The Circle of Knowledge: A Classified, Simplified, Visualized Book of Answers

Part 6

Chapter 63,508 wordsPublic domain

Pegasus, the winged horse, sprang from the blood of the frightful Gorgon, Medusa, whom Perseus had slain not long before he rescued Andromeda from the sea-monster. According to the most ancient account, Pegasus became the horse of Jupiter, for whom he carried the thunder and lightning; but he afterward came to be considered the horse of Aurora, and finally of the Muses. Modern poets rarely speak of him except as connected with the Muses.

The Dragon, according to some of the poets, was the one that guarded the golden apples of the Hesperides; according to others, the monster sacred to Mars which Cadmus killed in Bœotia.

The Lyre is said to be the one which Apollo gave to Orpheus. After the death of Orpheus, Jupiter placed it among the stars at the intercession of Apollo and the Muses.

The Crown was the bridal gift of Bacchus to Ariadne, transferred to the heavens after her death.

Aquila is probably the eagle into which Merops was changed. It was placed among the stars by Juno. Some, however, make it the Eagle of Jupiter.

Cygnus or Cycnus, according to Ovid, was a relative of Phaëthon. While lamenting the unhappy fate of his kinsman on the banks of the Eridanus, he was changed by Apollo into a swan, and placed among the stars.

Sagittarius was said by the Greeks to be the Centaur Cheiron, the instructor of Peleus, Achilles and Diomed. It is pretty certain, however, that all the zodiacal constellations are of Egyptian origin, and represent twelve Egyptian deities who presided over the months of the year. Thus Aries was Jupiter Ammon; Taurus, the bull Apis; Gemini, the inseparable gods Horus and Harpocrates; and so on. The Greeks adopted the figures, and invented stories of their own to explain them.

Scorpio, in the Egyptian zodiac, represented the monster Typhon. Originally this constellation extended also over the space now filled by Libra.

Ophiuchus represents Æsculpius, the god of medicine. Serpents were sacred to him, probably because they were a symbol of prudence and renovation, and were believed to have the power of discovering herbs of wondrous powers.

Aquarius, in Greek fable, was Ganymede, the Phrygian boy who became the cup-bearer of the gods in place of Hebe.

Taurus, as has been stated above, was the Egyptian Apis. The Greeks made it the bull which carried off Europa. The Pleiades are usually called the daughters of Atlas, whence their name Atlantides. Milton speaks of them as “the seven Atlantic Sisters.”

According to one legend the seventh was Sterope, who became invisible because she had loved a mortal; according to another, her name was Electra, and she left her place that she might not witness the downfall of Troy, which was founded by her son, Dardanus.

The Hyades, according to one of several stories, were sisters of the Pleiades. The name probably means “the Rainy,” since their rising announced wet weather.

Cetus is said by most writers to be the sea-monster from which Perseus rescued Andromeda.

Orion was a famous giant and hunter, who loved the daughter of Oinopion, King of Chios. As her father was slow to consent to her marriage, Orion attempted to carry off the maiden; whereupon Oinopion, with the help of Bacchus, put out his eyes. But the hero, in obedience to an oracle, exposed his eye-balls to the rays of the rising sun, and thus regained his sight. The accounts of his subsequent life, and of his death, are various and conflicting. According to some, Aurora loved him and carried him off; but, as the gods were angry at this, Diana killed him with an arrow. Others say that Diana loved him, and that Apollo, indignant at his sister’s affection for the hero, once pointed out a distant object on the surface of the sea, and challenged her to hit it. It was the head of Orion swimming, and the unerring shot of the goddess pierced it with a fatal wound. Another fable asserts that Orion boasted that he would conquer every animal; but the earth sent forth a scorpion which destroyed him.

Canis Major and Minor are the dogs of Orion, and are pursuing the Hare.

The Twins, Castor and Pollux, the sons of Jupiter and Leda, are the theme of many a fable. They were especially worshipped as the protectors of those who sailed the seas, for Neptune had rewarded their brotherly love by giving them power over winds and waves, that they might assist the shipwrecked.

Leo, according to the Greek story, was the famous Nemean lion slain by Hercules. Jupiter placed it in the heavens in honor of the exploit.

The Hydra also commemorates one of the twelve labors of Hercules--the destruction of the hundred-headed monster of the Lernæan lake.

Virgo represents Astræa, the goddess of innocence and purity, or, as some say, of justice. She was the last of the gods to withdraw from earth at the close of “the golden age.”

Libra, or the Balance, is the emblem of justice, and is usually associated with the fable of Astræa.

Argo Navis is the famous ship in which Jason and his companions sailed to find the Golden Fleece.

