Therefore
14 The sides of an Icosaedrum are 30. plaine angles 60. the solid 12.
And
15 If twentie ordinate and equall triangles be joyned with solid angles, they shall comprehend an Icosaedrum.
This fabricke is ready end easie, as is to be seene in this example following.
16. If ordinate figures, to wit, a double quinquangle, and one decangle be so inscribed into the same circle, that the side of both the quinquangle doe subtend two sides of the decangle, sixe right lines perpendicular to the circle and equall to his ray, five from the angles of one of the quinquangles, knit together both betweene themselves, and with the angles of the other quinquangle; the sixth from the center on each side continued with the side of the decangle, and knit therewith the five perpendiculars, here with the angles of the second quinquangle, they shall comprehend an icosaedrum. è 15 p xiij.
For there shall be made 20 triangles, both equilaters and equall. Let there be therefore two ordinate quinquangles, the first aeiou; The second ysrlm; each of whose sides let them subtend two sides of a decangle; to wit, utym, let it subtend ya, and am. Then let there be five perpendiculars from the angles of the second quinquangle yj, sy, rv,