7. The angles in the center or periphery of equall circles, are as the Peripheries are upon which they doe insist: And contrariwise. è 33 p vj, and 26, 27 p iij.
Here is a double proportion with the periphery underneath, of the angles in the center: And of angles in the periphery. But it shall suffice to declare it in the angles in the center.
First therefore let the Angles in the center aei, and ouy be equall: The bases ai, and oy, shall be equall, by the [11 e vij]: And the peripheries, ai, and oy, by the [32 e xv], shall likewise be equall. Therefore if the angles be unequall, the peripheries likewise shall be unequall.
The same shall also be true of the Angles in the Periphery. The Converse in like manner is true: From whence followeth this consectary:
Therefore
8. As the sectour is unto the sectour, so is the angle unto the angle: And Contrariwise.
And thus much of the Sectour.
9. A section is a segment of a circle within cōprehended of one right line, which is termed the base of the section.