372

BOOK IX.

A—Axle. B —Water-wheel. C—Drum composed of rundles. D—Other axle.E —Toothed wheel. F —Its spokes. G —Its segments. H—Its teeth. I—Cams

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segment, measured over its round back, is four feet and three palms long.There are four spokes, each two palms wide and a palm and a digit thick; theirlength, excluding the tenons, being two feet and three digits. One end of thespoke is mortised into the axle, where it is firmly fastened with pegs ; thewide part of the other end, in the shape of a triangle, is mortised into theouter segment opposite it, keeping the shape of the same as far as the segmentascends. They also are joined together with wooden pegs glued in, and thesepegs are driven into the spokes under the inner disc. The parts of the spokesin the shape of the triangle are on the inside ; the outer part is simple. Thistriangle has two sides equal, the erect ones as is evident, which are a palmlong ; the lower side is not of the same length, but is five digits long, and amortise of the same shape is cut out of the segments. The wheel has sixtyteeth, since it is necessary that the rundle drum should revolve twice whilethe toothed wheel revolves once. The teeth are a foot long, and project onepalm from the inner disc of the wheel, and three digits from the outer disc;