earning, and in particular to the science of the Magi or
Wise Men of Persia, from whom it was called magic. _Natural_ magic is
no more than the application of natural active causes to passive
things or subjects, to produce effects apparently supernatural.

_Supernatural_, beyond the powers of nature; miraculous.

Of what is Gunpowder composed?

Of saltpetre,[10] sulphur, and charcoal, mixed together and powdered;
its explosive force when fired, is owing to the instantaneous and
abundant liberation of gaseous matter by the intense heat resulting
from the action of the combustibles upon the saltpetre. It is not
known by whom it was first applied to the purposes of war, but it is
certain that it was used early in the fourteenth century. Cannons were
used at the battle of Cressy, in 1346; small guns, or muskets, were
introduced into the Spanish army in 1521.

[Footnote 10: See Chapter XIII.]

_Explosive_, bursting out with violence and noise.

_Liberation_, a setting at liberty.

Is not Gunpowder highly combustible?

So combustible is gunpowder, that a single spark of fire, lighting
upon any of it, will cause it to explode with immense force; and
instances have occurred, when any store or magazine of it has taken
fire, that have been attended with the most fatal effects. It is
useful to the miner and engineer as a ready means of overcoming the
obstacles which are presented in their search for mineral treasures,
and in procuring materials for building. From many passages in the
ancient authors, there is reason to suppose that gunpowder, or a
composition extremely like it, was known to them; but it does not
appear to have been in general use, and the invention of fire-arms is
comparatively modern. Dynamite, a recent invention, has a still
greater explosive force than gunpowder.

_Engineer_, one who works or directs an engine.

_Obstacles_, hinderances, obstructions.

What is Saltpetre?

A bitter kind of salt, called by the ancients nitre, but more commonly
among us saltpetre. It is composed of nitric acid and potassa.[11] It
is found in earthy substances; sometimes native or pure, in the form
of a shapeless salt. Vast quantities are found in several of the
marly earths of the East Indies, China, Persia, and also in South
America. In India it is found naturally crystallized, and forming thin
crusts upon the surface of the earth. It is especially abundant in the
United States, being