صور الصفحة
النشر الإلكتروني

NATURAL HISTORY.—MINERALS. Acid, (acidus, L.) Lit. a substance with | Equilateral, (æquus, latus, L.) equala sour, pungent taste.*

sided. Amorphous, Ta, morphe, G.) without Graphite, (grapho, G.) definite or regular shape.

Mineralogy, (logos, G.) Base, (basis, G.) Lit. the foundation : | Nitrogen, (nitron, gennao, G.) Lit. pro

the leading ingredient. Hence basic. ducer or generator of nitre. Botany, (botane, G.)*

Octahedron, (octo, hedra, G.) Carbon. (carbo, L.) Lence carbonic acid Organ, (organon, G.) Hence organic.

and carbonate (a salt containing car inorganic, organized, organization, bonic acid).

organism. Crystal, (crystallos, G.) Hence crystal Oxygen, (oxys, gennao, G.) Lit. prolize and crystallization.

ducer or generator of acids. Cube, (cubos, G.) .

Parallelogram, (para, allēlon, gram

ma, G.) a four-sided figure, whose

opposite sides are parallel, i.e., ex* When the ordinary meaning of altend in the same direction.' word is sufficiently explained in the

Prism, (prisma, G.

Silica, (silex, L.) Lit. the earth of flints. text of the lessons, the explanation is

Hence silicon or silicium, silicious. not repeated in the Vocabularies. | Zoology, (zoon, logos. G.)

OBJECTS AND DIVISIONS OF NATURAL HISTORY. If we look around us, we shall find that our world, the habitation which God has given us, is full of the most beautiful and interesting objects. Animals, in countless thousands, roam over the earth, soar into its atmosphere, or disport themselves in its waters. It produces an immense number of plants, which contribute alike to its comfort and elegance as the abode of man: Nor are the materials, of which the earth itself is composed, less worthy of our attention. Human skill and labour have penetrated far beneath its surface, and thence, from stores that seem to be in. exhaustible, have extracted much that is useful, and much also that is wonderful.

Surely it is right and becoming that we should have some intelligent acquaintance with what is thus presented to our notice. We can, indeed, scarcely help inquiring into the nature of those things which interest us, just as the child wishes to know the construction of his plaything, and will even tear it to pieces to gratify his curiosity. But it is not curiosity alone which prompts our inquiries into the objects and processes of nature. Such inquiries are profitable as well as pleasing; they give us the means of increasing our comforts, and of alleviating our ills; they expand and elevate

our minds, and lead us to the contemplation of that Great Being by whom all things exist.

That we may not be bewildered by the endless variety of nature's productions, it is necessary to arrange them into groups or classes, according to their several properties. Each group is then subdivided into several smaller ones, and these are again subdivided as often as may be necessary. In this way we obtain a system of classification, to which each individual object, whether animate or inanimate, may be referred, and its place correctly ascertained.

To classify thus all the objects which exist in nature, and to describe their appearance, structure, properties, and uses, is the business of NATURAL History,

Some bodies are made up of parts different from each other, which serve as instruments for performing certain processes or functions serviceable to the whole body. For example, a man has eyes for seeing, lungs for breathing, and feet for walking. In the same manner a tree has roots, branches, leaves, &c., all performing their appropriate functions. Such parts are called organs, and those bodies that possess them are said to be organized. Organized bodies are of two kinds:-Animals, which are endowed with the powers of sensation and voluntary motion; and Vegetables, or Plants, which are destitute of those powers. Plants, as well as animals, may be regarded as, in one sense, living creatures.

It will easily be perceived that stones, metals, earths, &c., have no organs; they are therefore said to be inorganic. Inorganic bodies are also called Minerals, because many of the most important of them are dug out of mines.

Thus the science of Natural History falls into three great divisions, corresponding to the three great classes, or (as they are usually termed) kingdoms, in which the objects of pature may be arranged. They are:

I. Mineralogy, which treats of the Mineral Kingdom ;
II. Botany, which treats of the Vegetable Kingdom ;
III. Zoology, which treats of the Animal Kingdom.

