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- Herausgeber: Science & Technology Publishing
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Recreations in Astronomy With Directions for Practical Experiments and Telescopic Work is a comprehensive and engaging guide to the wonders of the night sky, written by Henry White Warren. Designed for both amateur astronomers and curious readers, the book offers a fascinating blend of scientific explanation, practical instruction, and philosophical reflection. It covers a wide range of astronomical topics, from the basic principles of celestial mechanics to the detailed observation of planets, stars, and nebulae. The author provides clear and accessible explanations of complex phenomena such as eclipses, comets, meteors, and the motions of the solar system, making the subject approachable for readers without a scientific background. A distinctive feature of the book is its emphasis on hands-on learning. Warren includes numerous practical experiments and detailed directions for telescopic observation, encouraging readers to actively engage with the material and experience the thrill of discovery for themselves. The book is richly illustrated with diagrams and star charts, aiding in the identification of constellations and celestial objects. Throughout, Warren’s writing is infused with a sense of wonder and reverence for the universe, inviting readers to contemplate the grandeur and mystery of the cosmos. Recreations in Astronomy not only serves as a practical manual for stargazing but also as a source of inspiration, blending scientific knowledge with poetic appreciation. It is an ideal companion for anyone seeking to deepen their understanding of astronomy, whether observing the heavens with the naked eye or through the lens of a telescope. With its blend of instruction, entertainment, and philosophical insight, this classic work remains a valuable resource for students, educators, and enthusiasts of all ages.
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Seitenzahl: 314
Veröffentlichungsjahr: 2025
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RECREATIONS IN ASTRONOMY
WITH
DIRECTIONS FOR PRACTICAL EXPERIMENTS AND TELESCOPIC WORK
BY
HENRY WHITE WARREN, D.D.
AUTHOR OF "SIGHTS AND INSIGHTS; OR, KNOWLEDGE BY TRAVEL," ETC.
WITH EIGHTY-THREE ILLUSTRATIONS AND MAPS OF STARS
ΤΗΙ ΨΥΧΗΙ ΤΗΙ ΑΓΑΠΗΤΗΙ ΑΣΤΡΑΠΤΟΥΣΗΙ ΚΑΙ ΙΣΑΓΓΕΔΩΙ
PREFACE.
All sciences are making an advance, but Astronomy is moving at the double-quick. Since the principles of this science were settled by Copernicus, four hundred years ago, it has never had to beat a retreat. It is rewritten not to correct material errors, but to incorporate new discoveries.
Once Astronomy treated mostly of tides, seasons, and telescopic aspects of the planets; now these are only primary matters. Once it considered stars as mere fixed points of light; now it studies them as suns, determines their age, size, color, movements, chemical constitution, and the revolution of their planets. Once it considered space as empty; now it knows that every cubic inch of it quivers with greater intensity of force than that which is visible in Niagara. Every inch of surface that can be conceived of between suns is more wave-tossed than the ocean in a storm.
The invention of the telescope constituted one era in Astronomy; its perfection in our day, another; and the discoveries of the spectroscope a third—no less important than either of the others.
While nearly all men are prevented from practical experimentation in these high realms of knowledge, few have so little leisure as to be debarred from intelligently enjoying the results of the investigations of others.
This book has been written not only to reveal some of the highest achievements of the human mind, but also to let the heavens declare the glory of the Divine Mind. In the author's judgment, there is no gulf that separates science and religion, nor any conflict where they stand together. And it is fervently hoped that anyone who comes to a better knowledge of God's works through reading this book, may thereby come to a more intimate knowledge of the Worker.
I take great pleasure in acknowledging my indebtedness to J. M. Van Vleck, LL.D., of the U.S. Nautical Almanac staff, and Professor of Astronomy at the Wesleyan University, for inspecting some of the more important chapters; to Dr. S. S. White, of Philadelphia, for telescopic advantages; to Professor Henry Draper, for furnishing, in advance of publication, a photograph of the sun's corona in 1878; and to the excellent work on "Popular Astronomy," by Professor Simon Newcomb, LL.D., Professor U. S. Naval Observatory, for some of the most recent information, and for the use of the unequalled engravings of Jupiter, Saturn, and the great nebula of Orion.
CONTENTS.
CHAP.
I.
CREATIVE PROCESSES
II.
CREATIVE PROGRESS
Constitution of Light
Chemistry of Suns revealed by Light
Creative Force of Light
III.
