Chap. XI.

MECHANICS.

991

Fig. 1467. aa is a fixed rule furnished with a row of pins, bbis a bent axle, cd a rule whose extremity c is engaged between dtwo pins of the rule a, while its extremity d, terminated by a ring, *——i

enters the bent part of the axle bb , in such a manner, that when j ^

this axle turns, the rule cd has a motion composed at the sametime of rectilinear and of circular alternate: by this compoundmotion each point of the rule cd draws a curve, which is more orless of a long heart shape, whose point is always towards thefixed rule a a : n is a square plate furnished with a ratchet-wheel;this piece may be fixed to any point of the rule cd, and ought toturn freely round an axle which passes through the centre of theratchet-wheel: fg is a piece known by the name of wolf’steeth; this wolf’s tooth is terminated by a ring which fits thebent axle b , traverses another ring/fixed at the point of the rulecd ; and this ring being movable around its axle allows the wolf’stooth to oscillate round the axle b in such a manner, that at eachturn the wolFs tooth makes a double oscillation, and is terminated Fig. 1467.at ik by a curve constructed in such a manner, that when the ex-tremity d of the rule cd is in the point of its course most distant from the pins, betweenwhich its other extremity c slides, the extremity k of the tooth will have given tothe wheel n a slightly circular motion round its centre; after having engaged one of theteeth of its circumference, the same effect should be successively reproduced at each revo-lution of the axle e, by the action of the wolf’s teeth on the other teeth of the ratchet-wheels. It is used for polishing glasses.

Continuous motion according to a given curve with a uniform velocity , orvariable according to a given law , may be changed into a given curve , witha velocity of the same nature as that of the motion which produces it, con -stant or variable according to a given law, in the sajne plane or i?i differentplaties.

Fig. 1468. Pantograph by Langlois. — By its means we draw allkinds of similar figures, changing its size at pleasure with velocitieswhose ratios are given.

Fig. 1469. Another method : let M G be a portion of the axle com- Fig. 1468.

prised between the two puppets c,p, ____

which it is required to cut; we sup-pose that the part A G of its prolong-ation’is cut in a screw shape; thisprolongation of the axle M G is sus-tained by the puppet q: the screwM G enters the niche S, and cannotturn the rule; A B is conducted bythe nut S, which turns freely roundthe point a it has a horizontal slitwin, in which the fixed cylinder centers; the rule CD slides betweenthe openings practised in the threepuppets r, p, and q ; it carries thetool K, and the perpendicular branchL G, from one of the points ofwhich a small cylinder a rises,which enters the slit mn of the ruleA B: if we turn the axle a , thenut s will proceed towards G, and willdraw with it the bar C D, consequentlythe tool K will have a velocity whichmay be varied at pleasure.

Fig. 1470. Machine for cuttingScrews . A, the cylinder to be cutinto a screw; it is sustained by twopuppets F and G; it is terminatedat A by a toothed wheel C, and thepower which turns it is applied at itsextremity A. The axle B is per-pendicular to the cylinder A ; it issustained by the two puppets H andI, and carries a toothed wheel D, whichengages the wheel C; the part gh of

Fig. 1470.