97 2‘

THEOIIY AND PRACTICE OF ENGINEERING.

Book II.

Fig. 1393

Fig. 1392.

duce a greater effect by rising several feet, than when it was at the level of the cover, i ishows the bottom of the river, and the water enters the drum by passing the door e until itarrives against the post f; there it finds a passage, by means of which it arrives at the bottom

across the spiral floats, which yield to the impulse of the current, and give a motion of

rotation to the vertical axle. When it has arrived at the bottom, the water escapes by

the door k , producing motion when the tide is flowing out; when, on the contrary, it is

coming in, the two doors we have just mentioned close, and the two opposite ones open, bymeans of which the water descends as before, and turns the wheel in the same direction by theflux or reflux.

The advantages of this wheel over others of the same kind are, that if it be employed forcorn mills its velocity is more uniform, since the same quantity of water always acts on it;secondly, it turns in the same direction by the flux or reflux, and in a more simple mannerthan other tide-wheels ; thirdly, as the wheel is horizontal, it is easy to adapt any gear toits axle, since we can elevate this axle at pleasure above the surface of the water; fourthly,the velocity of this wheel is greater with regard to the velocity of the tide, than for otherwheels, which dispenses with all thecontrivances used in the old wheels todiminish friction; fifthly, it is moreeconomical.

Fig. 1392. is a vertical axle, verysolidly fixed : it is terminated by atoothed wheel, c. A hollow cylin-der d fits this axle, and reposes ina rebate practised on the lower partof the same axle; four cross piecesa, b, 0 ,( 1 , issue horizontally from thiscylinder, and at right angles with it; at the extremity of each cross piece is suspendeda car; on one of the cross pieces the axle of a small wheel i is fixed, which engages thetoothed wheel c. At the extremity of the small wheel i four cords are attached, eachpassing through a fixed pulley to the extremity of the cross pieces. A person seated inone of the four cars may easily communicate a continuous circular motion to the littlewheel i by means of the cord which passes through the pulley in front of it.

A is a circle whose circumference is furnished with a crown ratchet-toothed ; f, c tworules which turn freely round the axis of the wheel A ; two other rules form an irregularquadrilateral figure with the preceding, whose angles are nearly right angles: the extre-mities of these four rules are united by axles, round whichthey turn freely. A* is a rule united at A with the quadri-lateral ; an axis traverses at h the three rules; the rule A ipasses through the two tenons k and Z, and can only moveitself in the proper direction; two of the rules carry twocatches, placed, the oift to the right and the other to theleft of the figure: these two catches are attached to therule by hinges, and enter the notches of the ratchet-wheel,either by their weight or the action of a spring : let usnow suppose we can move the rule hi from h to ?, the catch m will act on the crown,and will turn the axle A in the direction indicated by the arrow, whilst the catch nwill slide on the teeih of the same crown : but if the rule return from i towards A,the catch n will act, whilst the other, m, will slide; in both cases the wheel A will turnin the same direction. 'The alternate rectilinear will then be transformed to circular con-tinuous.

Let a be a wheel furnished with six pins; qp a horizontal plank sustained by therollers b and c, with a catch de , whose length is equal to the distance between theplank and the half of the space which separates the two pins 1 and 2; fg and (/A,

forming between them a right angle, this bent lever can turn freely round the axis

of rotation g : the length of the rod g A is equal to the D

radius of the circle g ; the point g is in the line g A, ?

parallel to the rule or plank qp y and the rod hg tendsalways to descend by its weight: /is a pin which belongs tothe plank qp; the horizontal distance of this pin from thevertical, which passes through the point g , is equal to thedistance Dd. If we make the wheel a turn in the directionindicated by the arrow, the pin 1, acting on the catch d

Fig. 1394.

Fig.1396.

will draw the plank qp from q to p, while the pin 5 will restore the bent lever fgh. Whenthe pin 1 arrives at the point e it will cease to act on the catch de. The arm gf of thebent lever fg h will be in a vertical position, and will commence to act on the pin f of theplank A/j, which will return in the direction q A; when the pin 5 of the wheel a arrives atthe point 6, it will quit the arm gh of the bent lever, and lean on the pin 4, which