the machine is furnished with a wheel whose axle is hollow, and cut in the form of a concave screw ; within this screw is one of the convex kind, which by the revolution of the wheel and its axle is made to move in the direction of the latter, and thus to press before it the object which is to be removed. This machine
has however considerable friction.
The force exerted by a man in turning a winch vertically varies according to the position of the lever with respect to the horizon. When the lever, or that part which is perpendicular to the axle, is per pendicular to the ground, and the handle is at the highest or lowest part of the circle described by the end of the lever, the man either pushes the handle directly from hint, or pulls it directly towards him ; and in each case he exerts a power which is estimated at 27 or 30 lbs.; but when the lever is in a horizontal posi tion, the man either throwa a great portion of his weight on the handle to press it down, or he exerts his muscular force in a direct manner to pull it upwards; and the force exerted in these positions is estimated at 140 or 160 lba. The force exerted must evidently have different values between these quantities in other posi tions of the winch ; and the practice is to cause two men to work at the same time to turn the machine, one being at each extremity of the axle of the cylinder. The levers of the two winches are placed at right angles to one another ; consequently when one man is pushing or pulling horizontally, the other is pressing or pulling vertically, and thus the operation of turning goes on with nearly uniform intensity ; the first 'man working in the least favourable position when the other is working in that which is most so. [Wrxm.Ass.]