ASTRONOMICAL INSTRUMENTS
The Telescope
The Reflecting Telescope
The Spectroscope
IV.
CELESTIAL MEASUREMENTS
Celestial Movements
How to Measure
V.
THE SUN
What the Sun does for us
VI.
THE PLANETS, AS SEEN FROM SPACE
The Outlook from the Earth
VII.
SHOOTING-STARS, METEORS, AND COMETS
Aerolites
Comets
Famous Comets
Of what do Comets consist?
Will Comets strike the Earth?
VIII.
THE PLANETS AS INDIVIDUALS
Vulcan
Mercury
Venus
The Earth
The Aurora Borealis
The Delicate Balance of Forces
Tides
The Moon
Telescopic Appearance
Eclipses
Mars
Satellites of Mars
Asteroids
Jupiter
Satellites of Jupiter
Saturn
Rings of Saturn
Satellites of Saturn
Uranus
Neptune
IX.
THE NEBULAR HYPOTHESIS
X.
THE STELLAR SYSTEM
The Open Page of the Heavens
Equatorial Constellations
Characteristics of the Stars
Number
Double and Multiple Stars
Colored Stars
Clusters of Stars
Nebulæ
Variable Stars
Temporary, New, and Lost Stars
Movements of Stars
XI.
THE WORLDS AND THE WORD
XII.
THE ULTIMATE FORCE
SUMMARY OF LATEST DISCOVERIES AND CONCLUSIONS
SOME ELEMENTS OF THE SOLAR SYSTEM
EXPLANATION OF ASTRONOMICAL SYMBOLS
Signs of the Zodiac
Other Abbreviations Used in the Almanac
Greek Alphabet Used Indicating the Stars
CHAUTAUQUA OUTLINE FOR STUDENTS
GLOSSARY OF ASTRONOMICAL TERMS AND INDEX
ILLUSTRATIONS
FIG.
The Constellations of Orion and Taurus
1.
An Orbit resulting from Attraction and Projection
2.
The Moon's Orbit about the Earth
3.
Changes of Orbit by Mutual Attraction
4.
Velocity of Light measured by Jupiter's Satellites
5.
Velocity of Light measured by Fizeau's Toothed Wheel
6.
White Light resolved into Colors
7.
Showing amount of Light received by Different Planets
8.
Measuring Intensities of Lights
9.
Reflection and Diffusion of Light
10.
Manifold Reflections
11.
Refraction by Water
12.
Atmospherical Reflection
13.
Refracting Telescope
14.
Reflecting Telescope
15.
The Cambridge Equatorial Refractor
16.
The new Reflecting Telescope at Paris
17.
Spectroscope, with Battery of Prisms
18.
Spectra of Glowing Hydrogen and of the Sun
19.
Illustrating Arcs and Angles
20.
Measuring Objects by observing Angles
21.
Mural Circle
22.
Scale to measure Hundredths of an Inch
23.
Spider-lines to determine Star Transits
24.
Illustrating Triangulation
25.
Measuring Distance to an Inaccessible Object
26.
Measuring Elevation of an Inaccessible Object
27.
Illustrating Parallax
28.
Illustrating Stellar Parallax
29.
Mode of Ascertaining Longitude
30.
Relative Size of Sun, as seen from Different Planets
31.
Zodiacal Light
32.
Corona of the Sun in 1858—Brazil
33.
Corona of the Sun in 1878—Colorado
34.
Solar Prominences of Flaming Hydrogen
35.
Changes in Solar Cavities during Rotation
36.
Solar Spot
37.
Holding Telescope to see the Sun-spots
38.
Orbits and Comparative Sizes of the Planets
39.
Orbit of Earth, illustrating Seasons
40.
Inclination of Planes of Planetary Orbits
41.
Inclination of Orbits of Earth and Venus
42.
Showing the Sun's Movement among the Stars
43.
Passage of the Sun by Star Regulus
44.
Apparent Path of Jupiter among the Stars
45.
Illustrating Position of Planets
46.
Apparent Movements of an Inferior Planet
47.
Apparent Movements of a Superior Planet
47
a
.
A Swarm of Meteors meeting the Earth
48.
Explosion of a Bolide
49.
Flight of Bolides
50.
The Santa Rosa Aerolite
51.
Orbit of November Meteors and the Comet of 1866
52.
Aspects of Remarkable Comets
53.
Phases and Apparent Dimensions of Venus
54.
The Earth and Moon in Space
55.
Aurora as Waving Curtains
56.
