is a solid generated by the rotation of a parabola about its axis. This solid is equal to half its circumscribed cylinder; and therefore if the base be multiplied by the height, half the product will be the solid content.

**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.

**Parabolic Space**, is the space or area included by the curve line and base or double ordinate of the parabola.

**Parabolic Spindle**, is a solid figure conceived to be formed by the rotation of a parabola about its base or double ordinate.

**Parabolic Spiral**, is a curve arising from the supposition that the common or Apollonian parabola is bent or twisted till the axis come into the periphery of a circle, the ordinates still retaining their places and perpendicular positions with respect to the circle, all these lines still remaining in the same place. This figure is sometimes called the Helicoid parabola.