GIFT OF
AUVHOR
o4
d
HOW TO KNOW THE STARRY
HEAVENS
^. .
FIG. 1. SOLAK PROMINENCES, BY TROUVELOT, OF HARVARD
OBSERVATORY
The white circle represents the size of the Earth on the same scale.
HOW TO KNOW
THE
STARRY HEAVENS
AN INVITATION TO THE
STUDY OF SUNS AND WORLDS
BY
EDWARD IRVING
WITH CHARTS, COLOURED PLATES, DIAGRAMS,
AND MANY ENGRAVINGS OF
PHOTOGRAPHS
NEW YORK
FREDERICK A. STOKES COMPANY
PUBLISHERS
COPYRIGHT, 1904
BY FREDERICK A. STOKES COMPANY
All rights reserved
Published in November, 1904
THE UNIVERSITY PRESS, CAMBRIDGE, U. S. A.
"Everybody should study astronomy. It is the most delightful
of all the sciences. It is the most inspiring of all. It lifts and
broadens the mind. It rouses the imagination, and the imagination
is the most God-like of human faculties, because it is the most
creative. Let no one be deterred by the superstition that it is
necessary to be a mathematician in order to understand and enjoy
astronomy. You can let the mathematics of the subject severely
alone and yet Jind inexhaustible pleasure and advantage in astro-
nomical study. It is because they were compelled to begin at the
mathematical end of the subject that hundreds of thousands of
graduates from schools and colleges have virtually no knowledge of
astronomy. Mathematical gifts are rare, but they are not essential
to the enjoyment of astronomy." GARRETT P. SERVISS.
PREFACE
THIS volume is not so much a text-book on Astronomy, as
an invitation to read text-books on that subject. In other
words, it is a careful selection of the most typical, interesting,
and instructive facts and theories concerning the Universe
around us. The author has endeavoured to describe and illus-
trate these in such a way as to attract, interest, and inform the
general reader. But, though intended primarily for beginners,
every effort has been made to avoid offending those who are
further advanced, by sensationalism or a want of proportion and
accuracy. The comparisons and illustrations used are the re-
sult of many years' study, and have been successfully used in
lectures and classes. They may interest some who are well
acquainted with the facts of astronomy, but have not looked at
them from the same standpoint.
Many interesting and important astronomical methods, prin-
ciples, and facts have been left out of this volume, to avoid
overcrowding and confusion. The main object of the work is
not so much to describe individual worlds, as to enable the
reader to realise, as far as possible, what the Universe itself is
like. In other words, it is to give a bird's-eye view of the
celestial forest from a general and philosophical standpoint,
so that the individual trees may be afterwards examined more
at leisure. Until such a bird's-eye view has been obtained, the
learner is apt to be confused by the details. As the old saying
has it, he " cannot see the wood for the trees."
When such a general view has once been obtained, the details
no longer confuse, and text-books that were formerly thrown
down in disgust become luminous with the ever-growing interest
that rightly belongs to the physical sciences.
viii PREFACE
The figures given in this work are mostly round numbers.
They do not claim absolute accuracy, but at the same time
every effort has been made to avoid serious errors.
The distance of the nearest star has been given as about
9,000 times as great as that of Neptune. It is quite possible
that further investigations may result in other figures being
adopted. But even if it should be changed to 8,000 or 10,000,
the comparisons used will still serve to illustrate the relative
dimensions of the visible Universe.
The author gratefully acknowledges the kindness of Professor
K. G. Aitken and other members of the staff at the Lick Ob-
servatory, in reading the manuscript and making suggestions
which have materially helped to perfect the work.
Thanks are due to many who have given advice, suggestions,
corrections, and information; also to those who have granted
the reproduction of valuable photographs and drawings. Among
these are :
The late Dr. E. Keeler, Director of Lick Observatory,
California.
Dr. W. W. Campbell, Director of Lick Observatory, California.
Dr. A. 0. Leuschner, Director of Students' Observatory,
Berkeley, Cal.
E. L. Larkin, Director of Lowe Observatory, California.
C. Burckhalter, Director of Chabot Observatory, Oakland, Cal.
G. E. Hale, Director of Yerkes Observatory, Wisconsin.
E. C. Pickering, Director of Harvard Observatory, Massa-
chusetts.
W. H. M. Christie, M.A., Astronomer Eoyal, Greenwich,
England.
E. Walter Maunder, F.K.A.S., Greenwich, England.
Besides giving an account of well-known and indisputable
astronomical facts, the author has touched upon certain specu-
lative theories which cannot yet be proved by either experiment
or observation. The most that can be said for them is that
they give a reasonable explanation of a large number of ob-
served phenomena, and must therefore contain a certain amount
PREFACE ix
of truth. They also help to give us a better idea of the Infinite
and Eternal Drama in which our little Earth is playing its
obscure and ephemeral part. The reader is not asked to accept
these theories if he can explain the observed phenomena by
more probable speculations of his own. But he must beware
of adopting theories which conflict largely with ascertained
facts.
It only remains to be said that these speculations have
everywhere been carefully distinguished from those facts which
are so well proved as to be practically indisputable.
This volume is intended to be the first of a series, by the
same writer, dealing with the sciences of astronomy, geology,
biology, and sociology. These four were grouped together by
the late Herbert Spencer under the name of the Concrete
Sciences. Though the vast importance of these subjects is
now generally recognised, many otherwise educated people are
lamentably deficient in them. This is very unfortunate for the
individuals concerned, for, however learned a man may be in
all other subjects, it is impossible for him to be truly broad-
minded, philosophical, and cosmopolitan, without some knowl-
edge of these Concrete Sciences. 1
A general lack of scientific knowledge injures, not only the
individuals themselves, but also society at large. In spite of
the great advances made in all directions during the last century,
there are still many imperfections remaining in our systems of
government, of administrative justice, of national education, and
in our entire social and moral organisations. These imperfec-
tions are largely due to the fact that many of our statesmen,
lawyers, teachers, doctors, and preachers are deficient in the
above-mentioned sciences. Let us hope that during the present
1 As the philosophical A. Zazel truly says :
" Astronomy, geology, biology, and sociology together form an impregnable
bulwark against the inroads of superstition. And where the seeds of that deadly
mental disease have been already sown, these sciences form an infallible antidote
and cure."
x PREFACE
century this ignorance may be removed, so that our upward
progress may no longer be impeded by the erroneous ideas that
have been dragged up with us from the flat world in which our
ancestors imagined themselves to be living.
