Within the enclosure are arranged four scrolls of suitable proportions, dipping the water, at one end, and emptying it out at the center of the wheel as more clearly shown in Figs. 74 and 75.
The Noria or Egyptian Wheel. The tympanum has been described as an assemblage of gutters, and the Noria may be considered as a number of revolving swapes. It consists of a series of poles united like the arms of a wheel to a horizontal shaft. To the extremity of each, a vessel is attached which fills as it dips into the water, and is discharged into a reservoir or gutter at the upper part of the circle which it describes. Hence, the former raises water only through half a diameter, while this elevates it through a whole one. (Fig. 77.)
The Chinese make the noria, in what would seem to have been its primitive form, and with an admirable degree of economy, simplicity, and skill. With the exception of the axle and two posts to support it, the whole is of bamboo, and not a nail used in its construction. Even the vessels, are often joints of the same, being generally about four feet long and two or three inches in diameter. They are attached to the poles by ligatures at such an angle, as to fill nearly when in the water, and to discharge their contents when at, or near the top.
The periphery of the wheel is composed of three rings of unequal diameter and so arranged as to form a frustrum of a cone. The smallest one, to which the open ends of the tubes are attached, being next the bank over which the water is conveyed. By this arrangement their contents are necessarily discharged into the gutter as they pass the end of it. When employed to raise water from running streams they are propelled by the current in the usual way—the paddles being formed of woven bamboo. The sizes of these wheels, vary from twenty to seventy feet in diameter; some raise over three hundred tons of water in twenty-four hours. A writer mentions others which raise a hundred and fifty tons to the height of forty feet during the same time.
Note.—The mode of constructing and moving the noria by the Romans, is thus described by Vitruvius, who lived about the beginning of the Christian Era. “When water is to be raised higher than by the tympanum, a wheel is made round on axis of such a magnitude as the height to which the water is to be raised requires. Around the extremity of the side of the wheel, square buckets cemented with pitch and wax are fixed; so that when the wheel is turned by the walking of men, the filled buckets being raised to the top and turning again toward the bottom, discharge of themselves what they have brought into the reservoir.”
Fig. 77.
The Persian Wheel. Two prominent defects exist in the noria. First, part of the water escapes after being raised nearly to the required elevation. Second, a large portion is raised higher than the reservoir placed to receive it, into which it is discharged after the vessels begin to descend; to obviate this the Persian wheel was devised.
The vessels in which the water is raised, instead of being fastened to the rim, or forming part of it, as in the preceding figures, are suspended from pins, on which they turn, and thereby retain a vertical position through their entire ascent; and when at the top are inverted by their lower part coming in contact with a pin or roller attached to the edge of the gutter or reservoir, as represented in the figure. By this arrangement no water escapes in rising, nor is it elevated any higher than the edge of the reservoir; hence, the defects in the noria are avoided. It is believed, to have been used in Europe ever since the time of the Romans.