It was at first supposed that the expansion of the metal would be so great, when heated to a red or white heat, as to prevent the ball from entering the piece; it is found, however, that the windage is still sufficient for loading with facility.

These red-hot balls are principally used to fire wooden buildings, ships, and other combustible matter.

They are therefore much used as a projectile for coast defence, and all fortifications on the seaboard should be provided with furnaces and grates, arranged so as to heat them with facility and rapidity.
[Footnote 35: In Mexico, where iron is scarce, copper is used for shot and shells; but it is a poor substitute.] There are several kinds of _hollow-shot_ and _shells_, called _bombs, howitzes, grenades_, &c.

They are made of cast iron, and usually in a spherical shape, the cavity being concentric with the exterior surface.
The cavity was formerly made eccentric with the exterior, under the belief that the heavier side would always strike first.

The rotary motion of the shell during its flight rendered this precaution of no use.