The second volume will deal with the history of the Third
Planet in our System, from its nebulous birth to the advent of
Man. Its title will probably be How to Know the Earth's
History.
EDWARD IRVING.
BERKELEY, CAL. (U. S.),
October, 1904.
CONTENTS
CHAPTER P AGK
I. APPARENT MOTIONS OF THE HEAVENLY BODIES AS
SHOWN BY OBSERVATION 1
II. RIVAL THEORIES TO EXPLAIN THE APPARENT MOTIONS
OF THE HEAVENLY BODIES 15
III. PRINCIPLES UTILISED FOR MEASURING THE UNIVERSE 26
IV. SOME PROBLEMS USED IN CELESTIAL MEASUREMENTS 39
V. THE CHARIOT OF IMAGINATION 53
VI. DIMENSIONS OF THE UNIVERSE ......... 68
VII. SOME MORE DIMENSIONS 77
VIII. THE PRINCIPLES AND APPLICATIONS OF THE SPECTRO-
SCOPE 87
IX. A STAR-SPANGLED BANNER 102
X. CONSTRUCTION OF THE UNIVERSE 114
XL SOLAR ARCHITECTURE 125
XII. A REELING WORLD 136
XIII. KEPLER'S THREE LAWS 155
XIV. GALILEO'S LAWS OF MOTION 163
XV. NEWTON'S LAW OF GRAVITATION 167
XVI. ANCIENT COSMOGONIES, AND THE NEBULAR HYPOTHESIS 178
XVII. THEORIES AND DISCOVERIES MODIFYING THE NEBULAR
HYPOTHESIS 190
XVIII. MODIFICATIONS OF THE NEBULAR THEORY .... 205
XIX. THE MESSENGERS OF HEAVEN 219
XX. LARGE AND SMALL WORLDS 233
x COiNTENTS
CHAPTER PAGE
XXI. IGNEOUS FORCES ON THE MOON AND ELSEWHERE . . 243
XXII. LUNAR GEOLOGY AND GEOGRAPHY 257
XXIII. INHABITED WORLDS 265
XXIV. SIZE, IMPORTANCE, SPEED, AND DURATION .... 283
XXV. CONCLUSION 290
APPENDIX A. FACTS AND FANCIES CONCERNING MATTER . . 295
APPENDIX B. THE GREEK ALPHABET 301
APPENDIX C. THE LUNAR CRATERS 302
INDEX . , 309
ILLUSTRATIONS
FULL-PAGE ILLUSTRATIONS
FIGURE
1. Solar Prominences, by Trouvelot, of Harvard Observatory
frontispiece in colours
FACING PAGK
7. Northern Star-Trails 14
8. The Dipper, or Great Bear, at Intervals of Six Hours ... 14
24. Sun, Showing Spots and Faculse 52
25. Group of Sunspots 58
26. Solar Flames and Corona, as Seen During Eclipse of May 28,
1900. (In colours) 56
27. Eruptive Prominences 58
28. Solar Corona. Eclipse of May 28, 1900 60
29. North Polar Streamers of the Corona. May 28, 1900 ... 60
30. Mercury, the First Planet 62
31. Venus, the Second Planet 62
33. Mars, the Fourth Planet 62
35. The Zone of Asteroids Between Mars and Jupiter .... 64
36. Jupiter, the Largest Planet 64
38. Saturn, the Ringed Planet 66
41. Lick Observatory on Mount Hamilton, California 70
42. Main Entrance and Great Dome, Lick Observatory .... 70
43. The Thirty-Six-Inch Refractor at Lick Observatory . . . 72
44. Eye-Piece of the Great Lick Telescope 74
45. Yerkes Observatory, Williams Bay, Wisconsin 80
46. The Forty-Inch Refractor of the Yerkes Observatory: tin-
Largest in the World 80
47. Milky Way Surrounding Messier II
48. The Star-Cluster Messier II 84
53. Laboratory and Celestial Spectra. (In colours) 94
54. Tele-Spectroscope
55. The Mills Spectrograph at Lick Observatory 96
56. Chief Lines in the Solar Spectrum (Herschel) .
57. Part of the Spectra of Four Red Stars (Hale and Ellerinan) . 100
58. Star Spectra Showing Displacement of Lines Due to Star's
Motion in Line of Sight
xiv ILLUSTRATIONS
FIOUBE FACING PAGE
59. Coloured Double Stars. (In colours) 108
60. Star-Cluster in Hercules 112
61. Part of the Milky Way in Sagittarius 114
62. A Rope-like Nebula in Cygnus 114
63. Spiral Nebula in Triangulum 116
64. The Great Nebula in Andromeda 118
65. A Spiral Nebula Seen Edgeways 120
66. The Ring Nebula in Lyra 120
67. The Trifid Nebula in Sagittarius -122
68. Great Nebula in Orion 124
69. A Typical Sunspot 128
70. Solar " Flames " or Prominences 132
75. The Solar Corona During the Eclipse of July 29, 1878 ... 134
76. Theoretical Section of Solar Photosphere 132
79. Equatorial Mounting of the Crossley Reflector, Lick Observatory 150
80. Meridian Circle 150
82. Drawing an Ellipse 158
84. Mount Lowe Observatory, in Southern California 168
85. Spiral Nebula in Ursa Major (M 81) 172
91. Dumb-Bell Nebula 192
92. Nova Persei, 1901. Showing Movement of Surrounding Nebu-
losity. Lick Photographs " 196
93. Spectra of Nova Persei, Showing Changes 200
94. The Star- Cluster Omega Centauri 204
100. A Celestial Messenger Approaching a Star 222
101. Brook's Comet, 1893 222
102. Comet 1903 C 222
106. Donati's Comet, 1858 228
107. Comet Rordame, 1893 228
109. The California Meteor of July 27, 1894 232
113. Full Moon, Showing Radiating Streaks 244
114. The Moon, at First and Last Quarter 248
117. Clavius and Tycho 252
118. Theophilus, a Lunar Crater-With-Cone 254
122. Mare Crisium, a Lunar Plain 258
123. Lunar Apennines and Alps 258
124. Copernicus 260
