Chat. X I.

MECHANICS.

969

When the extremity of the catch has leaned against the pin or stop e , the piece a unhooks;the piston suspended to the chain d descends by its own weight, causing the wheel b to turn.

To change motion at intervals, the Catch- Wheel b , mounted on an axle, receives the motionof rotation by the assistance of a handle.

Fig. 1383. a is an axle which wc suppose to be turning con-stantly in the same direction by the action of any power : c acircle or toothed wheel, which enters the axle a by gentle fric-tion, and which has two mortices to receive the pins ; d isanother circle which fits the portion q of the axle a, which, in-stead of being cylindrical like the rest of the axle, is quadrangular.

In this circle are attached two small pins by means of a fork.

The circle d may be made to advance and retreat at pleasure. j,/ ]3s3The machine being in the position represented in the figure, the

circle c may remain stationary, or may obey the action of the mover, which turns it in adirection opposite to that of the axle a. We may regard it as absolutely independent ofthe motion of this axle, except the slight friction which it experiences towards its centre.But if by means of the fork we bring the circle d to the circle c, so that the mortices meetthe salient pins; the wheel c necessarily obeys the action of the axle a, until we are againobliged to draw the wheel d away, and so on. The spring e tends to draw away the collard from the toothed wheel c, in order to remove it from the action of the mover; the catchhere shown in plan and section turns round the axle i ; the obstacle b on the one hand, thespring k on the other, determines the position and extent of its motions; if we turn the leverso that the communication of motion takes place, the catch s will be arrested by thespring e. When we wish to suspend the action of the mover on the machine, we must pressslightly on the extremity t of the catch ; the spring e will act on the extremity of the lever,and the collar d will retire from the wheel c, on which the mover has no more action. Bythis mechanism the motion of a machine may be stopped, first at any given hour, secondly,in mills when the corn is ground, thirdly, in looms when the shuttle is stopped in its course.

The first case offers no difficulty ; it suffices to make the weight of an alarum act on theextremity t of the catch to render it perceptible.

In mills the motion may be stopped when the grain has run out, profiting by the samemechanism as is employed in this case, to call the attention of the miller to remove the catch.

It often happens in looms for weaving that the shuttle is arrested by a thread breaking, orsome other cause, to prevent the disorder which would result in this case, it must be recol-lected that when the batten is driven from the side of the weavers’ beam, on which the warpis rolled, the shuttle is driven by the blow which it receives from the shuttle driver;the batten immediately returns towards the small working beam, to strike the woof, andthe batten whose section is given goes with an alternate circular motion over the arc ab ,whose centre or axis of rotation c traverses the sole of the weaver’s frame. This motionshould not be uniform, but slackened towards the extremity a of the arc a b, which we sup-pose to be that on the side of the great beam, to allow the shuttle time to pass from oneside to the other to the batten, whatever be the size of the loom, and it should be moreor less accelerated towards the extremity b of the same arc, to strike the woof. We mustimagine an iron rod placed along the batten, and turning freely on the axle p, furnishedwith a bent lever at each of its extremities, and tending by the action of a spring, placedabout the middle of its length, to turn in opposite directions, so that the levers resumetheir original position.

It will be seen that if the shuttle was not arrested in its course, the lever would notmeet the obstacles a,c when the batten by its circular alternate motion passes over the arcab to strike the woof; but in the other case, viz. when it is stopped by any obstacle, thelever will then meet the point a, which yielding to its action will descend, and actingon the extremity t of the catch will separate the collar d from the wheel c, and in an instantafter it will meet the invincible obstacle b, the action of the mover will be suspended, andthe batten cannot strike the woof; the objects which were proposed will then be answered.

Fig. 1384. is a further modification of the precedingmovement. ab is the axle which turns in the samedirection with the action of the power ; the wheel c transmitsthe motion to the wheel d, which fits by gentle friction onthe axle ef; the wheel d is furnished with a pin, and the axleef with another g ; the wheel d retires or approaches thepivot q at pleasure, by means of the lever pq : it will thus beimmediately seen that we can stop or produce the motion ofthe axle ef by bringing the wheel d near, or taking it away'from the pivot g.

Fig. 1385. Prony’s machine : its mechanism only consistsof a very ingenious application of

Fig. 1383., by which we can suspend or communicate at