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.” [Illustration: 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. [Illustration: FIG. 78.] GAINING AND LOSING BUCKETS. In the latter part of the Sixteenth, or beginning of the Seventeenth Century a machine which is entitled to particular notice on account of its being, as claimed, the first one of the kind to be _self-acting_, for raising water was in use in Italy. It is ascribed to Gironimo Finugio who put one in operation at Rome in 1616. [Illustration]