125. Schickard and Wargentin 262
126. Ptolemy, Alphons, and Arzachel 264
127. Twelve Views of Mars . 268
128. Disc of the Sun, August 12, 1903 274
ILLUSTRATIONS xv
CHARTS
Chart A. The Northern Heavens | PACING PAGE
Key to Chart A. (In colours) J 282
Chart B. The Equatorial Constellations. For Spring Evenings ]
Key to Chart B. (In colours) . j -290
Chart C. The Equatorial Constellations. For Summer Evenings )
Key to Chart C. (In colours) . } 294
Chart D. The Equatorial Constellations. For Winter Evenings )
Key to Chart D. (In colours) } 30
Chart E. Eastern Half of Moon. (In colours) )
Chart F. Western Half of Moon. (In colours) \ 804
Chart G. The Constellation Figures 308
ILLUSTRATIONS IN THE TEXT
FIGURE p AG s
2. Umbrella-Apparatus for Illustrating (Apparent) Star Move-
ments 5
3. The Earth, Showing Relative Positions of Apparatus when Used
at Equator, Poles, etc 7
4. Umbrella- Apparatus Modified for Illustrating Apparent Move-
ments of Sun and Planets 8
5. Circles of the Celestial Sphere with World in the Centre . . 9
6. An Adjustable Equatorial, Suitable for any Part of the World 13
9. The Ptolemaic System 19
10. The Tychonic System 20
11. Copernican System 23
12. Relative Positions of Earth and Sun at the four Seasons ... 24
13. Orbits of Mercury, Venus, and Earth 28
14. Estimating Distances with the Eyes 31
15. Surveying from a Base-line 32
16. Daily Positions of Earth and Moon ....*.... 37
1 7. Arc of Circle 40
18. Chord of Arc . 41
19. Sine of Angle 42
20. Measuring Width of River 43
21. Measuring Distance of Moon 46
22. Arc of Circle 47
23. Sine of Angle 50
32. Terra, the Third Planet, and Its Satellite or Moon .... 63
34. Relative Sizes of Earth and Mars 64
37. Relative Sizes of Jupiter and Earth 65
xvi ILLUSTRATIONS
FIGURE PAGE
39. Relative Sizes of Saturn and Earth 66
40. Relative Sizes of Neptune and Earth 67
49. A Prism and its Spectrum 90
50. A One-prism Spectroscope 91
51. Section of a One-prism Spectroscope 92
52. A Compound Spectroscope 93
71. A Solar " Cloud " of Glowing Hydrogen (Professor Young) . . 131
72. The Same Region 35 Minutes Later (Young) 132
73. The Same Region 35 Minutes Later (Young) 133
74. The Same, 15 Minutes Later (Young) 133
77. Diagram Illustrating Zodiac 137
78. Diagram Illustrating Precession of Equinoxes and Advance of
Perihelion 143
81. Alt- Azimuth Mounting for Small Telescope 153
83. An Elliptical Orbit, Divided into Twelve Monthly Parts . . . 159
86. Original Nebula, after its Rotation has Produced a Disc-like
Form 184
87. Nebula with Outer Ring, left behind by Contraction and Conse-
quent Quickening of Rotation 185
88. Central Condensation Surrounded by Rings 186
89. Rings Collapsing into Planets, and Central Condensation Turn-
ing to a Luminous Sun 187
90. Solar System as it is now 188
95. Earth-tides, if the Day and Month Were Equal 213
96. Acceleration of Moon by Forward Pull of Earth-tide . . . . 214
97. Loop in Apparent Path of Mars 215
98. Diagram Showing Cause of Loop in Apparent Path of Mars . 216
99. A Celestial Messenger on a Journey 221
103. Parabolic Orbit of a Free Comet 227
104. Elliptical Orbits of Captive Comets 228
105. Tail of a Comet near Perihelion 229
108. A Meteor Bursting in the Atmosphere 230
110. Relative Sizes of Planets 234
111. Relative Sizes of Sun, Jupiter, and Earth 235
112. Relative Sizes of the First Four Asteroids and the Earth's Satel-
lite 236
115. Section of Earthly Volcanoes 251
116. Section of Lunar Volcano in full Activity 252
119. Section of Mountain of Exudation 254
1 20. Section of Mountain of Elevation 254
121. Section of Lunar Crater with Cone 255
HOW TO KNOW THE
STARRY HEAVENS
CHAPTER-
APPARENT MOTIONS OF THE HEAVENLY BODIES AS
SHOWN BY OBSERVATION
" Appearances are deceptive." Old Saying.
"Ne jugez pas selon 1'apparence, raais jugez selon la justice."
Fourth Gospel, vii, 24 (Segond).
" Things are not what they seem." Longfellow.
SUPERFICIAL APPEARANCES
BEFORE describing the Universe as it is, I wish to say a
few words about the Universe as it seems. We shall then
be better able to judge as to the reasonableness, or otherwise,
of the various theories which have from time to time been
brought forward to explain the celestial phenomena which are
going on around us. It may be well also, before dealing with
the dimensions of the Universe, to give a very brief account
of the methods used by astronomers to enable them to ascer-
tain the distances and dimensions of those celestial bodies
which are within a measurable distance of our World.