Tide resulting from Centrifugal Motion
57.
Lunar Landscape
58.
Telescopic View of the Moon
59.
Illumination of Lunar Craters and Peaks
60.
Lunar Crater "Copernicus"
61.
Eclipses: Shadows of Earth and Moon
62.
Apparent Sizes of Mars, seen from the Earth
63.
Jupiter
64.
Various Positions of Jupiter's Satellites
65.
View of Saturn and his Rings
66.
Perturbations of Uranus
67.
Map: Circumpolar Constellations
68.
Map of Constellations on the Meridian in December
69.
Map of Constellations on the Meridian in January
70.
Map of Constellations on the Meridian in April
71.
Map of Constellations on the Meridian in June
72.
Map of Constellations on the Meridian in September
73.
Map of Constellations on the Meridian in November
74.
Southern Circumpolar Constellations
75.
Aspects of Double Stars
76.
Sprayed Star Cluster below η in Hercules
77.
Globular Star Cluster in the Centaur
78.
Great Nebula about θ Orionis
79.
The Crab Nebula above ζ Tauri
80.
The Ring Nebula in Lyra
81.
Showing Place of Ring Nebula
82.
The Horizontal Pendulum
COLORED PLATE REPRESENTING VARIOUS SPECTA
MAPS TO FIND THE STARS
I.
CREATIVE PROCESSES.
"In the beginning God created the heaven and the earth. And the earth was without form, and void; and darkness was upon the face of the deep."—Genesis i. 1, 2.
"Not to the domes, where crumbling arch and column Attest the feebleness of mortal hand, But to that fane, most catholic and solemn, Which God hath planned,— To that cathedral, boundless as our wonder, Whose quenchless lamps the sun and stars supply; Its choir the winds and waves, its organ thunder, Its dome the sky." H. W. LONGFELLOW.
"The heavens are a point from the pen of His perfection; The world is a rose-bud from the bower of His beauty; The sun is a spark from the light of His wisdom; And the sky a bubble on the sea of His power." SIR W. JONES.
RECREATIONS IN ASTRONOMY.
I.
CREATIVE PROCESSES.
During all the ages there has been one bright and glittering page of loftiest wisdom unrolled before the eye of man. That this page may be read in every part, man's whole world turns him before it. This motion apparently changes the eternally stable stars into a moving panorama, but it is only so in appearance. The sky is a vast, immovable dial-plate of "that clock whose pendulum ticks ages instead of seconds," and whose time is eternity. The moon moves among the illuminated figures, traversing the dial quickly, like a second-hand, once a month. The sun, like a minute-hand, goes over the dial once a year. Various planets stand for hour-hands, moving over the dial in various periods reaching up to one hundred and sixty-four years; while the earth, like a ship of exploration, sails the infinite azure, bearing the observers to different points where they may investigate the infinite problems of this mighty machinery.
This dial not only shows present movements, but it keeps the history of uncounted ages past ready to be read backward in proper order; and it has glorious volumes of prophecy, revealing the far-off future to any man who is able to look thereon, break the seals, and read the record. Glowing stars are the alphabet of this lofty page. They combine to form words. Meteors, rainbows, auroras, shifting groups of stars, make pictures vast and significant as the armies, angels, and falling stars in the Revelation of St. John—changing and progressive pictures of infinite wisdom and power.
Men have not yet advanced as far as those who saw the pictures John describes, and hence the panorama is not understood. That continuous speech that day after day uttereth is not heard; the knowledge that night after night showeth is not seen; and the invisible things of God from the creation of the world, even his eternal power and Godhead, clearly discoverable from things that are made, are not apprehended.
The greatest triumphs of men's minds have been in astronomy—and ever must be. We have not learned its alphabet yet. We read only easy lessons, with as many mistakes as happy guesses. But in time we shall know all the letters, become familiar with the combinations, be apt at their interpretation, and will read with facility the lessons of wisdom and power that are written on the earth, blazoned in the skies, and pictured by the flowers below and the rainbows above.
In order to know how worlds move and develop, we must create them; we must go back to their beginning, give their endowment of forces, and study the laws of their unfolding. This we can easily do by that faculty wherein man is likest his Father, a creative imagination. God creates and embodies; we create, but it remains in thought only. But the creation is as bright, strong, clear, enduring, and real, as if it were embodied. Every one of us would make worlds enough to crush us, if we could embody as well as create. Our ambition would outrun our wisdom. Let us come into the high and ecstatic frame of mind which Shakspeare calls frenzy, in the exigencies of his verse, when
"The poet's eye, in a fine frenzy rolling, Doth glance from heaven to earth, from earth to heaven; And, as imagination bodies forth The forms of things unknown, the poet's pen Turns them to shapes, and gives to airy nothing A local habitation and a name."
