and 12, the heighth is 216. This added to the triangular base, 15.18/31. or 15.3/5, almost twise taken, that is, 31.1/5, doth make 247.1/5, for the summe of the whole surface. But the plaine of the same base 15.3/5, and the heighth 12. is 187.1/5, for the whole solidity.
So in the pentaedrum, the second prisma, which is called Cuneus, (a wedge) of the sharpnesse, and which also more properly of cutting is called a prisma, the whole surface is 150, and the solidity 90.
13 A prisma compounded of pentaedra's, is either an Hexaedrum or Polyedrum: And the Hexaedrum is either a Parallelepipedum or a Trapezium.
14 A parallelepipedum is that whose opposite plaines are parallelogrammes ê 24. p xj.
Therefore a Parallelepipedum in solids, answereth to a Parallelogramme in plaines. For here the opposite Hedræ or flattes are parallell: There the opposite sides are parallell.
Therefore
15 It is cut into two halfes with a plaine by the diagonies of the opposite sides. 28 p xj. It answereth to the 34. p j.
Let the Prisma be of sixe bases ai, yo, ye, ui, si, au. The diagonies doe cut into halfes, by the [10. e x]. the opposite bases: And the other opposite bases or the two prisma's cut, are equall by the [3 e]. Wherefore two prisma's are comprehended of bases, equall both in multitude and magnitude: therfore they are equall.