372 



BOOK IX. 



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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 



OF THE AXLE. 



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 ; their 

 length, excluding the tenons, being two feet and three digits. One end of the 

 spoke is mortised into the axle, where it is firmly fastened with pegs ; the 

 wide part of the other end, in the shape of a triangle, is mortised into the 

 outer segment opposite it, keeping the shape of the same as far as the segment 

 ascends. They also are joined together with wooden pegs glued in, and these 

 pegs are driven into the spokes under the inner disc. The parts of the spokes 

 in the shape of the triangle are on the inside ; the outer part is simple. This 

 triangle has two sides equal, the erect ones as is evident, which are a palm 

 long ; the lower side is not of the same length, but is five digits long, and a 

 mortise of the same shape is cut out of the segments. The wheel has sixty 

 teeth, since it is necessary that the rundle drum should revolve twice while 

 the toothed wheel revolves once. The teeth are a foot long, and project one 

 palm from the inner disc of the wheel, and three digits from the outer disc ; 