In the supremacy of our creative imagination let us make empty space, in order that we may therein build up a new universe. Let us wave the wand of our power, so that all created things disappear. There is no world under our feet, no radiant clouds, no blazing sun, no silver moon, nor twinkling stars. We look up, there is no light; down, through immeasurable abysses, there is no form; all about, and there is no sound or sign of being—nothing save utter silence, utter darkness. It cannot be endured. Creation is a necessity of mind—even of the Divine mind.
We will now, by imagination, create a monster world, every atom of which shall be dowered with the single power of attraction. Every particle shall reach out its friendly hand, and there shall be a drawing together of every particle in existence. The laws governing this attraction shall be two. When these particles are associated together, the attraction shall be in proportion to the mass. A given mass will pull twice as much as one of half the size, because there is twice as much to pull. And a given mass will be pulled twice as much as one half as large, because there is twice as much to be pulled. A man who weighed one hundred and fifty pounds on the earth might weigh a ton and a half on a body as large as the sun. That shall be one law of attraction; and the other shall be that masses attract inversely as the square of distances between them. Absence shall affect friendships that have a material basis. If a body like the earth pulls a man one hundred and fifty pounds at the surface, or four thousand miles from the centre, it will pull the same man one-fourth as much at twice the distance, one-sixteenth as much at four times the distance. That is, he will weigh by a spring balance thirty-seven and a half pounds at eight thousand miles from the centre, and nine pounds six ounces at sixteen thousand miles from the centre, and he will weigh or be pulled by the earth 1/24 of a pound at the distance of the moon. But the moon would be large enough and near enough to pull twenty-four pounds on the same man, so the earth could not draw him away. Thus the two laws of attraction of gravitation are—1, Gravity is proportioned to the quantity of matter; and 2, The force of gravity varies inversely as the square of the distance from the centre of the attracting body.
The original form of matter is gas. Almost as I write comes the announcement that Mr. Lockyer has proved that all the so-called primary elements of matter are only so many different sized molecules of one original substance—hydrogen. Whether that is true or not, let us now create all the hydrogen we can imagine, either in differently sized masses or in combination with other substances. There it is! We cannot measure its bulk; we cannot fly around it in any recordable eons of time. It has boundaries, to be sure, for we are finite, but we cannot measure them. Let it alone, now; leave it to itself. What follows? It is dowered simply with attraction. The vast mass begins to shrink, the outer portions are drawn inward. They rush and swirl in vast cyclones, thousands of miles in extent. The centre grows compact, heat is evolved by impact, as will be explained in Chapter II. Dull red light begins to look like coming dawn. Centuries go by; contraction goes on; light blazes in insufferable brightness; tornadoes, whirlpools, and tempests scarcely signify anything as applied to such tumultuous tossing.
There hangs the only world in existence; it hangs in empty space. It has no tendency to rise; none to fall; none to move at all in any direction. It seethes and, flames, and holds itself together by attractive power, and that is all the force with which we have endowed it.
Leave it there alone, and withdraw millions of miles into space: it looks smaller and smaller. We lose sight of those distinctive spires of flame, those terrible movements. It only gives an even effulgence, a steady unflickering light. Turn one quarter round. Still we see our world, but it is at one side.
Now in front, in the utter darkness, suddenly create another world of the same size, and at the same distance from you. There they stand—two huge, lone bodies, in empty space. But we created them dowered with attraction. Each instantly feels the drawing influence of the other. They are mutually attractive, and begin to move toward each other. They hasten along an undeviating straight line. Their speed quickens at every mile. The attraction increases every moment. They fly swift as thought. They dash their flaming, seething foreheads together.
And now we have one world again. It is twice as large as before, that is all the difference. There is no variety, neither any motion; just simple flame, and nothing to be warmed thereby. Are our creative powers exhausted by this effort?