FORM AND STRUCTURE OF MINERALS. It has been said that minerals are distinguished both from plants and animals by being destitute of organization. They therefore undergo none of those processes which organs are intended to carry on. A stone does not grow; if it increases in size, it can only be by the addition or aggregation, from without, of matter similar to that of which it is composed. But plants and animals grow from within, by adopting new matter into their organic system, and thereby developing their own parts and members. Again, there appears to be no definite or necessary limit to the time during which a stone may continue to exist. Organized bodies, on the other hand, after giving birth to others of the same species, gradually decay and die.

Nearly all mineral substances are solid. Mercury, however, one of the metals, is usually in a fluid state, though it can be solidified, or frozen, by exposure to intense cold. Water itself is sometimes reckoned a mineral substance.

Some minerals consist of minute particles simply collected together, with no regularity of structure, or constancy of external form. These are said to be amorphous. But by far the greater number seem to have their particles arranged according to some definite law, and are found to assume, under favourable circumstances, more or less regular geometrical forms, bounded, for the most part, by plane surfaces and straight lines. Such forms are called crystals, and the substances composing them are said to be crystallized. The word crystal originally included the idea of clearness or transparency; but, in speaking of minerals, that notion must be at once dismissed. It is applied to a solid body, whether transparent or opaque, which exhibits naturally (that is, without being cut or moulded in any way by man's instrumentality) a certain regularity of shape. Among the simpler forms of crystallization are the cube (fig. 1), a well-known solid, of which we have an example in dice; the octahedron (fig. 2), with cight faces, each of which is an equilateral triangle; and the prism (figs. 3 and 4), which

FIG. 2.

has two equal and similar ends, and whose other faces are parallelograms. Other forms are almost innumerable, and some of them are extremely Fig. 1. complex. Sugar-candy, though it does not belong to the mineral kingdom, may be mentioned as a familiar example of a crystallized substance. In loaf-sugar, the crystallization is less obvious, but still distinctly visible.

Many substances can be crystallized by artificial means; as, for example, by allowing them to cool slowly after being Fig. 3. Fig. 4. melted, or by dissolving them in water, and leaving the solution gradually to evaporate. But we are ignorant, as yet, of the means by which the majority of crystals belonging to the mineral kingdom are produced. Natural crystals of quartz have been found of an immense size; one in the Museum at Paris measures no less than three feet in diameter. Carbonate of lime crystallizes in an incredible variety of forms. But the most beautiful of known crystals is the diamond; it consists of pure carbon, the same substance which appears, in its amorphous state, as lampblack, soot, or charcoal, and is then by no means remarkable for its beauty.

How wonderful the facts thus brought before us! Whence, we may well ask, this order and regularity? Whence did the lifeless particles of matter derive the property of arranging themselves in mathematical forms? Have we not here a striking illustration of the strange yet true remark, that the Creator, in constructing and regulating the material universe, “works by geometry.”

COMPOSITION OF MINERALS. THOSE substances which men of science have not been able to decompose, are in the meantime regarded as simple or elementary. Their number is about sixty; but it is probable that some of these may hereafter be shown to be compound. All of them occur in the mineral kingdom, either separately or in combination; but not more than twenty are common, and only about twelve abundant. Carbon, sulphur, and a few of the metals, are found pure; the first in two distinct and very dissimilar forms—diamond, and graphite or plumbago, of which pencils are made. Oxygen and nitrogen are mixed together, but not combined, in atmospheric air. The rest are always combined with these, or with one another.

Simple substances usually unite in pairs, and by their union form compounds, whose qualities are often very different from those of either element. The new substance thus produced may again unite, either with a third element, or with another compound. Again, the same substances may be combined in several different proportions, and form a series of compounds with little or no resemblance to each other. Thus it is that the objects of nature, though the number of their elementary ingredients is comparatively small, assume that wondrous variety of character and appearance, by which they are so well fitted to charm the eye, as well as to promote the comfort and convenience of man.

The most extensively diffused of all the recognised elements is oxygen, a gaseous substance, without colour, smell, or taste. Besides being essential to the existence of all organized bodies, it is a principal ingredient of the atmosphere and the ocean, and enters into the composition of the more abundant minerals. The sand of the desert, and the soil of the cultivated field, alike owe some of their qualities to its presence; it is found in the rugged granite and the finest marble, in the shapeless clay and the glowing sapphire; it feeds the flames in our grates, and glitters in the frozen glaciers; without it, every plant would droop, and every

« السابقةمتابعة »