In the science of material things, mechanics takes account of forces that act on masses from without; physics, of those that act from within, or which, in some way, modify the condition of the bodies themselves. Both branches were, till recently, included in the vaguely comprehensive term “Natural Philosophy,” and the partial separation observed in modern treatises and text-books gives a little more distinctness to the facts presented. Under the former the earth is contemplated as a planet, obedient to the universal law of gravitation, and moving regularly in its orbit. The mechanism of the system is complete; the measure and adjustment of all the parts perfect.

GEOLOGY,

As a physical science, considers the earth apart from the solar system with which it is connected, and takes account of its materials and structure, and the forces that unite them. Its position in the group is about midway between mechanics and chemistry, being closely allied to other natural sciences, while its phenomena are occasionally varied by both mechanical and chemical agents.

PHYSIOGRAPHIC GEOLOGY

Treats of the earth’s exterior physical features; of its form—an oblate spheroid—of its surface, oceans, continents, seas, lakes and rivers, hills, mountains, valleys and plains; of soils made from previously existing organic or inorganic substances, the detritus of rocks containing various minerals and small particles of decomposed vegetable matter. The materials of this outer covering of the earth are from many different sources, and variously constituted. From the finest grains of sand, clay, and loam, to pebbles, boulders, and fragments of enormous dimensions, they are mingled apparently without any fixed order or proportions; sometimes but slightly covering the solid rock, at others piling it up in ridges and hills of considerable height. In this surface formation are included ancient sea-beaches, lake and river terraces, deltas, deposits of sand and clay, with vast beds of marls, peat and calcareous tufa,[1] all the progressive accumulations since the present order of things began. In some of these deposits, more recent than the Drift[2] period, fossils are abundant and very full of interest. In New Zealand the bones of a bird[3] were found which exceed in bulk those of the largest horse, and are now in the museum of the College of Surgeons, London. The bird when alive was eleven or twelve feet high.

Less than a century ago what might have been a fossil elephant was found imbedded in ice on the coast of Siberia, and in such a perfect state of preservation that the people fed their dogs on its flesh. The animal was well covered with hair, and adapted to a cool climate, a representative of an extinct race. How it was imbedded, or how long it had been preserved in that condition, no one knows.

In Great Britain are found fossils of the rhinoceros and hippopotamus, of elephants, tigers, hyenas and giant elks, all of which are extinct species. The United States is especially prolific in the remains of huge mammals. The mastodon and megatherium were doubtless indigenous to this country. The latter had a thigh bone three times as large as the largest elephant, and the cavity through which it passed, indicates a spinal cord an inch in diameter. These largest skeletons were found in Georgia and South Carolina. Those of the mastodon are numerous, and found in many different places. Physiographic geology is a study intensely interesting, and of great practical importance, as it bears directly on many of the industries of life; but this general notice is sufficient.

LITHOGRAPHIC GEOLOGY.

The ultimate particles of material bodies, of which we know but little, exert such force or influence on each other as to decide the character of the mass; even if the atoms are identically the same in substance they may come together in a way to secure different results. The bulk of the solid part of the earth is rock, but all rock is not the same. We find several species of granite, of limestone, and sandstone, a long list. But the whole may be divided into two classes, stratified and unstratified. Whatever the two classes seem to have in common, they are not of the same origin. The first occur in layers or strata, others are crystalline and massive. The loose materials, such as sand, clay and gravel, that have accumulated at the bottom of the pond or lake, are found arranged in beds or parallel layers. The streams carry the materials from the highlands, and they are at length deposited in the basin, and when hardened become stratified rocks. As this process is still going on, and recently formed strata are found approaching the consistency of stone, it is but reasonable to conclude that all rocks of this class, being formed in like manner under the water, are of aqueous origin. They are further classed according to certain peculiarities, either of material or formation.

Gneiss, abundant in all parts of New England, is a kind of stratified granite, of about the same materials, but splits readily into slabs that are used both for building purposes and flagging stones.

Mica slate resembles gneiss, has the same minerals, but more mica, and is of a more slaty structure, and the glistening particles of mica abound in it.

There are several other kinds of slate, named from the minerals that predominate in them, or the purposes for which they are mostly used. Roofing slate of excellent quality is extensively quarried in Maine, Vermont and Massachusetts.

Quartz rock consists mainly of quartz, but often has more or less mica. Sandstone is of kindred formation, the principal part of which is quartz, reduced to sand, and the grains more or less firmly united. In both the colors are various.

Conglomerate consists of water-worn pebbles of various kinds and sizes cemented together, and sometimes making a strong, compact rock.

