‹‹‹ Vitr. 3.5.5 | Table of Contents | Vitr. 3.5.7 ›››
6Within the line dropt from the angle of the abacus, at the distance of one and a half of the parts last found, let fall another vertical line, and so divide it that four parts and a half being left under the abacus, the point which divides them from the remaining three and a half, may be the centre of the eye of the volute; from which, with a radius equal to one half of one of the parts, if a circle be described, it will be the size of the eye of the volute. Through its centre let an horizontal line be drawn, and beginning from the upper part of the vertical diameter of the eye as a centre, let a quadrant be described whose upper part shall touch the under side of the abacus; then changing the centre, with a radius less than the last by half the width of the diameter of the eye, proceed with other quadrants, so that the last will fall into the eye itself, which happen in the vertical line, at a point perpendicularly under that of setting out.
6Then let another line be drawn, beginning at a point situated at a distance of one and a half parts toward the inside from the line previously let fall down along the edge of the abacus. Next, let these lines be divided in such a way as to leave four and a half parts under the abacus; then, at the point which forms the division between the four and a half parts and the remaining three and a half, fix the centre of the eye, and from that centre describe a circle with a diameter equal to one of the eight parts. This will be the size of the eye, and in it draw a diameter on the line of the “cathetus.” Then, in describing the quadrants, let the size of each be successively less, by half the diameter of the eye, than that which begins under the abacus, and proceed from the eye until that same quadrant under the abacus is reached.