The conclusions at which modern astronomy has arrived are
not those which would naturally occur to the first observers of
the heavenly bodies. The conditions, indeed, are such that
superficial observations always lead to wrong conclusions. To-
day, in most of our so-called civilised countries, the people in
general take it for granted that the Earth is a planet going around
the Sun. Many of them have also heard that the stars are far-off
suns, floating in practically empty space. Yet not one person
l
2 HOW TO KNOW THE STARRY HEAVENS
in a thousand truly realises what these statements mean. They
are merely hearsay, accepted in childlike faith, as some of the
ancients accepted the statement that the Earth is supported by
a number of elephants standing on the back of a big turtle
whose legs reach all the way down !
Bu.t in those Countries where the secular schools have not
familiarised the people' with the accepted teachings of modern
astra'nc!ray,.a man who asserts to-day that the Earth goes around
the Sun is regarded as either a wag or a lunatic. If people
condescend to argue the point with him, they can overwhelm
him with apparently good reasons for their incredulity. They
can not only give plausible arguments from their own surround-
ings and experiences, but can also prove their case by wholesale
quotations from the writings of the " inspired " priests and
prophets of former times. If he suggests that their surround-
ings and experiences are wrongly interpreted, they laugh him
to scorn. If he insists that the ancient writers were ignorant
and mistaken, they abuse him as an infidel. If, to avoid their
resentment, he tells them that the writers of their sacred books
did not intend that their statements should be understood
literally, they truly and philosophically reply that he is wrest-
ing the Scriptures to his own destruction.
ONLY FACTS WANTED
Seekers after truth should not be satisfied with mere hear-
say. Those who expect to get facts by faith alone generally
accumulate fables instead of facts. Where faith is relied on, it
is a mere matter of where we are born as to what we believe.
Faith may possibly do no harm as regards immaterial or child-
ish beliefs, but it is very hurtful when used for material or
important matters, which require intelligent scepticism to enable
us to sort out the true from the false.
Even if by accident we should get the Truth by faith alone,
it would do us no good. One of the founders of Christianity
told his followers to "prove all things" and " hold fast that
which is good " (I Thess. v, 21). A better precept was never
APPARENT MOTIONS OF HEAVENLY BODIES 3
given, though many who profess to walk in his footsteps do not
seem very enthusiastic about following his counsel.
Those who are looking for actual facts concerning the Uni-
verse should therefore leave faith to those who are satisfied
with pleasant fables and flattering delusions. They should
endeavour, by all the means at their command, to ascertain for
themselves whether these things are truly as represented, and
they should also try to realise what the facts of the case really
involve.
THE MUSIC OF THE SPHERES
As regards the shape of our Earth, it is not now necessary to
prove that it is a sphere. Many of us have travelled enough
to satisfy ourselves by actual experience as to its general size
and shape. Even those who have lived all their lives in one
locality have now plenty of positive evidence that the old
theory of its being flat is untenable. As regards the rest of the
Universe, however, we still have to rely on observation and
abstract reasoning.
In order to ascertain whether the sky is a hollow rotating
sphere surrounding the Earth, or whether it is, as now claimed,
a boundless ocean swarming with suns and worlds, let us
examine it and the various objects which appear to be " fixed "
to it, or to be wandering around on it.
The most noticeable of the permanent objects in the sky are
known as the Sun and Moon.
The most numerous and steadfast are called the "fixed " stars.
They were so named because they do not appear to change
places relatively to one another.
A few objects which very much resemble the stars in appear-
ance are distinguishable from them by several peculiarities.
For example, they do not twinkle like the stars, but shine with
a steady unflinching light. At some periods they shine very
much more brilliantly than at other times. And they slowly
change their places among the "fixed" stars. For this latter
reason they are known as planets, or " wanderers." The best
4 HOW TO KNOW THE STARRY HEAVENS
known of them go by the names of Latin deities who were
formerly identified with them. They are called Saturn, Jupiter,
Mars, Venus, and Mercury.
Oft-repeated observations of the heavenly bodies, from differ-
ent parts of our globe, long since proved that they all appear to
have certain definite and well-defined motions which have been
repeated over and over again for hundreds and thousands of
years. There are, to be sure, certain irregularities in some of
these motions, but close and long-continued observations show
that even these irregularities are themselves regular and cyclic
in their action.
STELLAR MUSIC
The most obvious of these motions may be imitated by tak-
ing two twelve-ribbed umbrellas (real or imaginary), opening
them both, and tying their handles together, so that the arrange-
ment forms a kind of globe (see Figure 2).
On the Equator. If the observer lives on the Equator, in
that hot circle of the Earth which lies between the Tropics, he
can represent the apparent motion of the star-strewn " sphere "
by keeping the handles of his umbrellas horizontal in a north-
and-south direction, and slowly spinning the whole thing
around on its handles, so that the rims of the umbrellas rise
in the east and descend in the west.
The names of the various groups of stars can be chalked on
the inside of the umbrellas, and the observer must imagine
himself standing (in the centre of the apparatus) on a flat
table which prevents him from seeing anything below his own
level. The chalk-marks which are near the rims of the um-
brellas will then seem to rise in the east, pass overhead, and
sink in the west. Those farther north and south will pass
more slowly over the handles or " poles " of the apparatus,
which lie flat on the central table and do not change their posi-
tion at all.
So long as the observer stays on the Equator there will be
no change in the position of the starry sphere, which appears
APPARENT MOTIONS OF HEAVENLY BODIES 5
to turn completely over in about four minutes less than twenty-
four hours. 1
It is obvious that, if we turn our apparatus so as to keep up
with the stars, a fresh rib will pass the Zenith, or point over-
head, every two hours (nearly), and that at the same instant
AS USED ON
THE EQUATOR .
*F
FIG. 2. UMBRELLA-APPARATUS FOR ILLUSTRATING (APPARENT) STAR
MOVEMENTS
Face the west when using this diagram. By reversing the points of the compass as here
given, and facing the east, it will represent the Earth's real motion.
the opposite rib will pass the Nadir, or point below. Also that
one rib will rise above the eastern horizon at the same time,
while another will descend below the western horizon.
