Magic is a term used to signify an unlawful and wicked kind of science, depending, as was pretended, on the assistance of superhuman beings and of departed souls. The term was anciently applied to all kinds of learning, 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 found in immense quantities in the limestone caves in the south-western States. [Footnote 11: See Potash, Chapter VII., article Glass.] What do you mean by _Marly_?