11 A Pyramis is a plaine solid from a rectilineall base equally decreasing.
As here thou conceivest from the triangular base aei, unto the toppe o, the triangles aoe, aoi, and eoi, to be
In the pyramis aeiou, thou seest from the quadrangular base aeio, unto the toppe u, foure triangles in like manner to be raised.
Therefore
12 The sides of a pyramis are one more than are the base.
The sides are here named Hedræ.
And