Part 2
II. ENGLISH AND AMERICAN LITERATURE -- OUTLINE CHARTS OF ENGLISH AND AMERICAN AUTHORS -- DICTIONARY OF LITERARY ALLUSIONS: FAMOUS BOOKS, POEMS, DRAMAS, LITERARY CHARACTERS, PLOTS, PEN NAMES, LITERARY SHRINES AND GEOGRAPHY, AND OTHER MISCELLANY -- PRONOUNCING DICTIONARY OF MYTHOLOGY: GODS, HEROES, AND MYTHICAL WONDER TALES -- CHART OF GREEK AND ROMAN MYTHS, THEIR ORIGIN, RELATIONSHIP AND DESCENT.
=⁂Books of Reference.=--LANGUAGE.--Sayce: _Introduction to the Science of Language_. Whitney: _Language and the Study of Language_. Paul: _Principles of the History of Language_. Muller: _Science of Language_. Skeat: _Philosophy_. Jesperson: _Progress in Language, with Special Reference to English_. Giles: _Manual of Comparative Philosophy for Classical Students_. Oertel: _Lectures on the Study of Language_. Sweet: _Primer of Spoken English_. Skeat: _Etymological Dictionary of the English Language_. Sweet: _Grammar, Logical and Historical_. Lewis: _Applied English Grammar_. Genung: _Practical Elements of Rhetoric_. Gummere: _Poetics_. Wendell: _English Composition_. Palmer: _Self-Cultivation in English_. Kittredge: _Words and their Ways in English Speech_. Trench: _Study of Words_. Fernald: _Synonymns and Antonymns_.
LITERATURE.--Jevons: _History of Greek Literature_. Mahaffy: _Greek Literature_. Crutwell: _History of Roman Literature_. Fortier: _History of French Literature_. Robertson: _History of German Literature_. Garnett: _Short History of Italian Literature_. Symonds: _Italian Renaissance_. Horn: _History of Scandinavian Literature_ and _Jewish Encyclopedia_. Morley: _Library of English Literature_. Brooke: _History of English Literature_. Ward: _English Poets_. Gosse: _Short History of English Literature_. Tyler: _History of American Literature_. Matthews: _History of American Literature_. Stedman: _An American Anthology_. Johnson: _Elements of Literary Criticism_. Warner: _Library of Universal Literature_.
DICTIONARIES.--Webster: _New International Dictionary_. Worcester: _Dictionary of the English Language_. Funk and Wagnalls: _Standard Dictionary_. Whitney: _The Century Dictionary_. Murray: _Oxford English Dictionary_. Wright: _Dialect Dictionary_.
BOOK OF THE SCIENCES AND INVENTION
DEVELOPMENT OF THE SCIENCES IN PARALLEL OUTLINES -- PRACTICAL MATHEMATICS -- ARITHEMATIC AND ITS MODERN APPLICATIONS -- THE ARITHMETIC OF BUSINESS, COMMERCIAL AND INDUSTRIAL TRANSACTIONS -- CORPORATIONS, STOCKS AND BONDS -- TABLE OF COMMERCIAL LAWS -- WEIGHTS AND MEASURES -- PHYSICS: LAWS AND PROPERTIES OF MATTER -- MECHANICS AND INVENTIONS -- SOUND -- HEAT -- LIGHT AND COLOR -- ELECTRICITY AND MAGNETISM -- CHEMISTRY: THEORY OF CHEMISTRY -- TABLE OF THE CHEMICAL ELEMENTS -- THE CHEMISTRY OF COMMON THINGS -- REMARKABLE INVENTIONS AND DISCOVERIES -- RECENT SCIENTIFIC PROGRESS, X-RAYS AND RADIUM, WIRELESS TELEGRAPHY, WIRELESS TELEPHONE, AEROPLANES, SUBMARINES, AIRSHIPS, AND EXPLOSIVES.
=⁂Books of Reference.=--BIOLOGY.--Brooks: _Foundations of Zoology_. Morgan: _Animal Behavior_. Pearson: _The Grammar of Science_. Spencer: _Principles of Biology_. Thomson: _The Science of Life_. Verworn: _General Physiology_. Weismann: _The Germ-Plasm_.
