966
THEORY AND PRACTICE OF ENGINEERING.
Book II.
Fig. 1372.
Fig 1373.
Fig. 1374.
The great wheel r (fig. 1372.) turns round its axis; its surface is furnished with threerollers, on which the roller q successively leans, at the end p of a lever pgh , whose arms makea right angle; the other end tendsto turn by the action of a springor weight the lever p towards h; theextremity h will have an alternatecircular motion, which will bechanged to alternate rectilinear bymeans of the pulley f
s (fig. 1373.) is a fly-wheel fur-nished with a pinion ; p and r arcteethed wheels engaging each other;p also engages the pinion: twowinches are fixed to the axis of thewheels p, q : mf, m g , are two rodswhose ends turn freely and com-municate to the rod pr an alternate
rectilinear motion, while the fly s turns circularly in the same direction ; reciprocal motionis -also obtained by this arrangement; it is applied to engines or pumps.
a is a toothed-wheel put in motion by the pinion 6, whichobeys the immediate action of the mover; the weight is sus-pended to the extremity of the cord </, which passes througha pulley, and is rolled on the axle c of the wheel a ; t is thegudgeon of the same wheel. The brake consists of a leverturning on the axle of rotation; it is furnished with a concavepiece p t which should apply itself to the axle r, and a counter-poise A, which serves to raise it as shown in the figure; theobstacle r maintains the break in this position : when it is re-quired to discharge the weight suspended by the cord d, thepinion 6 is drawn from the toothed-wheel a ; the weight falls,and when it is 3 or 4 feet from the pavement, where it wouldbe broken, the extremity m of the lever is heavily pressed,and the piece p by its friction on the axle c immediately stops its velocity,
Let a be a drum fixed to the axle of the machine, furnishedwith a ratchet-wheel turning in the direction indicated by thearrow; m is the lever of the brake, c a catch suspended by acord at the extremity of the lever 6 which turns from the point,and leans on the small pulley at the extremity of the brake m :the piece e prevents the catch from mounting by means of asalient point, while the spring tends to approach the ratchet-wheel, and by its curvature sustains it when it is in motion ;when the motion becomes retrograde the catch is drawn back,the brake acts, and the machine is stopped without shaking,and consequently with the least possible inconvenience.
Wheels used at the Stone Quarries , Paris. — A large beam q turns round a fixed point, andsustains on one side the wheel a, and
on the other a counterpoise p capable of a
lifting the wheel a; the whole forms asystem similar to the Roman steelyard,loaded with a weight whose place is heresupplied by the wheel a; and the run-ning weight is replaced by the counter-poise/), capable of lifting the wheel a.- beis an upright,/c a beam which turns rounda point yj and which carries the brake q;ed a rod of wood or metal turning roundthe axes of rotation e and d; nn the cordwhich serves to draw up the stones fromthe quarry; pr a ratchet-wheel fixed tothe axle-wheel a, with its catch v fixed tothe upright be; on the other side of thewheel a should be another upright gh t tosustain the other axle of rotation of thelever g, which should have the form ofa fork in which the wheel a enters, andwhose sides should leave the space neces-sary for giving it a free passage. Thestone to be drawn up is attached to one
Fig. 1376,