This slight sketch of the leading fables connected with the constellations will serve to show how completely the Greeks “nationalized the heavens.”

SCIENTIFIC TERMS USED IN ASTRONOMY

=Astronomy= (_as-tron´om-i_). The science which treats of the heavenly bodies, explaining the motions, times and causes of the motions, distances, magnitudes, gravities, light, etc., of the sun, moon, and stars, the nature and causes of the eclipses of the sun and moon, the conjunction and apposition of the planets, and any other of their mutual aspects, with the times when they did or will happen.

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=Aberration= (_ab-er-ā´shun_). A small apparent motion of the fixed stars, occasioned by the progressive motion of light and the earth’s annual motion in its orbit. By this they sometimes appear twenty seconds distant from their true situation.

=Amplitude= (_am´pli-tud_). An arc of the horizon intercepted between the true east and west points and the center of the sun, or a star at its rising or setting.

=Anomaly= (_an-om´al-i_). The angular distance of a planet from its perihelion, as seen from the sun; either true, mean, or eccentric.

=Aphelion= (_af-ēl´yun_). That point of a planet’s orbit which is most distant from the sun.

=Apogee= (_ap´o-jē_). That point in the orbit of the moon which is at the greatest distance from the earth.

=Apparition= (_ap-par-ish´un_). The first appearance of a star or other luminary after having been obscured.

=Ap´pulse=. The approach of a planet towards a conjunction with the sun or any of the fixed stars.

=Apsis= (_ap´sis_). The two points of a planet’s orbit in which it is at its greatest and least distance from the sun.

=Aquarius= (_a-kwā´ri-us_). The eleventh sign of the zodiac, which the sun enters about the 21st of January.

=Asteroids= (_as´ter-oids_). The small planets that circulate between the orbits of Mars and Jupiter.

=Ax´is= (_ax´is_). The imaginary line passing through the center and poles of the earth, on which it performs its diurnal revolutions from west to east.

=Azimuth= (_az´im-uth_). An arc of the horizon intercepted between the meridian of the place and the vertical circle passing through the center of a celestial object.

=Can´cer=. The fourth sign of the zodiac, being that of the summer solstice, which the sun enters about the 21st of June.

=Capricorn= (_kap´ri-korn_). The tenth sign of the zodiac, which the sun enters about the 21st of December, at the winter solstice.

=Colure= (_kol´ur_). Two great circles, supposed to intersect each other at right angles in the poles of the world, one of them passing through the solstitial and the other through the equinoctial points of the ecliptic, viz., Cancer and Capricorn, Aries and Libra, dividing the ecliptic into four equal parts.

=Coma= (_kō´ma_). A dense, nebulous covering, which surround the nucleus or body of a comet.

=Com´et=. A member of the solar system, commonly consisting of three parts: the nucleus, the envelope or coma, and the tail; but one or more of these parts is frequently wanting.

=Conjunc´tion=. The meeting of two heavenly bodies in the same point or place in the heavens.

=Constella´tion=. A number of stars which appear as if situated near each other in the heavens, and are considered as forming a particular division.

=Cynosure= (_sin´o-shōōr_ or _sī´_). A name of the constellation Ursa Minor, or the Lesser Bear, which contains, in the tail, the pole star by which mariners are guided.

=Declination= (_dek-lin-a´shun_). Distance of any object from the celestial equator, either northward or southward.

=Disk=. The face or visible projection of a celestial body, usually predicated of the sun, moon, or planets; but the stars have also apparent disks.

=Eclipse´=. An obscuration or interception of the light of the sun, moon, or other luminous body.

=Eclip´tic=. The great circle of the heavens which the sun appears to describe in his annual revolution.

=Equa´tor=. The great circle of the sphere, equally distant from the two poles of the world, or having the same poles as the world.

=Equinox= (_ē´kwi-noks_). The precise time when the sun enters one of the equinoctial points, making the day and night of equal length.

=Faculae= (_fa´ku-lē_). Certain spots sometimes seen on the sun’s disk, which appear brighter than the rest of his surface.

=Fixed Stars=. Those which retain the same or very nearly the same position with respect to each other.

=Gal´axy=. The Milky-Way.

=Gemini= (_jem´i-nī_). The third sign or constellation in the zodiac, which the sun enters about the 21st of May.

=Geocentric= (_jē-o-sen´trik_) =Par´allax=. The apparent change of a body’s place that would arise from a change of the spectator’s station from the surface to the center of the earth.

=Ha´lo=. A luminous circle, usually prismatically colored round the sun or moon, and supposed to be caused by the refraction of light through crystals of ice in the atmosphere.

=Heliocentric= (_hē-li-o-sen´trik_) =Par´allax=. The arc of the great circle of the celestial sphere, drawn from the heliocentric to the geocentric place of a body.