The limestone formations are extensive in nearly all countries. In their structure some are very compact and break with a smooth surface. Those capable of a fine polish are called marble, the more common uses of which are well known. The purest crystalline limestone is used in sculpture; the best quality being obtained from Carrara, Italy, and that called Parian from the island Paros.

Chalk, a useful formation, is a carbonate of lime. In some caves the dropping of calcareous water forms stalactites, which hang from the roof like immense icicles, and are often extended till they meet the accumulations below, called stalagmites, and form beautiful columns. Of the more than seven hundred crystals from this source alone, and of the many other varieties of minerals having much in common, and yet enough that is peculiar to distinguish them, no mention can be made. A careful reader and close observer will gather from familiar objects a fund of information of great value.

The parallel strata mentioned are not always horizontal, but sometimes nearly, if not quite perpendicular. Occasionally a ledge broken quite through separates, and the rock on one side of the fissure is either elevated or depressed, making what is called a fault.

The fissures crossing a bed of rock are often filled with a mineral entirely different from the rock itself. In some cases where the vein is small the foreign substance may have come in from above or laterally, deposited from water as in the case of stalactites. The larger fissures were evidently filled with the melted material thrust up from beneath.

The unstratified rocks are in masses, without fossils of animals or plants, and of igneous origin. Some of this class were probably formed later, and by the melting of secondary rocks, but most of them by the gradual cooling of the central mass containing the melted minerals embodied in them.

DYNAMIC GEOLOGY

Treats of the forces that move things on or beneath the earth’s surface. The Drift shows not a little confusion. Things are evidently in an abnormal condition, and strangely mixed. Some of the disturbing causes are obvious. Currents of the atmosphere and ocean have done much, but are not sufficient to account for all the phenomena. Boulders brought from ledges north of the great western lakes, are found scattered over all the western states, some much battered on the passage, others bearing only marks of long exposure to the elements. Deep furrows have been plowed in the rocks and hill tops over which they passed, at an elevation of thousands of feet above the level of the sea. Currents of water could never have lifted such huge masses from the lower to higher levels, or transported them any such distances. Icebergs or glaciers have evidently moved over the whole Drift region with fragments of rocks and pebbles frozen into their lower surface, that, like huge rasps, both cut away and polished the hardest rocks, at the same time bearing forward the boulders and whatever else chanced to be held in their cold embrace. There are other footprints of many and very great changes that have been wrought. Though many persons have erroneous impressions of the inequalities on the earth’s surface, the height of the loftiest mountains being but little when compared with the earth’s diameter, yet there is evidence that the normal condition has not been preserved. Large districts have, even within the historic period, been lifted far above their former level, and others sunk as much below. New islands have appeared in the midst of the sea, while others have sunk out of sight. Multitudes now live on what was once the bed of the sea, “in which were things innumerable, great and small beasts;” and ships sail over territory once covered with the habitations of living men. Rocks of immense thickness have been broken and the parts lifted into a vertical position, and many such great changes have taken place. What wrought them? It is safe to say that at least two forces have been operating, the one more gradual than the other. The cooling of the internal mass must cause contraction, which, in a globe of such dimensions, would be sufficient to break the strongest rocks constituting its shell. This force, when properly directed, might lift the rocks, and even throw them back on other strata of more recent formation. Then the expansive force of the gases within, when raised to their highest tension, is enough to cause earthquakes, and pour through the partially opened craters, or where the barriers are made less secure, floods of lava that are in time changed into rocks of that peculiar class. The vent will be found where the crust above the struggling giant is weakest, whether that be on the mountain top where the rocks had been shoved up into a vertical position, or at the bottom of the sea.

The dynamics of geology suggest problems of no ordinary interest, but our narrow limits forbid even a statement of them.

MINERALOGY

Is that branch of geology that treats of mineral substances, and teaches how to distinguish and classify them according to their properties. This is a wide field for investigation, and so fruitful that the temptation to linger in it is strong. Mining and work with the products of the mines engage the industry of so many that it would be especially pleasant to study with them a subject of such general interest. We relinquish that privilege, in order to state two or three things that seem thoroughly established by what is found written in the book of nature, and are in perfect accord with God’s later scriptures, the Bible, when rightly interpreted.

1. The first fact is the great age of the earth. Processes are plainly indicated that must have required not only thousands, but millions of years for our planet, before man, made in the image of God, entered it as the theater of his responsible activities. The facts of the carboniferous[4] period alone discredit, and utterly overthrow the theory which limits the days of creation to six of twenty-four hours each. The Bible gives the order of the successive creations, but does not fix the age of the things created. The word translated day often means an age or an indefinite number of years, as is seen by referring to the places where it is found. Give it this well established meaning in the first chapter of Genesis, and all is plain. There was time for millions of races of inferior creatures to live and die before the divine plans and works were consummated, and the earth became a suitable abode for the human race.

