The figure inscribed as above in a sphere is equal [in volume ] to a cone whose base is a circle equal to the surface of the figure inscribed in the sphere and whose height is equal to the perpendicular drawn from the canter of the sphere to one side of the polygon.

Subtracting the two Rohomba OCC'T from OBB'T
from each other we get two blue traingle which is
equal to revlution of OBC arround AA'.