PARABOLIC PYRAMIDOID, is a solid figure, thus named by Dr Wallis from its genesis or formation, which is thus: Let all the squares of the ordinates of a parabola be conceived to be so placed, that the axis shall pass perpendicularly through all their centres; then the aggregate of all these planes will form the parabolic pyramidoid. This figure is equal to half its circumscribed parallelopipedon. And therefore the solid content is found by multiplying the base by the altitude, and taking half the product; or the one of these by half the other.