Proposition 26
 

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.
 
BOC is the tringle which is revolved arround AA'and is equal in volume to the difference between rhombi OCTC' and OBTB'which is a cone whose base is equal to the urface of the frustum BB'C'C and whose height is p.