PHYSICS.--Ames: _General Physics_. Ames and Bliss: _Manual of Experiments_. Hoadley: _Measurements in Magnetism and Electricity_. Preston: _Theory of Heat_ and _Theory of Light_. Poynting and Thomson: _Heat_. Tyndal: _Light_. Schuster: _Theory of Optics_. Barker: _Physics_. Merrill: _Theoretical Mechanics_. Helmholtz: _Sensations of Tone_. Kapp: _Electric Transmission of Energy_. Crocker: _Electric Lighting_. Sewell: _Elements of Electrical Engineering_. Jackson: _Elements of Electricity and Magnetism_ and _Alternating Currents and Alternating Current Machinery_.
CHEMISTRY.--Remsen: _Introduction to the Study of Chemistry_ and _Inorganic Chemistry_. Roscoe: _Lessons in Elementary Chemistry_. Wurtz: _Elements of Modern Chemistry_. Ostwald: _Inorganic Chemistry_. Alexander Smith: _Laboratory Outline of General Chemistry_ and _General Inorganic Chemistry_. Wiley: _Chemistry of Foods_ and _Agricultural Chemistry_. Roscoe and Schorlemmer: _Treatise on Chemistry_. Watts: _Dictionary of Chemistry_. Thorp: _Industrial Chemistry_.
(Abridged in the Concise Edition.)
BOOK OF THE HUMAN BODY
ITS STRUCTURE -- ORGANIZATION INTO SYSTEMS -- FUNCTIONS -- SPECIAL SENSES -- NERVOUS SYSTEM -- PERSONAL HYGIENE -- PREVENTION OF DISEASE -- INTERDEPENDENCE OF BODY AND MIND -- EUGENICS -- ILLUSTRATIONS AND CHARTS.
=⁂Books of Reference.=--Morris: _Treatise on Anatomy_. Gray: _Anatomy_. Davidson: _Human Body and Health_. Martin: _Human Body_. Huxley and Youmans: _Elements of Physiology and Hygiene_. Wilson: _The Cell in Development and in Inheritance_. Thomson: _Heredity_. Loeb: _Comparative Physiology of the Brain and Comparative Psychology_. Sternberg: _Manual of Bacteriology_.
(Abridged in the Concise Edition.)
BOOK OF BIOGRAPHY
BIOGRAPHICAL CHART SHOWING THE WORLD’S MASTERS OF ACHIEVEMENT BY CENTURIES.
CHRONOLOGICAL DICTIONARY OF BIOGRAPHY: (_a_) THE WORLD’S IMMORTALS, specially treated; (_b_) PRESENT-DAY BIOGRAPHIES.
(The Biographical Chart only is included in the _Concise_ edition.)
=⁂Books of Reference.=--Philips: _Dictionary of Biographical Reference_. Vincent: _Dictionary of Biography_. Thomas: _Dictionary of Biography_. Appleton: _Dictionary of American Biography_; _Dictionary of National Biography_; _Who’s Who in Great Britain_; _Who’s Who in America_. Ruoff: _Masters of Achievement_; _American Statesmen Series_; _American Men of Letters_; _English Statesmen Series_; _English Men of Letters_. Smith: _Dictionary of Christian Biography_.
(Omitted in the Concise Edition.)
BOOK OF THE CHILD WORLD
PLAYLAND -- STORYLAND -- NATURE-LAND -- SCHOOL-LAND: SIMPLE LESSONS ABOUT WORDS, READING, WRITING, NUMBERS, ETC. -- MANNERS AND CONDUCT -- THE PARENT AND CHILD -- THE OUTLOOK UPON LIFE -- EDUCATION AND MORAL GROWTH -- CARE OF THE BODY.
=⁂Books of Reference.=--PRIMARY EDUCATION.--Arnold: _Rhythms_. Barnard: _Kindergarten and Child-Culture Papers_. Blow: _Educational Issues_; _Letters to a Mother_; _Symbolic Education_. Froebel’s translated _Mother-Play Songs_. Froebel: _Education of Man_; _Education by Development_; _Last Volumes of Pedagogics_; _Pedagogics of the Kindergarten_. Hailman: _Laws of Childhood_. Harrison: _A Study of Child-Nature_; _Kindergarten Building Gifts_; _Misunderstood Children_; _Two Children of the Foothills_. Hughes: _Educational Laws_. Peabody: _Kindergarten Lectures_. Snider: _Commentary on Froebel’s Mother-Play Songs_; _Life of Froebel_; _Psychology of the Play-Gifts_. Vanderwalker: _The Kindergarten in American Education_. Von Bulow: _The Child_; _Reminiscences of Froebel_.