No, we will create another world, and add another power to it that shall keep them apart. That power shall be what is called the force of inertia, which is literally no power at all; it is an inability to originate or change motion. If a body is at rest, inertia is that quality by which it will forever remain so, unless acted upon by some force from without; and if a body is in motion, it will continue on at the same speed, in a straight line, forever, unless it is quickened, retarded, or turned from its path by some other force. Suppose our newly created sun is 860,000 miles in diameter. Go away 92,500,000 miles and create an earth eight thousand miles in diameter. It instantly feels the attractive power of the sun drawing it to itself sixty-eight miles a second. Now, just as it starts, give this earth a push in a line at right angles with line of fall to the sun, that shall send it one hundred and eighty-nine miles a second. It obeys both forces. The result is that the world moves constantly forward at the same speed by its inertia from that first push, and attraction momentarily draws it from its straight line, so that the new world circles round the other to the starting-point. Continuing under the operation of both forces, the worlds can never come together or fly apart.
They circle about each other as long as these forces endure; for the first world does not stand still and the second do all the going; both revolve around the centre of gravity common to both. In case the worlds are equal in mass, they will both take the same orbit around a central stationary point, midway between the two. In case their mass be as one to eighty-one, as in the case of the earth and the moon, the centre of gravity around which both turn will be 1/81 of the distance from the earth's centre to the moon's centre. This brings the central point around which both worlds swing just inside the surface of the earth. It is like an apple attached by a string, and swung around the hand; the hand moves a little, the apple very much.
Thus the problem of two revolving bodies is readily comprehended. The two bodies lie in easy beds, and swing obedient to constant forces. When another body, however, is introduced, with its varying attraction, first on one and then on the other, complications are introduced that only the most masterly minds can follow. Introduce a dozen or a million bodies, and complications arise that only Omniscience can unravel.
Let the hand swing an apple by an elastic cord. When the apple falls toward the earth it feels another force besides that derived from the hand, which greatly lengthens the elastic cord. To tear it away from the earth's attraction, and make it rise, requires additional force, and hence the string is lengthened; but when it passes over the hand the earth attracts it downward, and the string is very much shortened: so the moon, held by an elastic cord, swings around the earth. From its extreme distance from the earth, at A, Fig. 2, it rushes with increasing speed nearly a quarter of a Fig. 2. million of miles toward the sun, feeling its attraction increase with every mile until it reaches B; then it is retarded in its speed, by the same attraction, as it climbs back its quarter of a million of miles away from the sun, in defiance of its power, to C. All the while the invisible elastic force of the earth is unweariedly maintained; and though the moon's distances vary over a range of 31,355 miles, the moon is always in a determinable place. A simple revolution of one world about another in a circular orbit would be a problem of easy solution. It would always be at the same distance from its centre, and going with the same velocity. But there are over sixty causes that interfere with such a simple orbit in the case of the moon, all of which causes and their disturbances must be considered in calculating such a simple matter as an eclipse, or predicting the moon's place as the sailors guide. One of the most puzzling of the irregularities of our night-wandering orb has just been explained by Professor Hansen, of Gotha, as a curious result of the attraction of Venus.
Take a single instance of the perturbations of Jupiter and Saturn which can be rendered evident. The times of orbital revolution of Saturn and Jupiter are nearly as five to two. Suppose the orbits of Fig. 3.—Changes of orbit by mutual attraction. the planets to be, as in Fig. 3, both ellipses, but not necessarily equally distant in all parts. The planets are as near as possible at 1, 1. Drawn toward each other by mutual attraction, Jupiter's orbit bends outward, and Saturn's becomes more nearly straight, as shown by the dotted lines. A partial correction of this difficulty immediately follows. As Jupiter moves on ahead of Saturn it is held back—retarded in its orbit by that body; and Saturn is hastened in its orbit by the attraction of Jupiter. Now greater speed means a straighter orbit. A rifle-ball flies nearer in a straight line than a thrown stone. A greater velocity given to a whirled ball pulls the elastic cord far enough to give the ball a larger orbit. Hence, being hastened, Saturn stretches out nearer its proper orbit, and, retarded, Jupiter approaches the smaller curve that is its true orbit.
But if they were always to meet at this point, as they would if Jupiter made two revolutions to Saturn's one, it would be disastrous. In reality, when Saturn has gone around two-thirds of its orbit to 2, Jupiter will have gone once and two-thirds around and overtaken Saturn; and they will be near again, be drawn together, hastened, and retarded, as before; their next conjunction would be at 3, 3, etc.
Now, if they always made their conjunction at points equally distant, or at thirds of their orbits, it would cause a series of increasing deviations; for Jupiter would be constantly swelling his orbit at three points, and Saturn increasingly contracting his orbit at the same points. Disaster would be easily foretold. But as their times of orbital revolutions are not exactly in the ratio of five and two, their points of conjunction slowly travel around the orbit, till, in a period of nine hundred years, the starting-point is again reached, and the perturbations have mutually corrected one another.