=Heliometer= (_hē-li-om´e-ter_). An instrument for measuring with exactness the apparent diameter of the sun, moon, planets, etc.

=Hori´zon=. A circle touching the earth at the place of the spectator, and bounded by the line in which the earth and skies seem to meet.

=Le´o= (Lat., the Lion). The fifth sign of the zodiac which the sun enters about the 22d of July.

=Libra= (_lī´bra_), the Balance. The seventh sign of the zodiac, which the sun enters at the autumnal equinox, in September.

=Luna´tion=. The period of a revolution of the moon round the earth, or the time from one new moon to the next.

=Maculae= (_mak´u-lē_). Dark spots on the surfaces of sun and moon, and on some of the planets.

=Moon=. A secondary planet or satellite of the earth, whose light, borrowed from the sun, serves to dispel the darkness of night.

=Nadir= (_nā´dir_). The point of the heavens or lower hemisphere directly opposite the zenith.

=Neb´ulae= (_neb´u-lē_). Misty appearances among the stars, usually, but not always, resolved by telescope into myriads of small stars.

=Nodes= (_nōdes_). The two points in which the orbit of a planet intersects the ecliptic.

=Nuta´tion=. A vibratory motion of the earth’s axis, arising from periodical fluctuations in the obliquity of the ecliptic.

=Occulta´tion=. The hiding of a heavenly body from our sight by the intervention of some other of the heavenly bodies.

=Or´bit=. The path described by a heavenly body in its periodical revolution.

=Par´allax=. The change of place in a heavenly body in consequence of being viewed from different points.

=Penum´bra=. A partial shadow or obscurity on the margin of the perfect shadow in an eclipse, or between the perfect shadow, where the light is entirely intercepted, and the full light.

=Perigee= (_per´i-jē_). That point in the orbit of the sun or moon in which it is at the least distance from the earth.

=Perihelion= (_per-i-hē´li-on_). That part of the orbit of a planet or comet in which it is at its least distance from the sun.

=Plan´et=. The name given to a few bright and conspicuous stars which are constantly changing their apparent situations in the celestial sphere.

=Precession= (_pre-sesh´un_) =of the Equinoxes=. A continual shifting of the equinoctial points from east to west.

=Radius Vector=. An imaginary line joining the center of the sun and the center of a body revolving about it.

=Retrocession= (_rē-tro-sesh´un_) =of the Equinoxes=. The going backward of the equinoctial points.

=Sagittarius= (_saj-i-tā´ri-us_). One of the twelve signs of the zodiac, which the sun enters about November 22.

=Sat´ellite=. A small planet revolving round another planet.

=Scor´pio=. The eighth sign of the zodiac, which the sun enters about October 23.

=Selenography= (_sel-en-og´raf-i_). The description of the surface of the moon.

=Sign=. The twelfth part of the ecliptic.

=Solstice= (_sol´stis_). The time when the sun, in its annual revolution, arrives at that point in the ecliptic farthest north or south of the equator, or reaches its greatest northern or southern declination.

=Star=. An apparently small, luminous body in the heavens, that shines in the night, or when its light is not obscured by clouds or lost in the brighter effulgence of the sun.

=Sun=. The central body of our system, about which all the planets and comets revolve, and by which their motions are regulated and controlled.

=Taurus= (_taw´rus_). The second sign of the zodiac, which the sun enters about the 20th of April.

=Virgo= (_ver´go_). The sixth sign of the zodiac, which the sun enters in August.

=Ze´nith=. The point in the heavens directly overhead.

BOOK OF THE EARTH

THE EARTH AS A PLANET

ITS STRUCTURE: INTERIOR, CRUST, ROCKS, FOSSILS, HEAT

GEOLOGICAL VIEW OF GROWTH OF THE EARTH

SURFACE OF THE EARTH: LAND FORMS: CONTINENTS, ISLANDS, MOUNTAINS, PLAINS; WATER FORMS: SPRINGS, RIVERS, LAKES, OCEANS

CELEBRATED MOUNTAIN PEAKS AND RANGES

ATMOSPHERE, CLIMATE AND WEATHER

NATURAL WONDERS AND FORCES: VOLCANOES, EARTHQUAKES, GEYSERS, CAVERNS, WATERFALLS, WHIRLPOOLS, TIDES, DESERTS, OCEAN DEPTHS, CLOUDS, SEASONS, GLACIERS, ICEBERGS, SNOW, RAIN, HAIL, DEW, CORAL ISLANDS AND REEFS