1 If it were not for these four minutes' difference we should see the same stars,
in the same part of the sky, at the same time of the night, the whole year
through,
6 HOW TO KNOW THE STARRY HEAVENS
At the North Pole. But if the observer travels to the north,
the apparatus will not follow the motions of the stars unless
he tips it up by raising the northern umbrella. By the time he
reaches the frozen regions near the North Pole, he will have
to tip up the apparatus so much that the handles will be per-
pendicular. The southern umbrella will then be below, out of
sight, and the chalk -marks on the northern umbrella will turn
around the point overhead. If the observer now holds his
watch overhead, with the face down, he will find that the
chalk-marks are going the opposite way to the hands of the
watch.
At the South Pole. If the observer returns to the Equator,
he will have to turn the northern umbrella down again, and
when he sails into the southern seas the southern umbrella will
have to be tipped up, to represent the motions of the stars. By
the time he reaches the frozen regions around the South Pole,
the southern umbrella will be uppermost. A fresh set of chalk-
marks will then turn around the point over his head, and they
will be found to turn the same way that the hands of the watch
revolve when looked at from below.
During these supposed journeys from the Equator to the Poles,
the axis of the apparatus will not really le typed up either way,
for the northern stick will point to the North Pole-Star all the
time, and the southern stick will be directed toward the same
part of the southern skies all the time. The apparent tipping
up and down is due to the fact that the surface of the Earth
is not flat, but round, and therefore dips toward the Poles.
The annexed diagram will show this clearly, the large circle
representing the Earth, and the five small objects representing
our umbrellas in different parts of the world (see Figure 3).
SOLAR MUSIC
On the Equator. Let us suppose that the observer is again
on the Equator with his apparatus, and that he wishes to follow
the motions of the Sun. It will be necessary to put a hoop
over the umbrellas where the twelve pairs of ribs come together.
APPARENT MOTIONS OF HEAVENLY BODIES 7
This hoop will represent the Celestial Equator. The ribs of the
umbrellas should be numbered from 1 to 12.
Spring " Passover." If it is about the 20th of March, the
Sun's position can be represented by hanging a small electric
light where the equatorial hoop crosses the first pair of ribs.
On turning the apparatus as before, the electric light will rise
in the east, pass overhead, and set in the west. While it is
FIG. 3. THE EARTH, SHOWING RELATIVE POSITIONS OF APPARATUS WHEM
USED AT EQUATOR, POLES, ETC.
above the level of the imaginary observer in the centre of the
apparatus, the chalk-marks representing the stars must be
supposed to be out of sight, on account of the greater brilliancy
of the electric light. When it sets in the west, the chalk-
marks above the horizon must be supposed to come into view
again.
Autumnal Equinox. Six months later about Septem-
ber 22 the arrangement will be the same, except that the
8 HOW TO KNOW THE STARRY HEAVENS
light will have to be shifted to where the equatorial hoop
crosses the opposite or seventh pair of ribs. That is to say, if
the light was where the first pair of ribs come together in
March, it will be where the opposite or seventh pair of ribs
come together in September.
FIG. 4. UMBRELLA-APPARATUS MODIFIED FOR ILLUSTRATING APPARENT
MOVEMENTS OF SUN AND PLANETS
Face the west when using this diagram. If used north of the Equator, raise (N) till it
points to the North Pole, and vice versa. The feathered arrows indicate the diurnal mo-
tion; the plain arrows indicate the annual motion.
Midsummer Solstice. About June 21 the light will be on
the fourth rib, but will be some distance north of the equatorial
belt.
Yuletide Solstice. About December 21 it will be on the
tenth rib, but some distance south of the equatorial belt.
APPARENT MOTIONS OF HEAVENLY BODIES 9
If a second hoop be passed over the umbrellas, so that it will
pass over these four places, it will represent the Ecliptic, or
annual path of the Sun among the stars (see Figure 4).
It will be seen that the light representing the Sun does not
go its daily round exactly the same as the chalk-marks repre-
senting the stars. It moves slowly backward on the second
SUN
JUNE.
FIG. 5. CIRCLES OF THE CELESTIAL SPHERE WITH WORLD IN THE CENTRE
Only the upper half of the diagram is supposed to be above the horizon of the observer.
Face the west when using the diagram. Those living north of the Equator should raise (*
until the axis (SN) points to the North Pole-Star, and vice versa.
hoop, so that the average interval between one " mid-day " and
the next is nearly four minutes longer than the " southing " of
one of the chalk-marks on two successive " nights." The re-
sult is that in the course of 366J revolutions of the umbrellas,
which represent the star-sphere, there are only 365J revolutions
10 HOW TO KNOW THE STARRY HEAVENS
of the light which represents the Sun. In other words, the
Sun, whose motions we are trying to represent, creeps slowly
back along the Ecliptic, so that in exactly one year it has lost
one revolution, having gone completely around the " star-sphere "
to the place where it was twelve months before.
As the Sun's path is not on a line with the Equator, but
crosses it obliquely, the Sun not only loses one complete
revolution in a year, but also drifts to the north and south
of the equatorial belt, which it " passes over " twice in each
year, at the spring and autumn " Passover " or Equinox (see
Figure 5).
"THE BURNING ROW"
In the apparatus just used, the hoop along which the light
slowly travels represents the Celestial Ecliptic, or path of the
Sun. This hoop lies over twelve sets of chalk-marks repre-
senting twelve different constellations of stars. Each set of
stars has a name by which it has been known for several thou-
sands of years. The twelve form what are collectively known
as the Signs of the Zodiac. They are also known as the Twelve
Houses (or Mansions) of the Sun. The Book of Job (xxxviii, 32)
mentions them under the name of the Mazzaroth.