For example, the total attractive effect of one planet on the other for 450 years is to quicken its speed. The effect for the next 450 years is to retard. The place of Saturn, when all the retardations have accumulated for 450 years, is one degree behind what it is computed if they are not considered; and 450 years later it will be one degree before its computed place—a perturbation of two degrees. When a bullet is a little heavier or ragged on one side, it will constantly swerve in that direction. The spiral groove in the rifle, of one turn in forty-five feet, turns the disturbing weight or raggedness from side to side—makes one error correct another, and so the ball flies straight to the bull's-eye. So the place of Jupiter and Saturn, though further complicated by four moons in the case of Jupiter, and eight in the case of Saturn, and also by perturbations caused by other planets, can be calculated with exceeding nicety.
The difficulties would be greatly increased if the orbits of Saturn and Jupiter, instead of being 400,000,000 miles apart, were interlaced. Yet there are the orbits of one hundred and ninety-two asteroids so interlaced that, if they were made of wire, no one could be lifted without raising the whole net-work of them. Nevertheless, all these swift chariots of the sky race along the course of their intermingling tracks as securely as if they were each guided by an intelligent mind. They are guided by an intelligent mind and an almighty arm.
Still more complicated is the question of the mutual attractions of all the planets. Lagrange has been able to show, by a mathematical genius that seems little short of omniscience in his single department of knowledge, that there is a discovered system of oscillations, affecting the entire planetary system, the periods of which are immensely long. The number of these oscillations is equal to that of all the planets, and their periods range from 50,000 to 2,000,000 years,
Looking into the open page of the starry heavens we see double stars, the constituent parts of which must revolve around a centre common to them both, or rush to a common ruin. Eagerly we look to see if they revolve, and beholding them in the very act, we conclude, not groundlessly, that the same great law of gravitation holds good in distant stellar spaces, and that there the same sufficient mind plans, and the same sufficient power directs and controls all movements in harmony and security.
When we come to the perturbations caused by the mutual attractions of the sun, nine planets, twenty moons, one hundred and ninety-two asteroids, millions of comets, and innumerable meteoric bodies swarming in space, and when we add to all these, that belong to one solar system, the attractions of all the systems of the other suns that sparkle on a brilliant winter night, we are compelled to say, "As high as the heavens are above the earth, so high above our thoughts and ways must be the thoughts and ways of Him who comprehends and directs them all."
II.
CREATIVE PROGRESS.
"And God said, Let there be light, and there was light."—Genesis i., 3.
"God is light."—1 John, i. 5.
"Hail! holy light, offspring of Heaven first born, Or of the eternal, co-eternal beam, May I express thee unblamed? since God is light, And never but in unapproached light Dwelt from eternity, dwelt then in thee, Bright effluence of bright essence increate." MILTON.
"A million torches lighted by Thy hand Wander unwearied through the blue abyss: They own Thy power, accomplish Thy command, All gay with life, all eloquent with bliss. What shall we call them? Piles of crystal light— A glorious company of golden streams— Lamps of celestial ether burning bright— Suns lighting systems with their joyous beams? But 'Thou to these art as the noon to night." DERZHAVIN, trans. by BOWRING.
II.
CREATIVE PROGRESS.
Worlds would be very imperfect and useless when simply endowed with attraction and inertia, if no time were allowed for these forces to work out their legitimate results. We want something more than swirling seas of attracted gases, something more than compacted rocks. We look for soil, verdure, a paradise of beauty, animal life, and immortal minds. Let us go on with the process.
Light is the child of force, and the child, like its father, is full of power. We dowered our created world with but a single quality—a force of attraction. It not only had attraction for its own material substance, but sent out an all-pervasive attraction into space. By the force of condensation it flamed like a sun, and not only lighted its own substance, but it filled all space with the luminous outgoings of its power. A world may be limited, but its influence cannot; its body may have bounds, but its soul is infinite. Everywhere is its manifestation as real, power as effective, presence as actual, as at the central point. He that studies ponderable bodies alone is not studying the universe, only its skeleton. Skeletons are somewhat interesting in themselves, but far more so when covered with flesh, flushed with beauty, and inspired with soul. The universe has bones, flesh, beauty, soul, and all is one. It can be understood only by a study of all its parts, and by tracing effect to cause.