(Abridged in the Concise Edition.)
LIST OF ILLUSTRATIONS
Color Plates
MARVELS OF THE EARTH’S ROTATION AND FORCES PROUD COLOR BEAUTIES OF THE LAND OF FLOWERS THREE CELEBRATED PICTURES OF ANIMAL FAVORITES WASHINGTON, AMERICA’S CITY BEAUTIFUL ARCHITECTURAL GLORIES OF FAMOUS LANDS FAMOUS HISTORICAL PICTURES BY ORIENTAL ARTISTS TENNYSON’S BEAUTIFUL “LADY OF SHALOTT” “OPEN SESAME!” ALI BABA AT THE CAVE PICTURE DIAGRAMS OF EYE AND EAR THE FIERY FURNACE THAT PURIFIES BESSEMER STEEL “THE IDES OF MARCH” FAMOUS MASTERPIECES BY FAMOUS PAINTERS
(Only six Color Plates are included in the single volume edition)
Diagrams, Maps and Charts
COLOR DIAGRAM SHOWING THE OCEAN BEDS DIAGRAM OF ORBITS OF THE PLANETS PICTURE DIAGRAM OF THE MOON’S PHASES STAR CHARTS OF THE CHIEF CONSTELLATIONS MAPS OF THE CHIEF CONSTELLATIONS CHART OF THE MILKY WAY DIAGRAMS SHOWING FORMATION OF ECLIPSES DIAGRAM SHOWING A BISECTION OF THE EARTH CHART SHOWING THE GEOLOGICAL GROWTH OF THE EARTH GEOLOGICAL MAP OF THE UNITED STATES MAPS SHOWING RELATIVE SIZE OF ISLANDS OF THE WORLD DIAGRAM OF THE WORLD’S FAMOUS RIVERS AND MOUNTAINS MAPS SHOWING RELATIVE SIZE OF LAKES DIAGRAMS EXPLAINING THE SEASONS, DAY AND NIGHT PICTORIAL CHART OF CLOUD FORMATIONS MAP SHOWING DISTRIBUTION OF PLANT LIFE MAP SHOWING RANGE OF ANIMAL LIFE 16 MAPS IN COLOR SHOWING THE PROGRESS OF GEOGRAPHICAL DISCOVERY 2 PICTURE MAPS PRESENTING A PANORAMIC VIEW OF PARIS 5 PICTURE MAPS GIVING A PANORAMA OF THE RIVER RHINE PICTURE DIAGRAM SHOWING PARTS OF A LOCOMOTIVE PICTURE DIAGRAM OF SUBMARINE PICTURE DIAGRAM EXPLAINING WIRELESS TELEGRAPHY PICTURE DIAGRAM EXPLAINING AN ELECTRIC BATTERY PICTURE DIAGRAM SHOWING HOW ELECTRICITY IS GENERATED PICTURE DIAGRAM EXPLAINING RADIOACTIVITY MAP OF PANAMA CANAL AND CONNECTIONS
Other Full Page and Text Illustrations
These include hundreds of beautiful and instructive reproductions illustrative of the heavens, earth, minerals, plants and plant products, animal life, races and peoples, famous examples of architecture, scenes in great cities, historic shrines and ruins, mythology, science, marvels of mechanism, great works of engineering, monuments, industries, etc., as well as numerous photographic and art pictures of famous persons and episodes in the history of progress.
BOOK OF THE HEAVENS
_Descriptive and Explanatory_
THE UNIVERSE: ITS MAGNITUDE AND MEANING
THE SOLAR SYSTEM: SUN, PLANETS, MOON, CONSTELLATIONS, STARS, COMETS, METEORS, NEBULÆ, AND OTHER WONDERS OF THE SKIES
ORIGIN OF THE WORLDS: THE NEBULAR HYPOTHESIS
ECLIPSES: CAUSES AND EXPLANATION
MYTHOLOGY OF THE CONSTELLATIONS
DICTIONARY OF SCIENTIFIC TERMS
STAR CHARTS AND MAPS
NUMEROUS ILLUSTRATIONS AND TABLES
[Illustration: =DIAGRAM SHOWING RELATIVE ORBITS OF THE PLANETS AROUND THE SUN=
1. Crowded group of stars seen in the constellation Hercules. 2. Beautiful circular group of stars in Aquarius. Very brilliant toward the center. 3-4. Fan-shaped groups of stars, frequently to be observed. 5. Round nebula of Ursa Major. 6. A fine star in Gemini with a great, oval atmosphere. 7. Star in Leo Major in the middle of nebula with very pointed ends. 8-9. Nebulæ with luminous trains like the tail of a comet. 10. Two stars in Canes Venatici joined by elliptical nebula. 11. Elliptical nebula in Sagittarius with a star in each of the foci. 12-13. Round nebula in Auriga with three stars in a triangle. 14. Great nebula in Andromeda. 15. Comet of 1819, of remarkable size. 16-17. Great comet of 1811. 18. Surface of the planet Mars, showing the supposed continents and seas. 19. Disk of the great planet Jupiter with its dark streaks and masses. 20. The wonderful planet Saturn with its remarkable rings.
