138 



BOOK V. 



waxed margin through the first semi-circular line, and reaching to the second, 

 there proceed straight lines converging toward the centre of the hemicycle ; 

 these mark the middles of intervening spaces lying between other straight lines 

 which extend to the fourth semi-circular line. But all lines whatsoever, from 

 the waxed margin up to the fourth line, whether they go beyond it or not, 

 correspond with the graduated lines which mark the minor spaces of a rod. 

 Those which go beyond the fourth line correspond with the lines marking 



A WAXED SEMICIRCLE OF THE HEMICYCLE. B SEMICIRCULAR LINES. C STRAIGHT 



LINES. D LINE MEASURING THE HALF. E LlNE MEASURING THE WHOLE. F TONGUE. 



