Revolving Tide Mills

Revolving tide mills are tide-mills, in which the axle of the water-wheel neither rises nor falls, and in which that wheel is made always to revolve in the same direction. A water-wheel of this kind must, manifestly, at the time of high-tide, be almost, if not entirely, immersed in the fluid ; and to construct a wheel to work under such circumstances is, obviously, a matter which requires no small skill and ingenuity.

The first person who devised a wheel which might be turned by the tide, when completely immersed in it, were Messrs. Gösset and De la Deuille. Their wheel is described by Belidor in nearly the following terms:

Suppose G H (see above, fig. 107) to denote the surface of the water at high-tide, the line L M the surface at low-water, and that the current follows the direction of the arrow N ; the problem is to construct the wheel so that it may always turn upon its axis IK. The figure just referred to is a profile of an assemblage of carpentry, which must be repeated several times along the arbor, according to the length which it is proposed to give to the float-boards ; and the planks or plates which compose these floats, must be hung to the other parts of the frame by as many joints as are necessary, to enable them to sustain the impulse of the water without bending.

The sole peculiarity of this wheel consists in hanging upon the transverse beams in the frame-work, by hinges, the planks which are to compose the float-boards ; so that they may present themselves in face, as D, D, D, when they are at the bottom of the wheel, to receive the full stroke of the stream; and, on the contrary, they present only their edges, as A, A, A, when they are brought towards the summit of the wheel ; hence, the water having a far greater effect upon the lower than the upper parts of the wheel, compels it to revolve in the order of the letters ; instead of which, if the float-boards werfi fixed as in the usual way, the impulse of the fluid upon the wheel would be nearly the same in all its parts, and it would remain immovable.

We see, at once, that the boards D, D, D, having moved towards M, then begin to float, as at E, E, E, and more still at F, F, F, but that it is not till they arrive at A, A, A, that they attain the horizontal position ; after that, having arrived at B, B, B, they begin to drop towards the beams to which they are hooked, and as soon as they have passed the level of the axle I K, the stream commences its full action upon them, which it attains completely between B, B, B, and E, E, E, and this, whether the surface of the water be at G H or at L M ; for even in the latter case it is manifest that the float-boards are entirely immersed when in the vertical position P Q. Belidor says, he was present at the first trial of such a wheel at Paris, and that it was attended with all the success that could be desired.

Dryden's Tidemill

A water-wheel has been lately invented by Mr. Dryden, which will work when nearly immersed in the water of a flowing tide. Fig. 108, to the right, is an elevation of this wheel, its upper parts being supposed to stand a foot or two higher than the tide ever rises ; the axis of this wheel remains always in one place, and the wheel will work at high-water when the head is at B, and the tail-water at the dotted line A ; it will also perform nearly the same work when the head is at C, and the tail-water level with the bottom of the wheel.

The floats are all set at one and the same angle, with the respective radii of the wheel, as may be seen in the figure, and are made ao as to have an opening of at least an inch between each float and the drum-boarding of the wheel. This opening is intended to prevent the wheel from being impeded by the tail-water; for as the bucket rises out of the water, there can be no vacuum formed in it, there being a full supply of air, in consequence of which the water leaves the wheel deliberately. 1 he case is different with regard to wheels made in the common way ; for if such are open wheels, the floats are made in such a manner as to throw the tail-watei if they are immersed any depth in it ; or, if they are close, the wheel wants proper vent for the air to prevent the formation of a vacuum in the rising bucket, or what is called by the miller " sucking up the tail-water."

At D is planking made circular to fit the wheel pretty close for rather more than the width of two floats, so as to confine the water nearly close to the wheel. E, F, G, H, are sluices which are all connected together by the iron bar I, and lifted with the assistance of the wheel, two pinions, and a winch, the first pinion working into the rack; these sluices are merely for stopping the wheel when occasion requires, although one might be sufficient to supply the wheel. The rings of this wheel may be made either of cast-iron or of wood ; the floats may be iron plates rivetted together. The flanches on the arms of the wheel, exhibited in the sketch, are intended to facilitate the fixing of the first cog-wheels ; the ring of the wheel may be fixed to the flanches at the extremity of the arms, and the large flanch made fast to the axle will receive the middle part of the wheel.