It takes the Sun a solar month (a little longer than a lunar
month) to travel through each " house " or constellation. In
March the Sun enters the constellation known by the Latin
name for Fishes (Pisces) ; in June it gets to the group known
as the Twins (Gemini) ; in September it reaches the Virgin
( Virgo) ; in December it is with the Archer (Sagittarius);
and the following March it enters once more the constellation
of Pisces. 1
1 The Sun is commonly said to be at the "First Point of Aries" (the Ram)
at the Spring Equinox. This is true only at certain long distant intervals, as
will be explained in Chapter XII. The "point" has reference to the Earth's
orbit, and not to the stars. It was named after the constellation which happened
at the time to be beyond the Sun in March.
APPARENT MOTIONS OF HEAVENLY BODIES 11
LUNAR MUSIC
The positions and motions of the Moon are about the same
as those of the Sun, only the Moon hangs back more and loses
a revolution in a lunar " moonth," or month, instead of losing
one in a year. In its backward drift it therefore catches up
with the Sun nearly thirteen times in a solar year.
Eclipses. The various phases of the Moon show that it is
a dark body, like our Earth, lighted up on one side by the Sun.
They also show that it is nearer to us than the Sun. Some-
times, indeed, it passes exactly between us and the Sun, pro-
ducing what is known as an Eclipse of the Sun. When it is
opposite to the Sun, the shadow of the Earth sometimes falls
on it, producing what is known as an Eclipse of the Moon. The
reason why there is not an eclipse at every " conjunction " and
" opposition " of the Sun and Moon is that the path of the lat-
ter, although nearly on the same plane as that of the Sun, does
not exactly coincide with it. The two paths, therefore, appear
to cross or intersect, in the same way that the Ecliptic and the
Equator cross each other.
PLANETARY MUSIC
The larger planets all keep on or near the Sun's path, but
their apparent motions are more irregular, and each has a period
of its own, varying from a few months to many generations.
Those known as Mercury and Venus appear to drift back-
ward and forward on each side of the Sun. They never go
very far from it, and are therefore seen only shortly before sun-
rise or soon after sunset.
The other planets appear to drift eastward among the stars
that lie along the path of the Sun and Moon. But when they
get nearly opposite to the Sun (that is, when they pass the
south about midnight) this eastward drift is reversed for a time,
so that each planet appears to make a loop in the star-sphere.
But they never go far away from the Ecliptic, or path of the
Sun (see Figure 97).
12 HOW TO KNOW THE STARRY HEAVENS
North and South of the Equator. If our observer takes his
apparatus north or south of the Equator, and tips it up as
before, when observing the stars, he will find that the positions
and motions of Sun, Moon, and planets can all be approximately
marked out on the hoop that represents the Ecliptic. This
will be true for any and every part of the Earth's surface. The
Moon and the large planets are never found in any other part
of the sky than on (or close to) the Sun's path, or Ecliptic. The
same apparatus will show why the days are long in June north
of the Equator, and long in December to the south of that line.
Going East and West. So far the observer has travelled
only north and south. If he travels to the east or west, he will
find that no change is needed in his apparatus so long as he
does not change his latitude.
On the Equator, for example, the motions of the heavenly
bodies are the same whether the observer is in Africa, the East
Indies, or in America. The only difference is in time. If he
could telegraph from equatorial Africa at midnight, and get
immediate answers from the East Indies and America, he would
find that it was already sunrise in the East Indies, whilst it
was only sunset in equatorial America. With this exception
the phenomena observed are alike on all parts of the Earth
lying under the Equator. The same is true of any other
latitude.
Although our apparatus represents very fairly the angular
distances and apparent motions of the heavenly bodies, it does
not directly throw any light on their actual distances or real
motions.
A PRIMITIVE EQUATORIAL
It will be well for all who have not made a study of the
above phenomena to observe for themselves as many of these
apparent motions as can be seen from the part of the world
they may happen to live in. All the apparatus that is really
necessary is a straight stick set firmly in the ground (or other-
wise supported) at such an angle that it will point to the Pole
APPARENT MOTIONS OF HEAVENLY BODIES 13
Star, and a tube (or telescope) attached to it so that it can be
moved in any direction. The tube or telescope can then be
rotated so as to follow the diurnal motion of any of the heav-
enly bodies. When the tube is at right angles to its support
it is pointing to the celestial Equator (see Figure 6). Rude
Fio. 6. AN ADJUSTABLE EQUATORIAL, SUITABLE FOR
ANY PART OF THE WORLD
The axis is clamped in such a position that its ends point to the
poles of the heavens.
as this method of observation may seem, it is capable of lead-
ing intelligent observers to a correct solution of the main prob-
lems of astronomy.
A very interesting method of observing the daily motions of
the stars is to point a camera to some part of the sky on a clear
starlight night, and leave the plate exposed for an hour or so.
On developing the print it will be found that each star has left
a trail on the plate. Figure 7 is a photograph of the stars sur-
14 HOW TO KNOW THE STARRY HEAVENS
rounding the North Pole. The further the star is from the
centre of rotation, the longer and straighter is the trail it makes
on the plate.
Figure 8 shows the constellation of the Great Bear (or the
Dipper, as it is often called), repeated four times, to show its
position in the northern skies every six hours. It will be seen
that the two " Pointers " are always in a straight line with the
star which happens to be near the axis of rotation. This star
is commonly known as (Stella) Polaris, or the Pole Star.
FIG. 7. NORTHERN STAR-TRAILS
Photographed by Barnard, with twelve hours' exposure.
FIG. 8. THE DIPPKR, OR GREAT BEAR, AT INTERVALS OF Six HOURS
It will be seen that the two "pointers" are always in a line with the Pole-star.
\
CHAPTER II
KIVAL THEORIES TO EXPLAIN THE APPARENT MOTIONS
OF THE HEAVENLY BODIES
(A) THE EARTH-CENTRED THEORIES OF THE UNIVERSE
"Then the Evening (Erev) and the Morning ( Voker) brought to a close the
Third Day ( Yom}.
