The represented in Figure 2, is also of cast iron, but is provided with wooden floats or paddles laid across the periph ery of the wheel. To retain the water as long as possible in the spaces between the paddles, a circular channel (A,B,E) closely encompasses a portion of the wheel. This channel is not required for overshot-wheels, but it is an indispensable part of high breast- and middleshot-wheels. It is constructed either of wood, as in this example, of iron, or of masonry. The sluice-gate, which is secured to a pivoted horizontal rod, is adjusted by a rack and pinion D). Instead of allowing the water to run in between the circular channel and the bottom of the sluice-gate, as in Fig ure 2, there is employed a so-called "overflow" sluice-gate, which shuts off the water•on the bed of the channel and forces it to pass over the gate (A/. 63, jiAr. to). The construction of the wheel in Figure m is very nearly like that in Figure 2 (A/. 62), it having, however, wooden shrouds and wooden anus set in cast-iron hubs, and for transmitting its power is fur ther provided, like Figure 4, with a cog-wheel, which is supported by radial rods.
Poncelet circular channel of under shot-wheels is necessarily short or is entirely omitted; otherwise their external appearance is generally the same as that of a middleshot-wheel ( jig. 2). Figure 4 (A/. 63) exhibits a peculiarly-constructed wheel (called the " Poncelet wheel " after its inventor) which in this case is of iron and provided with curved plate-iron buckets so constructed that by the aid of the sluice-gate the water is forced to impart to them almost its whole force by impact. The water is directed down a slope or curved race and enters the wheel with the full force of its current. Gliding up the curved buck ets, it comes to rest, falls back, and at the point of discharge acquires a backward velocity nearly equal, relative to the wheel, to the forward velo city. The diagrammatic lines drawn ou the lower part of the wheel, which is shown as cut away, are intended to illustrate the action of the water iu the latter respect.
Zuppinger's more recent construction—designed, however, for a greater height of fall—is Zuppinger's wheel, shown iu Figure 3 (p. 63). It consists of a single rim (A, B) and of long radial sheet-iron buckets, which are secured on one or on both of their sides, but are enclosed top and bottom by a casing (D, E, F, G, H, K). This casing, which admits the water sidewise into the bucket, prevents its escape until the buckets have reached their lowest position (H, G), thus securing a high degree of effect.
Sagebien's II/heel (figs. i, 2) is designed more completely to utilize
the power of the water by receiving its entire momentum without loss of the height of fall—that is, without lowering the head surface of the water. Externally, Sagebien's construction somewhat resembles the Poncelet wheel (fig. 4), the water in the former, however, being admitted over an overflow sluice-gate. As, in many cases, this form of construc tion involves the use of very large, and consequently expensive, wheels, the inventor devised the wheel with a smaller diameter, shown in the Figure, which is nevertheless also rendered costly through its complicated structure. As will be seen from the plan (fig. 2), the water, instead of being admitted to the periphery, flows in on both sides of the wheel. To secure this object the paddles receive a peculiar construction, and, though rather expensive, have the advantage of completely utilizing the power of the water. The elevation (fig. 1), which exhibits the upper part of the head race in section, will convey an idea of this method of constructing the paddles. The moving water, moreover, can be admitted to one or to both sides of the wheel, as desired, by opening one or both of the sluice gates placed in the fork of the channel.
Floating a substitute for the current mill-wheel Professor Colladon of Geneva invented what may be called a "floating" current wheel 62, fig. 3), which consists of a circular iron body or drum pro vided on the outside with paddles. The drum, being hollow, floats on the surface of the stream and is rotated by the running water. The manner of setting the wheel and of connecting it to the machinery it is intended to drive is as follows: The pillow-block for the transmitting shaft leading to the bank of the river is placed in a frame of beams, whose lower ends are secured in the bottom of the river. Extending horizontally from this frame are two movable cast-iron arms, between which is arranged the cylinder-like wheel. Ou one of the arms is fixed a centre gear-wheel, which engages with the spur-wheel of the drum and with the cog-wheel of the transmitting shaft; hence it will be seen that, notwithstanding the rise or the fall of the water-wheel with every fluctuation of the water-line, no injury results to the transmitting shaft by reason of its fixed position. The inventor has also placed a floating race under the wheel. The cross section of the current of the stream being reduced by means of the race and the submerged frame and water-wheel, the velocity of the water is con siderably increased, whereby a higher degree of power is obtained.