Hori:onlal construction of the wind-wheels thus far described exhibits on comparative review a similarity to that of certain transport machines for water and for air; they may also be compared with several makes of centrifugal pumps and with a few forms of ventilators, of which, for example, that shown in Figure 7 (p. 'IS) has vanes like those of a wind-wheel. Certain other motive machines also resemble wind-wheels. The turbine-wheel of Henschel's system (pi. 66, fig. 6) consists of a number of oblique or helically-curved blades grouped around a shaft in the form of a wind-wheel. These surfaces form the principal constituents of the wind-wheel as of the turbine, they being in the first the receivers of the motive substance air, and in the latter of water.
It is natural that such comparisons should suggest the idea of other forms of constructions for aerodynamic purposes. To these belongs the so-called " Francis turbine " 65, jig. 6), which is moved by the water acting on the periphery of the wheel. If the casing of this turbine were removed, so that only the guide-wheel and the turbine-wheel remined, we should have nearly the form which has been, and still is occasion ally, employed in the construction of windmills. The wheel-shaft, as in the turbine, is placed vertically—an arrangement which obviates the neces sity of setting the wheel in the direction of the wind and of employing the vane and its auxiliary mechanism. From whatever direction the wind may come, it strikes one half the wheel; so that in any case the directrix upon one-fourth of the wheel transmits the wind-power to the turbine, while the directrix upon the other fourth deflects the wind and prevents it from exerting an opposing influence upon the rotation of the wheel. Wheels with vertical shafts are called " horizontal " wind-wheels, because they rotate in a horizontal plane.
Field's Horizontal 3 and 4 (pl. 72) exhibit two forms of horizontal wheels. In Field's horizontal wind-wheel (fig. 4) the whips or wheel-arms E, which are fastened on the vertical shaft B by means of a hub (D), are supported by the connecting-rods g secured to the verti cal shaft and are stiffened by the rods h. The arms carry on their extrem ities four frames (F), which form the bearings for the cranked shafts I, and to the latter the vanes G are attached. If these frames were simply cov ered with sail-cloth, it is evident that the wind would strike those vane surfaces which in the course of their rotation must move against it as forcibly as it would strike those surfaces which the wind is to move, and in consequence the wheel would come to a stand. A mechanism must, therefore, be provided which will so operate that the vanes to be moved in the direction of the wind will present their full planes to its force, and that the vanes moving in the opposite direction will present as small sur faces as possible. Such a mechanism is formed by the cords I, which are
loaded with the weights TV and conducted from below the hub D, along the under side of the whips, over the pulleys on the outer ends of the oblique arms and attached to the cranks of the vanes G. As these revolve, the wind, acting on their broad sides, lays the vanes flat against their frames (thns raising the weights), where they are held by and exposed to the full force of the wind. On moving farther the vanes are swung around by means of the weighted cords so as to feather or present their edges until they again into position in the direction of the wind. By means of a hand spider-wheel (-11) the weights IV can be lifted, whereby the cords arc relaxed, the vanes arc liberated, and the wheel is brought to a stand. The construction shown in the Figure is evidently simpler titan the vertical wind-wheel, as both the mechanism of the wind-vane and the bevel-gear connection of the horizontal and vertical shafts are omitted, the wind-wheel being directly connected with the vertical driving-shaft, which for the transmission of the power needs only to be provided, on its lower end, with a cog-wheel (C) or a pulley or a crank, as may be needed.
ins Iior1;ro1l!ul II simplest form of wind-wheel is perhaps the construction of the Goodwin-Hawkins wheel, shown in Figure 3 (p/.72), in which the adjusting mechanism is also omit ted. In a hollow column (A) is placed the shaft 11, which by means of anus carries six hollow cones of metal. These by aerodynamic or hydraulic law possess the property of receiving a greater impetus from the wind strik ing their concavities than from its acting on their convex surfaces; hence, with a current of wind in the direction from right to left, parallel to the plane of the illustration, the cone C nearest the observer is more forcibly affected by the impulse of the wind than the cone on the opposite side, and from the difference in these forces the rotation of the wheel is accom plished. Even if the wheel be provided with a mechanism to regulate the varying velocity of rotation, which, as in this case, where a pump is to be driven, is regulated by the height of tile water in the reservoir J, the con struction of this horizontal wheel is simpler than that of a vertical wheel. The reason that wheels of this form are not preferred is because with an equal size they are less affected by the wind than vertical wheels—in other words, they must for the performance of a certain desired effect be larger than the latter—and hence, notwithstanding their simplicity, they are more expensive under otherwise equal conditions than vertical wheels for the same purposes.