Chap. XI.

MECHANICS.

$71

Fig. 1388.

Fig. 1389.

which passes over the cylinder of two toothed wheels o,o,making a turn round each. In the position represented bythe figure, the branch u, after having pushed the pin a 1towards the left, makes the endless screw A engage thetoothed wheel, and the catch a'V y falling by its own weight,engages the pin x y and drives the axle against the toothed wheel.

When the button $, which is near the bucket g, has engagedthe fork /, the piece u is obliged to turn on its axis, and thearm n, touching the pin b , unhooks the catch, in order toassume a horizontal position ; but it has scarcely passed thisposition when the counterpoise, p , falling on the other side,the arm u pushes the pin, and causes the axle to pass to theright, which engages the wheel o, while the catch cd by itsown weight engages the pin y. The two cylinders turn incontrary directions, and the bucket q descends, while the othermounts; the edges of the buckets are furnished with a pieceof iron, to oblige them to assume a situation proper foremptying the water. This machine was the invention of M.

Belancourt.

Fig. 1389. — In proportion as the circular motion of theaxle a b increases or diminishes, the weights p and q retirefrom or approach this same axle, by virtue of the centrifugalforce; and the crown r, which embraces the axle, descends orascends vertically. On this crown the motion of a valve independs, which prevents the steam from introducing itselfinto the cylinders of steam-engines, or of escaping fromthem to pass to the condenser, and by this means the machine

preserves an almost constant velocity, although the resistance may be variable. We haveseen it applied to a windmill to raise the revolving stone when the velocity was too great,to prevent the flour from heating.

The revolving stone a receives its motion at the upper part,as is the case in all windmills; this stone is carried bythe axle, which rests on the sole plate fixed to the bearer.

In the axle is fixed the crown fg, which carries four armsto receive the rods of the four iron balls, h, *, k , L, each 4or 5 pounds weight; from the upper parts of these rods fourbraces descend, which support the piece m, which slidesfreely from the top to the bottom of the axle ; in this piece agroove is cut to receive the extremity of the lever de, of aforked shape, whose other extremity 0 supports the bearer,which turns on the centre n ; it is evident that by the motionof the revolving stone, the whole system of balls will revolve,and that in proportion as the velocity of the wind increases that of the stone, the ballswill fly off from the axle, the piece m will descend, force the lever de into the part d, andwill lift the bearer, and consequently the upper millstone a.

Fig. 1391. Change of alternate rectilinear motion to continuous circular .— Tide Mill,a is the axle of the wheel turning on an iron pivot oraxis ; bb are the wings of the wheel, a little inclined,to allow the water to pass in a spiral direction ; cc is •a drum or circular envelope, in which the wheel turnsin the least possible space between its sides and its floatsdd,dd. A second drum of a larger diameter is placedabove the wheel, and crowns the drum cc with which itis combined; ee are movable doors which open on op-posite sides; the first, on the side of the current, openswhen it is pressed by it, and is arrested by the postf The door on the opposite side will be pressedby the current in the opposite direction, and will close.

The inverse operation will take place when the waterwhich shall have mounted by the flux attempts to re-tire at the instant of the reflux. The dotted lines alsoindicate this contrary motion.

Suppose the surface of a river A, which at low wateris level with the cover of the upper drum, in order thatthe same quantity may always act on the wheel; whenthe surface of the water is above the circle of theupper drum, the water which passes above will not pro-

Fi^ 1390.

Fig.1391.