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APPENDIX.

Raising Water tJirough a Screw, p. 140. Some persons deceived bythe apparent facility of working a water screw, especially when its jour-nals are delicately fitted to their bearings and they turn with little friction,imagine tbat it not only elevates the liquid with a less expense of forcethan any other machine, but with less than is due to the quantity raised ;hence it has often been adopted in projects for the perpetual motion. Whenarranged so as to be turned by an overshot wheel, it constitutes one half ofthe first attempts at a solution of that impossible problem, under the im-pression that it would raise and discharge upon the wheel all the waterexpended in moving it! The inclined position of a water-screw is sup-posed to .contribute to this imaginary result, for, say these reasoners, thewater then arrives at the top by naturally flowing along each convolution,while the force consumed is little if any more than would be required toturn the tube if empty !—the fluid being thus raised in a different mannerand with much less force, than when lifted directly and perpendicularlyby the piston of an atmospheric pump, or driven up by that of a forcingone !

In these projects, the action of the wheel depends of' course as muchupon the screw, as that of the latter does upon the wheel; in other words,each is designed to turn the other : but the very idea of two machinesreciprocaliy moving each other at the same time is palpably absurd. Thetwo forces will either be equal or unequal. If they are alike both wouldbe in equilibrio, and the machines would remain at rest; and if at anytime one force exceeded the other, the same result would necessarily takeplace, for the smaller could not then overcome the greater. If the wheelcould transmit its entire force to the screw, (undiminished by resistancefrom the air, the friction of its bearings and that of the intermediate me-chanism,) it would still be impossible for the latter to return it, because todo so a greater force than that derived from the wheel would be required ;a machine cannot be moved and at the same time move its mover.When moved, its force is less than that by which it is moved ; and if itbecomes the mover, its force must exceed that of the machine to which itimparts motion.

The effect of any machinery composed of levers, cranks, wheels, &c.and moved by water, animals, or men, can never exceed the power thatmoves it, for there is nothing in wood, iron and brass, or in any combina-tion of them, by which they can create force, or, what is the same thing,gi ve out more than is imparted to them. As well might we expect to seea carriage returning of itself from a long journey, and laden with the horsesthat drew it from home.

Wilkins has given a chapter in his Mathematical Magic on “ composinga perpetual motion by fluid weights.” His prominent plan was raisingwater by a screw, and discharging it on float boards attached to the screwitself. He quotes older authors who indulged the same whim. Visionsof great mechanical discoveries often burst upon the ingenious prelate, aswell as on lay inventors: in such seasons he was in ecstacies. When hefirst thought of obtaining power by means of a water-screw, he says, “ Icould "scarce forbear with Archimedes to cry out, Eureka ! Eureka! itseeming so infallible a way for the effecting of a perpetual motion, thatnothing could be so much as probably objected against it : but upon trialand experience I find it altogether insufficient for any such purpose.”

In the Gentleman’s Magazine for 1747, p. 459, there is a descriptionand figure of a similar device—either water or balls were to be raisedthrough a screw and dropped upon an overshot wheel. It was devisedby a Col. Kranach, of Hamburgh, who, in a pamphlet, declared he had