[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?

Consisting of marl, a kind of earth composed of different proportions of clay and carbonate of lime; it is much used for manure.  There are several different-colored marls, each possessing different qualities.  The most common are the red and the white, though there are grey, brown, blue, and yellow colored marls.

What is a Telescope?

An optical instrument, which serves for discovering and viewing distant objects, either directly by glasses, or by reflection.  The invention of the telescope is one of the noblest and most useful of which modern ages can boast, since by means of this instrument the wonderful motions of the planets and fixed stars, and all the heavenly bodies, are revealed to us.  The honor of the invention is much disputed; it is certain, however, that the celebrated Galileo was the first who improved the telescope so as to answer astronomical purposes.  The name is formed from two Greek words, one signifying far, the other to observe.

     Optical, relating to Optics, the science of vision.

     Astronomical, relating to Astronomy.