=Explanation of Figures in Diagram=
=Rate at which the Planets Travel=]
BOOK OF THE HEAVENS
THE UNIVERSE -- THE SOLAR SYSTEM -- PLANETS -- SUN -- MOON -- CONSTELLATIONS -- STARS -- COMETS -- METEORS -- NEBULÆ -- NEBULAR HYPOTHESIS -- ECLIPSES -- MYTHOLOGY OF THE CONSTELLATIONS -- DICTIONARY OF SCIENTIFIC TERMS USED IN ASTRONOMY.
[Illustration: =HOW THE PLANETS WOULD APPEAR IF GROUPED IN SPACE=
In the above picture we have represented the planets of the Solar System as we should see them from the earth if the human eye could grasp a space of such immensity. The spectator is supposed to be standing on the earth, and the moon is in the foreground, 240,000 miles away. The planets are in their order outward from the sun, and vary in distance from 40,000,000 miles, in the case of Mars, to 2,700,000,000 miles in the case of Neptune. From the bottom upward, the planets are Mercury, Venus, Mars, Jupiter, Saturn and its rings, Uranus and Neptune.]
THE WORLDS IN THE SKIES
The earth upon which we live is only one of many worlds that whirl through space. If we are to understand our own world, we must first learn something about the worlds in the skies. These bodies are arranged in groups, or systems, sweeping through circuits that baffle measurement; and such is the magnitude of the boundless space they occupy that our entire solar system is only a point in comparison. To this vast expanse of worlds, and systems and space we give the general name _Universe_.
THE SOLAR SYSTEM AND ITS MEMBERS
First in importance to us in this immense space filled with stars is what astronomers call the Solar System, so-called because the sun is its center. It contains the planets, eight in number, of which our earth is one. They have been named after the ancient deities; the two interior ones, Mercury and Venus, and the exterior ones, Mars, Jupiter, Saturn, Uranus, and Neptune; the first three being smaller than our earth, and the remainder a great deal larger.
Mercury and Venus are known to be _interior_ planets, that is, planets between us and the sun, because they appear to swing on either side of the sun. Mercury very seldom leaves the sun sufficiently to rise so early before the sun, or set so late after him, as to be visible. Venus, however, gets so far away as to be seen long after sunset or before sunrise, and is called the Evening or Morning star, accordingly.
Besides the planets there are other members of the system, namely, _comets_ and _falling stars_, which will be mentioned again more fully hereafter. All these bodies form a sort of family, having the sun for their head. The illustrations and drawings on separate pages give a view of the entire system.
COMPARATIVE SIZE. The size of the planets, in general, increases with their distance from the sun. The four composing the first group are all comparatively small, the earth being the largest. Those of the second group are all of great size. Jupiter, the largest, is not less than 1,390 times as large as the earth; but as it is much less dense, the amount of matter it contains is only a trifle more than 337 times that of the earth. All the planets together equal but one seven-hundredth part of the mass of the sun.
The SATELLITES, except our moon, and the two satellites of Mars, belong wholly to the second group of planets. Jupiter has eight; Saturn eight and several revolving rings; Uranus has four, and possibly more; while Neptune, so far as known with certainty, has but one.
MOVEMENTS WITHIN THE SOLAR SYSTEM
ROTARY MOTION. The sun, all the primary planets, and their satellites, as far as known, rotate from west to east. Each rotation constitutes a day for the rotating body. The central line of rotary motion is called the axis of rotation, and the extremities of the axis are called the Poles.
