**FRUSTUM** (Latin for a "piece broken off"), a term in geometry for the part of a solid figure, such as a cone or pyramid, cut off by a plane parallel to the base, or lying between two parallel planes; and hence in architecture a name given to the drum of a column.

19 the blast orifice B is set much lower, and the steam is discharged through a **frustum** of a cone set in the upper part of the smoke-box into the short chimney.

Hence the area of an ellipse whose axes are 2a and 2b is Trab; and the volume of an ellipsoid whose axes are 2a, 2b and 2c is t rabc. The area of a strip of an ellipse between two lines parallel to an axis, or the volume of the portion (**frustum**) of an ellipsoid between two planes parallel to a principal section, may be found in the same way.

The volume of a **frustum** of a cone, for instance, can be expressed in terms of certain magnitudes by a certain formula; but not only will there be some error in the measurement of these magnitudes, but there is not any material figure which is an exact cone.

This pulley has fixed to one side, and concentric with it, a short **frustum** of a hollow cone.

This **frustum** is made always to turn along with the shaft by being fitted on a square portion of it, or by means of a rib and groove, or otherwise, but is capable of a slight longitudinal motion, so as to be pressed into, or withdrawn from, the hollow cone by means of a lever.

At a small distance from the pulley the shaft carries a short **frustum** of a solid cone accurately turned to fit the hollow cone.