4 A Cone is that which is comprehended of a conicall and a base.
Here the base is a circle.
Therefore
5 It is made by the turning about of a right angled triangle, the one shanke standing still.
As it appeareth out of the definition of a variable body.
And
6 A Cone is rightangled, if the shanke standing still be equall to that turned about: It is Obtusangeld, if it be lesse: and acutangled, if it be greater. ê 18 d xj.