REVOLUTION AROUND THE SUN. All the primary planets and asteroids revolve around the sun in the direction of their rotation, that is from west to east; and the planes of the orbits in which they revolve coincide very nearly with the plane of the sun’s equator. One revolution around the sun constitutes the year of a planet.
All the satellites, except those of Uranus and perhaps Neptune, also revolve from west to east.
Most of the comets revolve around the sun in very irregular and elongated orbits, only a few having their entire orbit within the planetary system. Some so move that after having entered our system and made their circuit around the sun, they seem to leave it, never to return.
[Illustration: The Egyptian Planisphere containing the Zodiacal signs, with the Southern constellations, according to Kircher.]
[Illustration: The Egyptian Planisphere containing the Zodiacal signs, with the Northern constellations, according to Kircher.]
Since the orbits of the planets are in most cases not far removed from the plane of the ecliptic, they are to be seen in a comparatively narrow belt of the heavens called,
THE ZODIAC. The belt of the sky which occupies 8° on each side of the ecliptic is called the Zodiac, and it is within this belt that the moon and the chief planets confine their movements, as none of their orbits is inclined to that of the earth by more than 8°. The Zodiac, which circles the celestial sphere, is divided into twelve signs each of which occupies 30°, and roughly coincides with a constellation. The following lists give the signs of the Zodiac, with the seasons in which the sun passes through each of them:
Spring: Aries the Ram; Taurus the Bull; Gemini the Twins.
Summer: Cancer the Crab; Leo the Lion; Virgo the Virgin.
Autumn: Libra the Balance; Scorpio the Scorpion; Sagittarius the Archer.
Winter: Capricornus the Goat; Aquarius the Water-bearer; Pisces the Fishes.
Owing to the precession of the equinoxes, the signs of the Zodiac do not now correspond with the constellations of which they bear the names. Thus the sign Aries, in which the sun is seen on March 21st as it passes the vernal equinox, with which the solar year begins, is now in the constellation of Pisces, and in the course of the next 23,000 years it will move steadily backward through the constellations until it returns to the Ram, where it stood when its name was first given to it.
KEPLER’S CELEBRATED LAWS OF PLANETARY MOVEMENTS
The laws under which the planets move were discovered through the genius of John Kepler, and are known as Kepler’s Laws of Planetary Motion. Kepler derived these laws from observation only, but Newton first explained them by showing that they were the necessary consequences of the laws of motion and the law of universal gravitation.
KEPLER’S FIRST LAW states: “The earth and the other planets revolve in ellipses with the sun in one focus.”
KEPLER’S SECOND LAW states: “The radius vector of each planet moves over equal areas in equal times.”
KEPLER’S THIRD LAW states: “The squares of the periodic times of the planets are in proportion to the cubes of their mean distances from the sun.”
[Illustration: =DIAGRAMS ILLUSTRATING KEPLER’S FIRST TWO LAWS OF PLANETARY MOTION=
The diagram on the top illustrates the ellipse, and explains the first and second laws. The picture-diagram on the bottom illustrates the second law, which is that, as the planet moves round the sun, its radius vector describes equal areas in equal times. That is to say, a planet moves from A to B in the same time as it takes to move from C to D.]
These laws cannot be fully understood without some acquaintance with mathematics. They may, however, be briefly explained for the comprehension of the non-mathematical reader. The figure in the diagram is an ellipse--what is known in popular language as an oval--which is symmetrical about the line AB, known as its major axis. It has two foci, S and S₁. The fundamental law of the ellipse is that if we take any point P on it, and join this point by a straight line to the two foci, then the sum of these two lines SP and S₁P is always the same--SP + S₁P = C.
The second law is rather less easy to understand. The _radius vector_ is the line joining the sun to the planet at any moment; if we suppose the sun to be at the focus S, and P to be the planet, the radius vector at various positions of the planet will be represented by the lines SP, SP₁, SP₂, and so on. If the positions P, P₁, P₂, and so on, represent those which the planet occupies after equal periods of time--say, once a month--then the sectors of the ellipse bounded by each pair of lines, SP and SP₁, SP₁ and SP₂, will be equal. If a planet were to move in a circle round the sun, it is obvious that this law would imply that it moved with a uniform speed; but since the curvature of the ellipse varies in every part of its course, so must the speed of the planet, in order that its radius vector may describe equal areas in equal times. The planet will, in fact, be moving faster when it is near the sun, as at P, than when it is far off from the sun, as at P₂.