"And the Mighty Ones (Elohim) said : ' Let there be luminaries in the Ham-
mered Plate (Rakia) of the sky, to separate the Day (Yom) from the Night
(Lylah}; 1 let them be for signs and to mark the seasons, Days (Yamim), and
years ; let them serve as luminaries, in the Hammered Plate of the sky, to give
light upon the Earth.' And it was so.
" And the Mighty Ones made two great luminaries, the larger one to preside
over the Day ( Yom), and the smaller one over the Night (Lylah). [They made]
the stars also.
" The Mighty Ones placed them in the Hammered Plate of the sky, to give light
upon the Earth, to preside over the Day (Yarn), and the Night (Lylah}, and to
separate the light from the darkness. The Mighty Ones saw that it was good.
"Then the Evening (Erev} and the Morning (Voker} brought to a close the
Fourth Day (Yom}." Book of Origins, I, 13-19 (A. ZazeVs Translation).
EARLY FLAT-WORLD SUPPOSITIONS
IN trying to explain the observed motions real (or apparent)
of the heavenly bodies the ancients were handicapped by
their ignorance of the world itself. This appeared, from their
local standpoint, to be a flat though uneven surface, the lower
parts of which were filled with water. Their experiences on
this Earth also prevented them from realising the possibility of
anything solid and heavy remaining suspended in space without
falling anywhere. Their entire ignorance as to the nature,
dimensions, and distances of the celestial bodies led them to
1 Lylah was personified by the Israelites as Lilith, the first wife of Adam.
Isaiah xxxiv, 14 (R. V. Margin).
16 HOW TO KNOW THE STARRY HEAVENS
suppose that they were put in the heavens by somebody to throw
light on the Earth, or to relieve the monotony of the sky. With
them the Earth itself was the Universe, and even those who
recognised the importance of some of the most prominent celes-
tial objects made the natural mistake of supposing them to be
Gods who ruled the Earth from their thrones on high.
UNDERLYING FACTS
Yet even three and four thousand years agone there were
individuals who had discovered that " things are not what they
seem." Some of the real facts relating to the Universe were
known to a few learned men among the ancient Babylonians,
Egyptians, Chinese, Greeks, and Hindus. But the world was
not ready for their teachings, and during the Dark Ages that
followed the establishment of Christianity the few truths that
were known were trampled under foot, like pearls cast before
swine.
However, trampled pearls are apt to come to light again.
Facts are stubborn things, and will not permanently down.
So the lost facts have been rediscovered in modern times, and
largely supplemented by fresh ones.
Let us glance briefly at some of the primitive ideas held by
the ancients with regard to the Universe, so that we may com-
pare them with more modern explanations. We can then decide
as to which best fit the observed phenomena, and are, on that
account, the most deserving of credence.
THE CANOPY THEORY
The world we live in was at first supposed to be flat, or nearly
so, with a massive firmament resting on the mountains at the
edge and spanning the whole Earth.
To the ancient Egyptians the sky was the bosom of Neit, a
celestial ocean across which the divine Sun, Moon, and planets
were carried in boats. In Greece it was supposed to be a solid
canopy, across one part of which Helios, the Sun-God, daily
RIVAL THEORIES 17
drove in a chariot of gold, while his sister Selene, the Moon-
Goddess, followed him in a chariot of silver. Mount Olympus
was supposed to reach up to the highest part of this canopy.
On the summit of this holy mountain was the palace of Zeus,
king of all the Gods. There the Greater Deities abode, ruling
the world below to suit themselves, and dealing out a very pecu-
liar kind of justice to the unfortunate mortals who lived thereon.
Ancient books, as a rule, did not discuss or assert these things,
any more than modern books discuss or assert the conclusions
of modern astronomy. They merely alluded to them, taking them
for granted as well-ascertained facts which were useful for illus-
tration, but which it would be folly to argue about or assert.
Thus one of the characters in the Hebrew drama of Job casu-
ally mentioned that this firmament was " spread out " (Job ix, 8)
"as strong as a molten mirror" (Job xxxvii, 18 R. V.). In
the same way the Mohammedan Koran sought to show the fine
workmanship of Allah by pointing out that he had stretched the
firmament across the entire world without a crack in it.
The Hebrew word for firmament (Ralda) really means a ham-
mered plate of metal (Ex. xxxix, 3), and all its Greek and Latin
equivalents have afirm or solid meaning. The modern idea that
the writers meant an expanse is seen to be absurd when we notice
that it was created (Gen. i, 1), or made (Gen. i, 7) ; that it was
spread out over the Earth (Job ix, 8) ; and that it had windows
in it (Gen. vii, 11) ; also that the Tower of Babel was intended
to reach up to it (Gen. xi, 4) ; and that the top of Jacob's ladder
rested against it (Gen. xxviii, 12). The mountains which were
supposed to support this " hammered plate of heaven " were natu-
rally spoken of as the pillars of heaven (Job xxvi, 11).
When the writer of the Apocalypse was describing the ap-
proaching end of the world he made an earthquake shake the
stars out of this firmament on to the ground " as a fig-tree casteth
her unripe figs when she is shaken of a great wind." He ended
by letting the heavens roll together, as a scroll does when the
ends are released (Rev. vi, 13-14 R. V.).
The Venerable Bede, an eminent Christian writer of the
2
18 HOW TO KNOW THE STARRY HEAVENS
seventh century, considered the Earth to be flat (or perhaps
convex), with a star-spangled canopy over it. This canopy he
supposed to be like an umbrella, with its centre at the Pole
Star. The daily motion of the heavenly bodies he explained
by supposing the canopy to spin round, like the tent over the
" merry-go-rounds " of our country fairs. His ideas on the sub-
ject are a curious mixture of accurate observation and childlike
speculation. He says :
" The Creation was accomplished in six days. The Earth is its
centre and its primary object. The Heaven is of a fiery and subtile
nature, round and equidistant from every part, as a canopy from the
centre of the Earth. It turns round every. day with ineffable rapidity,
only moderated by the resistance of the seven planets, three above
the Sun Saturn, Jupiter, Mars then the Sun ; three below
Venus, Mercury, the Moon. The stars go round in their fixed courses,
the northern perform the shortest circle. The Highest Heaven . . .
contains the angelic virtues. . . . The Inferior Heaven is called the
Firmament, because it separates the superincumbent waters from the
waters below."
