968

THEORY AND PRACTICE OF ENGINEERING.

Kook II.

roller, and the ram rises along the post vv; when the latter arrives at its greatestheight, a man placed at the end « of the bar leans on the end i of the lever, and lowersit; then the point of the roller escapes the claw of the lever which retained it, and the ramfalls ; the lever is then let go and raised by the spring, and lays hold of another pin, whichjoins the roller to the capstan afresh. There is a great friction in this method.

Fig. 1380. is an iron axle, turning always in the samedirection, either by the action of men who act on the bar of acapstan, or by the effect of any other mover ; it traverses thetwo wooden drums a and 6 which are attached to the axleby gentle friction ; the lower drum a rests on the plank, andis furnished with two upright surfaces, one outer, the otherinner, each making one turn of its circumference spirally ; thesesurfaces are so situated that their extremities are at the twoends of the same diameter; the same drum a is furnished witha ratchet-wheel r, and a catch which prevents it from turning inthe direction of the mover ; the upper drum b is hollow in itsinner part, and furnished with two vertical rods, which carrytwo rollers, the height of which is equal to that of the lower

Fig. 1380.

drum ; it is sustained by these two rollers on the inclined planes of the drum a, preservinga horizontal position, it also carries a bar of iron t, terminated at the height of its lowersurface, and its convex surface is cut into a groove to receive the cord of the ram. Whenthe roller fixed on the rods is at the beginning of the inclined plane, the drum b is at itsmaximum of descent, and if the latter is turned in a direction contrary to that of themover, the roller would meet the two heads of the upright surfaces, and would compelthe drum a to turn equally, but if b turns in the direction of the mover, a would remainimmovable, and 6 would elevate itself vertically, turning by means of the two rollersto the height of the two surfaces on which it is situated. The iron axis p has a strongiron cross piece t placed in such a manner that it touches nearly the upper part of thecavity of the drum 6 when the latter is as low as possible. Supposing when the drumb is at the maximum of its descent, the bar i in contact w’ith, and ready to act on the pointt; the ram m on the head of the piles, and the cord d stretched, the axis p by itsmotion will turn b , which will elevate the ram to a height equal to its circumference; thenthe bar of iron t escapes the cross-piece i, and the drum b yielding to the action of the ramm. turns in an opposite direction, and allows it to fall, consequently the drum b will have analternate circular motion, while the ram m will have an alternate rectilinear motion, and thespace which it goes over in this case is equal to the circumference of the drum b.

Fig. 1381. a b is an axis which the powercauses to turn always in the same direction;the wheel c acting in a groove, enters into theaxis a b by gentle friction, but without beingable to slide along and on one of its facesa pin s is fixed: nm is an elastic bar fixed tothe axle; r is an inclined plane placed nearthe circle e , and in the direction of its plane.

The cord ct has one of its extremities fixed inthe throat of the wheel e, and the other to theflail pq , which turns round its axis p. Whenthe axle a b turns, the elastic bar nm meetsthe pin s, and obliges the circle e to turn also,which lifts the flail pq. But the bar nmmeeting the inclined plane r retires from thecircle e, and allows the pin s to escape; the circle is then abandoned to the action of theflail, which falls and goes on as before.

It is not possible to describe all the methods by which motion istransformed or converted ; to do so, it would be necessary to analyseevery species of machine that has been invented: to illustrate the moresimple means which have been resorted to, in connecting the first with thesecond mover of a machine at the impelled point, and the last actionupon the working point, is all that we aim at describing ; mechanistshave devised many ingenious contrivances for particular purposes, butthe whole of which it would be impossible to describe.

Fig. 1382. is applied to a machine for beating plaster, &c. The piecea is fixed to an axle turning always in the same direction, and the wheelb is boxed on the same axle with gentle friction, in order that it mayturn in contrary directions; this wheel is furnished with a catch c towhich the piece a hooks, which thus causes the chain d to mount, towhich one of the pistons is attached.

Fig.1381.

Fig.13*2.