2. The second great fact is that all things were made on a plan, and in some connection. There are no isolated objects or superfluous parts in the physical world. The number may be countless, and the forms given them reveal an endless variety, but each has its connections, and all the parts are necessary to a perfect whole.

3. Another lesson is learned from the mute witnesses, which is that, while a long succession of races of animals, for which the earth, in its different stages of progress was a fit abode, existed, each higher in rank than its predecessor, the several races had distinctive characteristics, as the radiates, mollusks, articulates, and vertebrates. A lower species, when its purpose is served, becomes extinct, and is succeeded by a higher.

CHEMISTRY,

By analyzing compound and compounding simple substances, discovers their elementary properties, the forces that are resident in matter, and the laws that govern them. It demonstrates by experiments the affinity of ultimate particles, and of gases of unlike kinds for each other, an affinity which produces homogeneous compounds, often very unlike the elements that unite in forming them. The chemist has much to do with physical objects, but in handling them his appropriate business is to consider the changes produced by chemical attraction in all bodies, whether solid, liquid, or gaseous.

GEOGRAPHY

Is an ancient science, suitable for schools of all grades, and not for primary and intermediate departments alone. The child can treasure many of the facts that, if held in the memory, will be of use to him as he advances in years and knowledge, but his geography will benefit him little unless it is studied when his faculties are more mature. One who despises this study as beneath him, knows nothing yet of the important science as he ought.

PHYSICAL GEOGRAPHY

Has many things in common with both astronomy and geology, as it discusses the physical condition of the earth and its relations as a member of the solar system; describes its great natural divisions of land and water; and takes account of dynamic forces, such as aerial and oceanic currents, that are constantly causing important changes. The whole exterior structure of the earth, the phenomena of rain and dew, fog, frost, and snow, are geographical questions, to be discussed with special reference to the general laws or principles involved. It shows unity in the midst of diversity, and constancy of phenomena in the midst of apparent changes.

MATHEMATICAL GEOGRAPHY

Treats of the form and size of the earth, of the construction of globes to represent it; determines the latitude and longitude of places on its surface, and all geographical problems pertaining to numbers, distances, and magnitudes.

POLITICAL GEOGRAPHY

Describes, in a general way, the countries and nations of men as they are politically divided, defines their boundaries, and to some extent characterizes their social and civil institutions. A great advance has been made in this branch during the present century. People respecting whom little was known, have come into the family of nations. The maps have been changed, and generally in a way that indicates the rapid progress of civilization. Asia has been so thoroughly explored that our general knowledge of the country may be regarded as nearly complete. No great terra incognita remains in that quarter, though fuller and more precise knowledge respecting the people in some parts is yet much to be desired. The interior of Africa is still but partially known, though the work of discovery has been pushed forward with considerable enterprise, and a host of explorers have struggled to penetrate the mystery that enveloped, for ages, that great division of the globe. The Upper Nile country has been explored far beyond the region assigned on the maps to the “Mountains of the Moon,” and all know the intense anxiety that is to-day felt for the safety of General Gordon and his little garrison, still shut up in Khartoum.

The study of geography, rightly pursued, is remunerative, full of inspiration, and as intensely interesting as any in the whole circle of physical sciences.

BIOLOGY

Is scientific discourse about life and vital forces. We give it a high position in the circle, since vitality is superior to either chemical or mechanical laws, suspending or modifying them for the production of organized structures of plants and animals. Even vegetable biology confronts us with that mystery of mysteries, life, which is quite inexplicable. We can only say it is a peculiar, indefinable something, necessary to the existence of such organisms, and without which they soon sink in ruinous decay.

The living germ is the determining power that shapes the organic body, and every germ will have its own body. Under no possible culture can the acorn develop into an animal. It will produce an oak, a tree of its own species, and nothing else can grow from it. So also of the animal germ. The form or kind is as determinate while the embryo is yet in the egg, as it will ever be. The life once begun in everything that lives and grows, there is a power that takes hold of the elements nature has in store for it, and, by a most wonderful transformation, works them up into its own body; and this power of assimilation must forever distinguish it from all lifeless inorganic matter.

The mystery deepens when we notice that living things exist in generations. The plant has seed in itself for the production of another plant. It has life in itself, and power to vitalize its successors. The products of the field and the forest grow and mature, then wither and decay; but they have successors of the same kind.