But how can condensation cause light? Power cannot be quiet. The mighty locomotive trembles with its own energy. A smitten piece of iron has all its infinitesimal atoms set in vehement commotion; they surge back and forth among themselves, like the waves of a storm-blown lake. Heat is a mode of motion. A heated body commences a vigorous vibration among its particles, and communicates these vibrations to the surrounding air and ether. When these vibrations reach 396,000,000,000,000 per second, the human eye, fitted to be affected by that number, discerns the emitted undulations, and the object seems to glow with a dull red light; becoming hotter, the vibrations increase in rapidity. When they reach 765,000,000,000,000 per second the color becomes violet, and the eye can observe them no farther. Between these numbers are those of different rapidities, which affect the eye—as orange, yellow, green, blue, indigo, in an almost infinite number of shades—according to the sensitiveness of the eye.
We now see how our dark immensity of attractive atoms can become luminous. A force of compression results in vibrations within, communicated to the ether, discerned by the eye. Illustrations are numerous. If we suddenly push a piston into a cylinder of brass, the force produces heat enough to set fire to an inflammable substance within. Strike a half-inch cube of iron a moderate blow and it becomes warm; a sufficient blow, and its vibrations become quick enough to be seen—it is red-hot. Attach a thermometer to an extended arm of a whirling wheel; drive it against the air five hundred feet per second, the mercury rises 16°. The earth goes 98,000 feet per second, or one thousand miles a minute. If it come to an aerolite or mass of metallic rock, or even a cloudlet of gas, standing still in space, its contact with our air evolves 600,000° of heat. And when the meteor comes toward the world twenty-six miles a second, the heat would become proportionally greater if the meteor could abide it, and not be consumed in fervent heat. It vanishes almost as soon as seen. If there were meteoric masses enough lying in our path, our sky would blaze with myriads of flashes of light. Enough have been seen to enable a person to read by them at night. If a sufficient number were present, we should miss their individual flashes as they blend their separate fires in one sea of insufferable glory. The sun is 1,300,000 times as large as our planet; its attraction proportionally greater; the aerolites more numerous; and hence an infinite hail of stones, small masses and little worlds, makes ceaseless trails of light, whose individuality is lost in one dazzling sea of glory.
On the 1st day of September, 1859, two astronomers, independently of each other, saw a sudden brightening on the surface of the sun. Probably two large meteoric masses were travelling side by side at two or three hundred miles per second, and striking the sun's atmosphere, suddenly blazed into light bright enough to be seen on the intolerable light of the photosphere as a background. The earth responded to this new cause of brilliance and heat in the sun. Vivid auroras appeared, not only at the north and south poles, but even where such spectacles are seldom seen. The electro-magnetic disturbances were more distinctly marked. "In many places the telegraphic wires struck work. In Washington and Philadelphia the electric signalmen received severe electric shocks; at a station in Norway the telegraphic apparatus was set fire to; and at Boston a flame of fire followed the pen of Bain's electric telegraph." There is the best of reason for believing that a continuous succession of such bodies might have gone far toward rendering the earth uncomfortable as a place of residence.
Of course, the same result of heat and light would follow from compression, if a body had the power of contraction in itself. We endowed every particle of our gas, myriads of miles in extent, with an attraction for every other particle. It immediately compressed itself into a light-giving body, which flamed out through the interstellar spaces, flushing all the celestial regions with exuberant light.
But heat exerts a repellent force among particles, and soon an equilibrium is reached, for there comes a time when the contracting body can contract no farther. But heat and light radiate away into cold space, then contraction goes on evolving more light, and so the suns flame on through the millions of years unquenched. It is estimated that the contraction of our sun, from filling immensity of space to its present size, could not afford heat enough to last more than 18,000,000 years, and that its contraction from its present density (that of a swamp) to such rock as that of which our earth is composed, could supply heat enough for 17,000,000 years longer. But the far-seeing mind of man knows a time must come when the present force of attraction shall have produced all the heat it can, and a new force of attraction must be added, or the sun itself will become cold as a cinder, dead as a burned-out char.
Since light and heat are the product of such enormous cosmic forces, they must partake of their nature, and be force. So they are. The sun has long arms, and they are full of unconquerable strength ninety-two millions, or any other number of millions, of miles away. All this light and heat comes through space that is 200° below zero, through utter darkness, and appears only on the earth. So the gas is darkness in the underground pipes, but light at the burner. So the electric power is unfelt by the cable in the bosom of the deep, but is expressive of thought and feeling at the end. Having found the cause of light, we will commence a study of its qualities and powers.
