The fifteenth Booke of Geometry, Of the Lines in a Circle.
As yet we have had the Geometry of rectilineals: The Geometry of Curvilineals, of which the Circle is the chiefe, doth follow.
1. A Circle is a round plaine. è 15 d j.
As here thou seest. A Rectilineall plaine was at the [3 e vj], defined to be a plaine comprehended of right lines. And so also might a circle have beene defined to be a plaine comprehended of a periphery or bought-line, but this is better.
The meanes to describe a Circle, is the same, which was to make a Periphery: But with some difference: For there was considered no more but the motion, the point in the end of the ray describing the periphery: Here is considered the motion of the whole ray, making the whole plot conteined within the periphery.
A Circle of all plaines is the most ordinate figure, as was before taught at the [10 e iiij].
2 Circles are as the quadrates or squares made of their diameters 2 p. xij.
