1152

THEORY AND PRACTICE OF ENGINEERING.

Book II.

E is shown in gear, while F is clear of the cog-wheel D, and at the turn of the tide thewheel F is let into gear, and E is thrown out; this is effected by the lever G whose fulcrumis at H, the other end being suspended by the rack K, which holds the pinion on the same

SECTION OF WATER-WHEEL

axle as the wheel M : into this wheel plays the pinion N, and the winch, O, on the other endof the axle, enables the attendant to elevate or depress the wallower wheels as required.

When the tide is flowing, after the mill is stopped a sufficient time to gain a moderatehead of water, it is admitted upon the wheel through a sluice at Q, and the tail water runsout at R. The hydrostatic pressure of the head of water acting against the bottom of thewheel frame S, and at the same time between the folding gates T, W, which are thus con-verted into very large hydrostatic bellows, buoys up the wheel and frame, and mountsthem higher and higher, so that the wheel is never drowned in the flowing water, whichcannot escape under the wheel frame, being prevented by the folding gates, which passfrom one end to the other of the wheel. The wheel and frame are thus buoyed up by ahead of 4 feet, and the mill works with a head of 5 feet, or a little more.

When the tide is ebbing, and the water is running from the reservoir into the Thames,it might be supposed that the water-wheel would gradually lower with the subsiding of thewater; but to prevent this there are strong rack-works, of cast-iron, by which the wheelframe can be either suspended at any height or let gradually down, so as to give the waterreturning an advantageous head upon the wheel: the sluice R is then shut, and V openedas well as X, the water enteringat X, to act upon the wheel,and flowing out at R.

At each end of the water-wheelis a vertical shaft with wallowers,and a first cog-wheel, as F andE, and each of the vertical shaftsturns a large horizontal wheel,at a suitable distance above thewallowers, while each horizontalwheel drives four equal pinionsplaced at equal or quadrantaldistances on its circumference,each pinion having a verticalspindle, on the upper part ofwhich the upper millstone of itsrespective pair is fixed. %

The vertical shaft at each endof the water-wheel rises and fallswith it, but the large horizontalwheel, which drives the ma-chinery, remains always in thesame horizontal plane, and incontact with the four pinions.

Fig. 1746.

DRYDBN’l 1IDS-WHBEL.