all these are alike chemical phenomena.
When an explosion takes place, the solid
materials, or some of them, are instantly
converted into gases; and these gases occupy
so much more space than the solids, that they
must displace air to obtain room for
themselves, and the violence of this displacement
occasions the noise of the explosion. If the
materials be confined within a strong paper
case, or a gun barrel, the greater effort of
the expanding gases to rend it increases the
intensity of the noise. If flame be required,
exploding materials must be loosely confined,
and the solids must be such that their
resultant gases will inflame or ignite. If
sparks be wanted, some one of the materials
must bear an intense heat and reflect an
intense light before being dissipated. All
these are chemical effects; and different
combinations of ingredients are necessary to
ensure their production. For simple explosion
without other attendant phenomena,
gunpowder is the chief or only agent; for a
recoil motion, such as that of rockets and
serpents, a little less proportion of nitre is
used; for flame, charcoal is as much as
possible excluded; for sparks, charcoal
preponderates, aided by metal filings. The slow
or the quick burning of substance, the
production of sound or of light, the exhibition of
flames or of sparks—are all the result of
chemical laws.

No one can dispute the optical beauty of
fire-works. The sparks and the flames may
be regarded as luminous particles, rendered
visible by intense heat; but the most
gorgeous effects are produced by the reflection
of coloured rays derived from various
chemical mixtures; the nitre and the sulphur
and the charcoal, one or more, produce
the flame and the sparks, but it is
something else which imparts, brilliancy of colour.
The theatres are famous show places for
these coloured fires. When Jessonda is about
to be immolated, and the Portuguese besiege
the castle, one feels terribly hot at the idea of
the approaching flames; and when Don
Juan is pushed down by small devils in
horns, tails, and brown tights through a
trap-door, there are misgivings as to the
nature of the red fire into which he is
plunged. But there is nothing to fear.
Nitrate of strontian does it all; and chemistry
thus comes to the aid of Spohr and Mozart.
Very white light, used for "white speckles"
or illumination lights in ornamental
fireworks, owe much of their whiteness to zinc
filings. Pale blue light is indebted to a little
antimony as well as zinc. Red is produced
by the addition either of mica or nitrate of
strontian to the other ingredients. Purple
fire is aided by red lead; yellow by black-
lead; green by nitrate of copper; yellowish-
white by red orpiment, and so on. The
chemistry of colour is taxed by the pyrotechnist
to the utmost: a new colour would be
welcomed by him as much as a new sauce by
an epicure or a new idea by a poet. Nor
are radiant and reflected coloured lights alone
treasures to him; but he occasionally makes
use of transmitted light. In the old-fashioned
illuminating lamps, fed with oil instead of
gas, the gay colours are due to the little
glass vessels and not to the flame itself;
they are examples of coloured light produced
by transmission. This transmitted light does
wonders on the stage. When Mario and
Grisi in La Favorita mope in the moonlight;
or when the dead nuns in Robert le Diable
dance an unearthly ballet, we may make a
tolerably near guess that a green glass bottle,
placed in front of a strong light, produces the
moonshine.

The laws of dynamics or mechanical
movement are, besides those of chemistry,
illustrated and brought into play in pyrotechnics.
The ascent of a sky-rocket, and the revolving
of a fire-wheel, are beautiful examples of these
laws. When a cannon is fired, the ball goes one
way and the cannon another—the latter being
affected by a recoil. It is true this recoil is
very slight, on account of the great weight of
the cannon, and the mode in which it is
connected with the ground. The gunpowder
behind the ball explodes or expands into gas;
this gas must and will find room for itself,
either by driving the ball out of the cannon,
or by driving the cannon away from the
ball, or both. Apply this to a sky-rocket,
A rocket is a strong paper tube, filled with
inflammable matter. It is fixed vertically
to a stick; and, when fired at the lower end,
the composition becomes converted into a
gas. This gas, pressing and driving in all
directions, finds an outlet, rushing out with
great force; and is accompanied by a brilliant
shower of sparks at the opened lower end;
but it also drives the case itself upwards by
the recoil. The ascent of the rocket is wholly
due to the efforts of the gaseous exploded
mixture to escape. This recoil is the same
in principle as that displayed by a screw-
propeller, however different it may appear in
action. The screw must turn round, because
a steam-engine irresistibly compels it, but it
cannot do this without either driving the
water in one direction or the ship in another.
It does both; the ship recoils under the force
used, and thus is it moved along. The
beautiful revolving wheels which form such
attractive objects in pyrotechnic displays are
in like manner dependent on the dynamic
action of the wheel. They are kindled at
certain points—sometimes at the periphery,
sometimes at the side of the spokes—and the
expanding gases rush out at the orifices. But
this rush tends to recoil against the wheel
itself; and, if the orifice be judiciously placed
the recoil will cause the wheel to rotate with
great velocity. There are many machines in
which a rotatory movement is given by the
escape of water or air through orifices, on a
principle somewhat analogous. The modes
of applying these chemical, and optical, and