970
THEORY AND PRACTICE OF ENGINEERING.
Book II.
pleasure to a wheel the action of the mover, which causesthe axle to turn on which the wheel fits; and reciprocally,we can by this mechanism communicate to the axle, or sus-pend at pleasure the action of the mover which drives thewheel. Prony caused a great horizontal wheel, a b, to turnby the immediate action of the mover ; this wheel puts inmotion in contrary directions the two vertical wheels c and d ,which work into the horizontal axle ef whose interior faces allengage a ratchet-wheel at nm . At one of the extremitiesof this axle is a pulley, g, round which a cord is wound, havinga bucket at each end; a piece, a a, formed by two iron bars,which carry a ratchet-wheel, pg, at their extremities, slidesalong the square axle ef by means of coupling boxes, alsocut square ; it is evident that if the piece a a is pushed towardsthe extremity e of the axle ef, the ratchet wheels g, n will en-gage, and the axle ef will turn in the same direction as thewheel d; if it be pushed towards the extremity f the axle willturn in the direction of the wheel c, and one of the bucketswill ascend while the other descends. Alternate motion is communicated to the piece a a,in such a manner that it takes place immediately after the ascending bucket is emptiedinto the trough, and the cord of the bucket itself determines its motion. For thispurpose under the axle ef another horizontal axis, ss, was placed in a direction perpen-dicular to ef; this iron axle ss is furnished with a catch, x , which enters the slidingboxes of the piece a a by a rod, h , terminating by a weight of 1 *ad, p, and by two claws,s, t; two knots or forks are placed towards the extremity of the cord above the bucket, soas to engage successively the two levers m,n. These levers act on the claws $t, and raisethem, so that the rod h passes the vertical position at the moment when the ascendingbucket is emptied ; then the weight p causes the axis ss to turn briskly, and its catch xdrives the piece aa towards the same side, and maintains its position, and makes theratchet-wheels act; the axle ef turns in a contrary direction, and so on, &c.
Fig. 1386. shows Prony’s method of unharnessing an animal employed to drive thismachine when the effort was increased by any cause. Three traces, 1,1, 1, pass throughthe openings 2, 2, made in the yoke 4 4, attached to the end of the lever 3; this leveris fixed to the vertical axle, which gives motion to the machine; the openings 2, 2, arefurnished with pulleys to diminish friction : the extremityof each trace terminates in an eye, which hooks on to a screwring, fixed in the axle 5, movable in gudgeons; round thisaxle 5 is wound a cord, which ascends, passing through thepulleys 6,6, and attached to a weight along the verticalaxle ; this weight, which may be varied at pleasure, determinesthe resistance opposed to the effort of the animal. Sup-posing the weight limited to 20 pounds, and a stick falls intothe teeth of a pinion, it would follow that by the effort ofthe animal the machine would be broken; but, as the effortwill necessarily exceed the weight, which serves as a regu-lator, the axle 5 will be obliged to describe a quarter circle.
The screw bolts having then quitted theii vertical position,the extremity of the traces hooked thereto escape, the animalis freed, and the mechanism avoids injury.
Fig. 1387. ab is an axle turning on its axis by meansof a power applied at a; its pivot b rests on a piece of woode , furnished with two rollers, which enter a groove inthe cross piece nm. By this means the axle ab may easilyapproach successively the toothed wheels o,o , to w'hich theendless screw h, with which it is furnished, engages. v,vare two cross pieces, which serve to sustain the axle, withoutaffecting the slight balancing motion which ought to becommunicated to it by the movable piece e , on which itspivot rests. In this piece are two catches, which turnround their two axes, which, as well as the two pins attheir extremities, are prolonged; this piece has an axle,having two other branches cut in the form of a fork, toallow the cord which carries the bucket to pass; near theextremity g a rod rises, carrying a weight p. In the crosspiece nm are seen two screw rings, x and y, whose pro-jection equals the thickness of the two catches ab, cd.
Two buckets are attached to the extremity of the cord,
Fig. 1386,