As here, aei, and ouy, and srl, are sections.
10. A section is made up by finding of the center.
The Invention of the center was manifest at the [7 e xv]: And so here thou seest a way to make up a Circle, by the [8 e xv].
11 The periphery of a section is divided into two equall parts by a perpendicular dividing the base into two equall parts. 20. p iij.
Let the periphery of the section aoe, to be halfed or cut into two equall parts. Let the base ae, be cut into two equall parts by the pendicular io, which shall cut the periphery in o, I say, that ao, and oe, are bisegments. For draw two right lines ao, and oe, and thou shalt have two triangles aio, and eio, equilaters by the [2 e vij]. Therefore the bases ao, and oe, are
equall: And by the [32. e xv]. equall peripheries to the subtenses.
Here Euclide doth by congruency comprehende two peripheries in one, and so doe we comprehend them.