Light is the astronomer's necessity. When the sublime word was uttered, "Let there be light!" the study of astronomy was made possible. Man can gather but little of it with his eye; so he takes a lens twenty-six inches in diameter, and bends all the light that passes through it to a focus, then magnifies the image and takes it into his eye. Or he takes a mirror, six feet in diameter, so hollowed in the middle as to reflect all the rays falling upon it to one point, and makes this larger eye fill his own with light. By this larger light-gathering he discerns things for which the light falling on his pupil one-fifth of an inch in diameter would not be sufficient. We never have seen any sun or stars; we have only seen the light that left them fifty minutes or years ago, more or less. Light is the aërial sprite that carries our measuring-rods across the infinite spaces; light spreads out the history of that far-off beginning; brings us the measure of stars a thousand times brighter than our sun; takes up into itself evidences of the very constitutional elements of the far-off suns, and spreads them at our feet. It is of such capacity that the Divine nature, looking for an expression of its own omnipotence, omniscience, and power of revelation, was content to say, "God is Light." We shall need all our delicacy of analysis and measurement when we seek to determine the activities of matter so fine and near to spirit as light.
We first seek the velocity of light. In Fig. 4 the earth is 92,500,000 miles from the sun at E; Jupiter is 480,000,000 miles from the sun at J. It has four moons: the inner one goes around the central body in forty-two hours, and is eclipsed at every revolution. The light that went out from the sun to M ceases to be reflected back to the earth by the intervention of the planet Jupiter. We know to a second when these eclipses take place, and they can be seen with a small telescope. But when the earth is on the opposite side of the sun from Jupiter, at E', these eclipses at J' take place sixteen and a half minutes too late. What is the reason? Is the celestial chronometry getting deranged? No, indeed; these great worlds swing never an inch out of place, nor a second out of time. By going to the other side of the sun the earth is 184,000,000 miles farther from Jupiter, and the light that brings the intelligence of that eclipse consumes the extra time in going over the extra distance. Divide one by the other and we get the velocity, 185,000 miles Fig. 5.—Measuring the Velocity of Light. per second. That is probably correct to within a thousand miles. Methods of measurement by the toothed wheel of Fizeau confirm this result. Suppose the wheel, Fig. 5, to have one thousand teeth, making five revolutions to the second. Five thousand flashes of light each second will dart out. Let each flash travel nine miles to a mirror and return. If it goes that distance in 1/10000 of a second, or at the rate of 180,000 miles a second, the next tooth will have arrived before the eye, and each returning ray be cut off. Hasten the revolutions a little, and the next notch will then admit the ray, on its return, that went out of each previous notch: the eighteen miles having been traversed meanwhile. The method of measuring by means of a revolving mirror, used by Faucault, is held to be even more accurate.
When we take instantaneous photographs by the exposure of the sensitive plate 1/20000 part of a second, a stream of light nine miles long dashes in upon the plate in that very brief period of time.
The highest velocity we can give a rifle-ball is 2000 feet a second, the next second it is only 1500 feet, and soon it comes to rest. We cannot compact force enough behind a bit of lead to keep it flying. But light flies unweariedly and without diminution of speed. When it has come from the sun in eight minutes, Alpha Centauri in three years, Polaris in forty-five years, other stars in one thousand, its wings are in nowise fatigued, nor is the rapidity of its flight slackened in the least.
It is not the transactions of to-day that we read in the heavens, but it is history, some of it older than the time of Adam. Those stars may have been smitten out of existence decades of centuries ago, but their poured-out light is yet flooding the heavens.
It goes both ways at once in the same place, without interference. We see the light reflected from the new moon to the earth; reflected back from the house-tops, fields, and waters of earth, to the moon again, and from the moon to us once more—three times in opposite directions, in the same place, without interference, and thus we see "the old moon in the arms of the new."
Constitution of Light.
Light was once supposed to be corpuscular, or consisting of transmitted particles. It is now known to be the result of undulations in ether. Reference has been made to the minuteness of these undulations. Their velocity is equally wonderful. Put a prism of glass into a ray of light coming into a dark room, and it is instantly turned out of its course, some parts more and some less, according to the number of vibrations, and appears as the seven colors on different parts of the screen. Fig. 6 shows the arrangement of colors, and the number of millions of millions of vibrations per second of each. But the different divisions we call colors are Fig. 6.—White Light resolved into Colors.
