Chap. XI.

MECHANICS.

965

Fig. 1S65. a 6 is a crosspiece pierced with a groove, inwhich the axis of the toothed wheel e may move freely ; c isa bar furnished with teeth which engage a wheel, andwhich is fixed to the rule to which the alternate motion ina right line is to be given, sliding between the two tenonsd,d. When the toothed wheel e has arrived at the end of itscourse, the obstacles n, n meet the springs to force it to returnand engage afresh.

Fig. 1366. a is a crown wheel, whose interior is toothed ;b, a circle also toothed, whose diameter is equal to the radiusof the crown with which it engages. The crooked axis turnsin the centre of the crown, sustains on one side the centreof the wheel 6, and on the other a handle to the powerwhich communicates the motion of rotation to the wheel b.Whilst this wheel turns round its centre, passing over thecontour of the crown, each of the points of its circumferencetraces a diameter of the crown.

The two teethed wheels a and b produce an alternatemotion, the number of whose alternations, their extent andvelocity, may vary to infinity, either by the different ratios of

Fig. 1365.

Fig. 1369.

Fig.1367.

Fig. 1368

Fig. 1370.

their diameters, or by the different arrangement and proportions of their parts, but allthese movements may be exactly imitated by fig. 1349. Figs. 1368. and 1369. exhibit thesame motions.

Fig. 1370. is a circular crown furnished with teeth on both its concave and convex sides :it is fixed to a large circulardisc </, which turns on its axis,leaving a part void, so that thetoothed wheel d can passfreely ; it is terminated by twoportions of arcs of circles alsofurnished with teeth. Thetoothed wheel d turns roundits axis, which has the facilityof moving in the groove mn.

The two springs leaning alter-nately on the two stops de-termine the alternate circular motion of the disc d. The alternate circular motion of thedisc d serves as an intermediary, communicating to the body another alternate rectilinearmotion by means of an endless cord, which envelopes the disc and passes through the twopulleys s,t

In this figure are united two well-known methods oftransforming circular continuous motion into alternate recti-linear, either by employing a bent axle, or a circlewhose plane is inclined to its axis of rotation. The hydrau-lic wheel causes the vertical axis to turn : this axis carriesa circle whose plane is inclined to it; the vertical rods of thepiston have catches or stops furnished with friction rollers,and lean on the edge of the surface of the inclined circle;thus the circular motion of the vertical axis of the hydraulicwheel communicates an alternate rectilinear motion to the pistonrods; the rods of the piston are maintained in the verticalposition by grooves furnished also by friction rollers; a doublecatch, viz. one which applies itself against the lower surface

of the circle serves to aid the piston in its descent, and renders the motion more uniform,

3 y 3

Fig. 1371.