The third law shows that there is a definite numerical relation between the motions of all the planets, and that the time which each of them takes to complete its orbit depends upon its distance from the sun.
On his discovery of his third law Kepler had written: “The book is written to be read either now or by posterity--I care not which; it may well wait a century for a reader, as God has waited six thousand years for an observer.” Twelve years after his death, on Christmas Day, 1642, near Grantham, England, the predestined “reader” was born. The inner meaning of Kepler’s three laws was brought to light by Isaac Newton.
THE GIGANTIC SUN AND HIS FUNCTION IN THE SOLAR SYSTEM
The great luminary which warms, lights, and rules the solar system is, like the majority of its fellow stars, a gigantic bubble. In other words, it is a globe of glowing gas, which is nowhere solid, though the immense pressure which must exist in its interior probably causes this gas to assume there a density greater than that of any solid which we know.
[Illustration: =A PHOTOGRAPH OF THE SUN, SHOWING THE CLOUDS OF FIERY VAPOR WHICH SURROUND IT=]
DIMENSIONS OF THE SUN. The sun appears to human vision as a brilliant globe of a little more than half a degree in diameter. It is about the same apparent size as the moon, since the size of the sun is to that of the moon very nearly in the same proportion as their relative distances from the earth. In reality, however, the sun is a gigantic orb, so huge that if the earth were at its center the whole orbit of the moon would lie well within its circumference. The diameter of the sun is about 866,500 miles.
The mass of the sun is about 332,000 times that of the earth, but its specific gravity is only about a quarter that of the earth, 1.41, if that of water be taken as unity. The mean distance of the sun from the earth is about 92,800,000 miles; but, as the earth’s orbit is not circular but elliptic, this distances varies by about 3,000,000 miles, being smallest in January and greatest in July.
THE PHYSICAL CONDITION of the sun is very different from that of the earth, though we know it is composed of very similar materials. The white-hot surface that we see, called the _photosphere_, is believed to be largely a shell of highly heated metallic vapors surrounding the unseen mass beneath. Dark spaces seen in the photosphere are known as _sun-spots_, and these are often surrounded by brighter patches, termed _faculæ_. Above the photosphere a shallow envelope of gases, rising here and there into huge prominences, and known as the _chromosphere_, is seen in red tints when the sun is totally eclipsed. Beyond the chromosphere, there is also seen, at the same time, a faint but far more extensive envelope called the _corona_.
[Illustration: This diagram illustrates the theory that sun-spots are formed by fragments struck from Saturn’s rings (which are in themselves nothing more than a great meteoric swarm) by the swarm of meteors known as the Leonids, which fragments fall into the solar furnace at a speed of four hundred miles a second.]
The sun’s rays supply light and heat not only to the earth, but also to the other planets which revolve round it. Its attraction confines these planets in their orbits and controls their motions.
THE MOON--THE EARTH’S ONLY SATELLITE
THE MOON, the satellite of the earth, is the nearest to us of all the heavenly bodies, being at a mean distance of 240,000 miles. Its diameter is 2,153 miles and, its density being little more than half that of the earth, the force of gravity at its surface is very much less than that at the surface of the earth. A body which weighs a pound here would only weigh about two and one-half ounces if taken to the moon.
[Illustration: =THE SYSTEM OF MARS AND ITS MOONS CONTRASTED WITH THAT OF THE EARTH AND MOON=
In this diagram the markings on the earth and Mars are to scale, the orbits of the planets are seen in perspective and the measurements are according to Prof. Percival Lowell.]
THE MOON’S ORBIT. Her path is approximately an ellipse with the earth in one focus. Its apparent motion in the sky is from west to east, but she moves much faster than the sun, taking about twenty-seven days eight hours to travel all round the earth. The time between two successive new moons (synodic period or lunation) is twenty-nine and one-half days. The reason of the difference is that the sun moves slowly in his annual course through the stars in the same direction as the moon, which therefore in its revolution round the earth has to overtake him when it returns. The moon rotates on its axis in the same time as it performs a revolution in its orbit; hence the same half is always turned toward us.
When the moon in her orbit lies between the sun and the earth, she is said to be in _conjunction_ with the sun; when the earth is between the moon and the sun, the moon is said to be in _opposition_ to the sun. At either of the two points midway from conjunction and opposition, i. e. 90° from conjunction or opposition, the moon is said to be in _quadrature_.