lasts but a quarter of an hour.

A _fire ball_ consists of an open work sack internally strengthened with a
sheet iron shell, and fitted with the Lamarre white composition. After the
charging has been done, the sphere is wound with string, which is made to
adhere by means of tar, and canvas is then wrapped around the whole.
Projectiles of this kind, which have diameters of 6, 8, 11, and 13 inches,
are shot from mortars.

The _illuminating grenade_ (Fig. 13) consists of a sphere of vulcanized
rubber, two inches in diameter, charged with the Lamarre white composition.
The sphere contains an aperture to allow of the insertion of a fuse. The
priming is effected by means of a tin tube filled with a composition
consisting of three parts of priming powder, two of sulphur, and one of
saltpeter. These grenades are thrown either by hand or with a sling, and
they may likewise be shot from mortars. Each of these projectiles
illuminates a circle thirty feet in diameter for a space of time that
varies, according to the wind, from sixty to eighty seconds.

The _percussion signal_ (Fig. 14) consists of a cylinder of zinc, one inch
in diameter and one and a quarter inch in length, filled with Lamarre red
composition. It is provided with a wooden handle, and the fuse consists of
a capsule which is exploded by striking it against some rough object. This
signal burns for nearly a minute.

_Belgian illuminating balls and cylinders_ are canvas bags filled with
certain compositions. The cylinders, five inches in diameter and seven in
length, are charged with a mixture of six parts of sulphur, two of priming
powder, one of antimony, and two of beeswax cut up into thin slices. They
are primed with a quickmatch. The balls, one and a half inch in diameter,