_Oscillation_, a swinging backward and forward.

_Gravity_, the tendency of a body toward the centre of the earth.

_Registering_, recording.

[Ill.u.s.tration: CHARCOAL BURNING.]

[Ill.u.s.tration: GOLD MINERS WASHING ORE.]

To whom is the invention of Gunpowder ascribed?

Most authors suppose it was invented by Bartholdus Schwartz, a monk of Goslar, a town of Brunswick, in Germany, about the year 1320; it appears, however, that it was known much earlier in many parts of the world, and that the famous Roger Bacon, who died in 1292, knew its properties; but it is not certain that he was acquainted with its application to fire-arms.

Who was Roger Bacon?

A learned Franciscan, born at Ilchester, England, in 1214. He studied at Oxford, and afterwards became professor at that great University.

He was familiar with every branch of human knowledge, but was especially distinguished for his extraordinary proficiency in the natural sciences. To him we owe the invention of the telescope; that of gunpowder is ascribed to him, as stated above, although we have no evidence to show whether he discovered its ingredients himself, or whether he derived the knowledge from some ancient ma.n.u.scripts. Bacon suffered some from the ignorance of the age in which he lived, many of his experiments being looked upon as magic. He died at Oxford in the year 1294.

What is understood by Magic?

Magic is a term used to signify an unlawful and wicked kind of science, depending, as was pretended, on the a.s.sistance 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 pa.s.sive 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 pa.s.sages 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 pota.s.sa.[11] It is found in earthy substances; sometimes native or pure, in the form of a shapeless salt. Vast quant.i.ties 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 quant.i.ties in the limestone caves in the south-western States.

[Footnote 11: See Potash, Chapter VII., article Gla.s.s.]

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 gla.s.ses, or by reflection. The invention of the telescope is one of the n.o.blest 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.

Who was Galileo?

A most eminent astronomer and mathematician, born at Florence, in Italy. His inventions and discoveries in Astronomy, Geometry, and Mechanics, contributed much to the advancement of those sciences. He died in 1642.

_Astronomer_, one versed in Astronomy.

_Mathematician_, one versed in Mathematics; a science which treats of magnitude and number.

What is Astronomy?[12]

That science which teaches the knowledge of the heavenly bodies, with the nature and causes of their various phenomena.

[Footnote 12: See Chapter xviii.]

What is Geometry?

An ancient, perfect, and beautiful science, which treats of the relations and properties of lines, surfaces, and solids.

What is meant by Mechanics?

The science which investigates the laws of forces and powers, and their action on bodies, either directly or by machinery. When the term _mechanic_ is applied to a _person_, it means one skilled in mechanics, accustomed to manual labor.

_Investigate_, to search, to inquire into.

_Manual_, performed by the hand.