So human beings exist in successive generations. One generation passeth away, and another cometh, and so the race lives on. While alike in their power of assimilation and reproduction, there is a wide difference between the vegetable and the animal. They have not the same organs, and do not subsist on the same food. The plant is constantly consuming carbonic acid, and giving out oxygen, while animals consume the oxygen, and restore to the atmosphere carbonic acid. The difference of their physical structure, and their different relations to inorganic matter, suggest a wide difference in the “bios” or life, that animates them. Just what that difference is, no one can tell. It is a question for which science furnishes no answer. In his physical organization man differs but little from the lower animals. In this he is brother to the beasts that perish, having the same nature, needs, and liabilities. If he is “fearfully and wonderfully made,” so are they; in agility and strength many of them far surpass him. His peculiarities of form and structure do not secure, and, it may be safely said, were not intended to secure physical superiority, but rather to fit the organization for the indwelling of the rational soul, that is his distinguishing characteristic.

PHYSICAL ASTRONOMY

Has been made the subject of much diligent research and study. Some facts respecting the physical elements and structure of the sun and planets have been ascertained with reasonable certainty, but much is still in doubt. Assuming that the essential properties of matter are the same everywhere, we may tell with assurance of what the sun and stars are made, provided all solar and stellar phenomena are explained by physical laws that are understood, and in operation around us. This has been done in part, but not so as to harmonize the views of all astronomers. Since the use of the spectroscope[5] results have been more satisfactory, and on some questions of much interest, conjecture and theory have given place to certainty. By the decomposition of sunbeams or pencils of solar light, the refracted rays show the presence of several distinct chemical elements. Finding by a qualitative analysis that there is iron, copper, zinc, nickel, sodium, and other terrestrial substances in the solar and stellar spectra, we know that they enter into the composition of those celestial bodies. But in what proportions or combinations they exist is not known.

METEOROLOGY AND AEROLITES.

Who has not seen a shooting star? For a moment the bright objects dart through greater or less spaces in the heavens, and then disappear. Those of inferior size give but little light, and are seldom seen unless the eye is, at the time, directed toward the space they traverse. Occasionally one flames out with such brilliancy as to light up, for a moment, the whole heavens. These are called meteors—a name quite proper for both classes, and only the very ignorant suppose any of them to be real stars. They come singly, two or three in an hour, or in showers, such as were witnessed in 1833. When of such size that they strike the earth before being consumed by their intense heat, they are aerolites, or meteoric stones. Great masses of these are found in different places, and show such a peculiar combination of their chemical elements as to distinguish them from all other stones; and mineralogists generally conclude they were not formed on the earth. Whence they come is not certainly known. That they were formed by an aggregation of their materials in our atmosphere seems incredible. Nor were they thrown off by some great convulsion, from the moon, with force sufficient to carry them beyond the attraction of that body. Perhaps most astronomers now believe, on what they think sufficient evidence, that the celestial spaces are occupied by innumerable small bodies moving round the sun, of whose nature and orbits nothing is certainly known. The earth, it is supposed, while making its annual circuit, must be constantly encountering them, and, as in passing rapidly through the upper region of the atmosphere they take fire and burn, the shooting star or meteor is simply the light of that flame. The mechanical production of heat, now well understood, shows why they burn. The rapid motion of the earth, especially if it be duplicated by that of the minute body striking through its atmosphere, would generate heat sufficient to quite consume the meteoroids; so that generally their solid substance is dissipated before they reach the ground. Sometimes the heated aerolite explodes when in such proximity to the earth that the fragments fall before they are consumed.

THE AURORA.

That most interesting atmospheric phenomena, the Aurora Borealis, though so familiar, has never been fully explained. It is rarely seen in equatorial latitudes, but increases in frequency and brightness as we go north, even to the arctic circle.

In this latitude all observers may at times notice two distinct forms of the aurora. The one, as we often see it, has a cloud-like appearance, with a soft radiance permeating it, and seems a vast, irregular patch of mellow light, ever changing, and at times showing a slightly reddish or purple tinge. It is more frequently seen near the northern horizon, having the form of a beautiful arch, the ends of the segment apparently resting on the horizon, and the middle, or crown, a few degrees above it. The other takes the form of streamers, reaching far up toward the zenith. Gently curved, like the celestial sphere on which they are projected, they are not stationary, but almost constantly in motion, but soon resuming their former position, spreading themselves out like immense flags, with their numerous silken folds, ever dancing, quivering, undulating, as if stirred by some gentle breeze, though all else seems in calm repose. To say that the phenomena are electrical, would, probably, not be the whole truth, though evidence is not wanting that the aurora is in some way connected with the electricity and magnetism of the earth and its atmosphere. Practical telegraphists testify that during a brilliant display of “northern lights” such strong, irregular currents of electricity pass along the wires that it is difficult to send a dispatch; at other times the currents are so strong that they can communicate without the battery.

There is, perhaps, about as much against the theory of a purely electrical origin, as in its favor, and, on the whole, we conclude that the Aurora Borealis is one of the things respecting which modern observations have suggested more difficulties than modern science is yet able to explain.