DICTIONARY OF MINERAL PRODUCTS

TABLES FOR THE IDENTIFICATION OF MINERALS

GEMS AND PRECIOUS STONES

PRONOUNCING DICTIONARY OF SCIENTIFIC TERMS ABOUT THE EARTH

NUMEROUS ILLUSTRATIONS, CHARTS AND MAPS

BOOK OF THE EARTH

Science tells us that the Earth was once a shining star, a globe of liquid fire. As it cooled down, a crust formed over its surface, composed chiefly of rocks and metals. This crust was rent by the force of the gases shut up within, and thus the mountains, valleys, gorges, and volcanoes were formed. The Earth, indeed, is still upheaving and subsiding, but so slowly that we rarely feel it. Through these agencies the distribution of land and water on the surface of the earth has undergone great changes. The shape of the Earth is that of a sphere somewhat flattened at the poles, and it has a diameter of about 8,000 miles. The solid crust is called the _lithosphere_--which is surrounded by an envelope of air--the _atmosphere_--and in part by an envelope of water--the _hydrosphere_.

OUR EARTH: ITS STRUCTURE AND SURFACE

Our first glimpse of the earth as a planet shows it as a nebulous star, still intensely hot, and with no solid nucleus, rotating on its own axis, and at the same time revolving around the sun in a nearly circular orbit.

WHAT THE HEAT OF THE EARTH SHOWS

At first it seems hardly possible that the earth could have been a star. But, if we go down beneath the surface of the earth, we find that at a depth of forty or fifty feet there is very slight variation in temperature. When we go yet deeper, as in mines, we find that the earth grows hotter as we descend. The temperature increases on an average about one degree Fahrenheit for every sixty-four feet descent. But this amount is variable according to the locality, geological formation, and dip of strata. In the Calumet and Hecla Mine, observations show an increase of one degree in about every one hundred and twenty-five feet. At Paris, the water from a depth of 1794 feet has a temperature of eighty-two degrees; at Salzwerth, in Germany, from a depth of 2144 feet, a temperature of ninety-one degrees. Natural hot springs, rising from unknown depths, are sometimes scalding hot. One in Arkansas has a temperature of one hundred and eighty degrees.

At a depth of twenty miles, with this continual increase of temperature, the ground must be fully red-hot; and not very much farther down the heat must be sufficient to melt every known substance. The solid earth, then, is merely a thin crust, covering a sea of liquid fire below. The streams of lava poured forth from volcanoes are a proof of the existence of this molten mass beneath our feet.

WHAT CAUSES THE INTERNAL HEAT OF THE EARTH

If we examine the solid crust of the earth we shall not long be at a loss in regard to the origin of this internal heat. We are all familiar with the burning of coal. Now coal is mainly a substance called _carbon_, and when it burns it unites with _oxygen_, one of the gases in the air. Many rarer substances, such as silicon, and the metals magnesium, calcium, and sodium, are even more inflammable than carbon, and in burning give rise to solid products. Now the rocks in the earth are found to be made up almost wholly of these very inflammable substances combined with oxygen. The solid portions of the earth, then, are nothing but the ashes and cinders of a great conflagration. Even the waters are made up of hydrogen, one of the most inflammable substances, united with this same oxygen, and, strange as it may seem, they too, are the products of combustion. When, therefore, the materials of which the earth is formed were burning, our planet must have been a fiery star, and the great heat must have reduced all the products of the conflagration to a liquid state.

HOW THE EARTH’S CRUST WAS FORMED

When the fire went out for lack of fuel the mass began to cool at the surface, and a solid crust was finally formed, which with the lapse of time became thicker and thicker. This crust shut in the steam and gases generated in the fiery ocean underneath; and these, acting upon the crust with enormous pressure, heaved it into ridges. At times the strain caused the crust to crack, and forced the melted mass up through it, and in this way hills and mountains were formed. The thicker the crust the greater the strain it would bear before it gave way, and the greater the amount of molten matter driven out through the rent. The highest mountains, then, are the last that were uplifted. In some cases the openings thus made in the crust were never completely closed, and thus volcanoes were formed. These act like safety-valves, and prevent the forces within from accumulating sufficiently to cause fresh rents. But notwithstanding the relief thus given to the pent-up forces, they still manifest themselves in earthquakes.

SHAPE OF THE EARTH A SPHEROID

Like all other planets, the earth is a solid sphere that has undergone a slight flattening at the opposite extremities or poles of the axis of revolution. More accurately, it is an oblate spheroid generated by the rotation of an ellipse about its minor axis. Such a figure would be assumed by a sphere of liquid rotating about a diameter, centrifugal force acting most vigorously at the equator, and tending to overcome the internal forces that keep the molecules together.

SIZE AND DENSITY OF THE EARTH