THE CRYSTAL SPHERES
Such were the primitive ideas of unenlightened men with regard
to the Universe. Sometimes, however, the problem was investi-
gated in a scientific spirit. It was then readily seen that the
celestial phenomena could not be explained on the canopy
theory.
Observation, as well as theory, ultimately led to the overthrow
of this primitive idea of a solid star-strewn firmament resting
on the mountains. For many of these so-called "pillars of
heaven " had been ascended, and no " hammered plate of
heaven" had been found resting on them.
So new theories arose, each of which came a little nearer the
truth than the one before. It was suggested that the world was
inside a crystal globe or sphere, to which the stars were attached.
The nightly motions of the stars were explained by supposing
that this crystal sphere rolled over every twenty-four hours.
RIVAL THEORIES
19
This theory explained very well the motions of the stars, but
did not fit in with the more varied movements of the Sun, Moon
and five planets. Some explained their irregularities of motion
by supposing that they were carried around with the stare, but
that, instead of being fixed to the revolving sphere, like the stars,
they were at liberty to crawl around on it very slowly, like so
FIG. 9. THE PTOLEMAIC SYSTEM
many insects. Others suggested that each of these seven wan-
derers had a crystal sphere all to himself (see II Cor. xii, 2).
The seven spheres were supposed to be one inside the other.
Each was thought to share in the general daily rotation, but to
lag behind or have a slight independent motion of its own (see
Figure 9).
Even this far-fetched notion did not fit in satisfactorily with
the observed phenomena. So Tycho Brahe* suggested that the
Earth was a globe, spinning round on its axis every twenty-four
20 HOW TO KNOW THE STARRY HEAVENS
hours ; that the Sun and Moon went around the Earth in a year
and in a month, respectively ; and that the five planets went
around the circling Sun (see Figure 10).
FIG. 10. THE TYCHONIC SYSTEM
EPICYCLES
As even this complex arrangement did not fit in with the
observed motions, the planets were then supposed to move in
a series of eccentrics around their ideal orbits, with the star-
sphere outside of all. For a time this theory was thought to
explain the observed motions. But it was such a complex,
improbable, lumbering, incomprehensible, and absurd theory
that Alphonso, king of Castile, ventured the remark that if he
had been consulted by the Creator he could have considerably
improved upon the plan.
RIVAL THEORIES 21
FAUSTUS ON THE SPHERES
These mediaeval speculations are well illustrated by the fol-
lowing dialogue from Marlowe's " Faustus" written toward the
close of the sixteenth century.
" Faust. Tell me, are there many heavens above the Moon ?
Are all celestial bodies but one globe,
As is the substance of this centric Earth ?
Mephistopheles. As are the elements, such are the spheres,
Mutually folded in each other's orb.
And, Faustus,
All jointly move upon one axletree,
Whose terminine is termed the World's wide pole :
Nor are the names of Saturn, Mars, or Jupiter
Feign'd, but are erring stars.
Faust. But, tell me, have they all one motion, both situ et tempore ?
MepJi. All jointly move from east to west in twenty-four hours upon
the poles of the World, but differ in their motion upon
the poles of the zodiac.
Faust. Tush, these slender trifles Wagner can decide :
Hath Mephistopheles no greater skill?
Who knows not the double motion of the planets?
The first is finished in a natural day;
The second thus; as Saturn in thirty years, Jupiter in twelve;
Mars in four ; the Sun, Venus, and Mercury in a year ;
the Moon in twenty-eight days. Tush, these are fresh-
men's suppositions. But, tell me, hath every sphere a
dominion or intellitjencia ?
Meph. Aye.
Faust. How many heavens or spheres are there ?
Meph. Nine ; the seven planets, the firmament, and the empyreal
heaven.
Faust. Well, resolve me in this question ; why have we not con-
junctions, oppositions, aspects, eclipses, all at one time,
but in some years we have more, in some less ?
Meph. Per incequalem motum respectu totius.
Faust. Well, I am answered."
22 HOW TO KNOW THE STARRY HEAVENS
The writer of a recent magazine article l sums up these old
ideas of the Universe very neatly. He says :
" To the men of the Middle Ages the world was a little space shut
tight within a wheelwork of revolving spheres. It was compendious,,
complete, ingenious, like a toy in a crystal box. Beyond the outer
shell nothing existed. The heavens were uncorruptible. No change
could occur in the whole system, save in the Earth alone. The Uni-
verse was created for the sole use of man. It was small and finite."
THE ROUND WORLD
While all these speculations were going on, people had been
going to and fro on the Earth, and travelling up and down on
it. In this way they had discovered for an actual fact that the
world is not flat, but is a round ball, 8,000 miles thick, suspended
in space, with the starry heavens on every side of it.
This being the case, it follows that if the stars are fixed to a
massive firmament, it is not a mere " dish-cover " or umbrella
over a flat Earth, but is in the form of a hollow crystal sphere,
rolling over (to the west) every twenty-four hours, with the round
World in the centre, supporting itself on nothing.
(B) THE SUN-CENTRED THEORY OF COPERNICUS.
"The first formal assertion of the heliocentric theory was made in
a timid manner, strikingly illustrative. of the expected opposition. It
was by Copernicus, a Prussian, speaking of the revolutions of the
heavenly bodies ; the year was about 1536. In his preface ... he
complains of the imperfections of the existing system, states that he
has sought among ancient writers for a better way, and so had learned
the heliocentric theory. ... In their decree prohibiting [the work of
Copernicus], ' De RevolutionilmsJ the Congregation of the Index,
March 5, 1616, denounced the new system of the Universe as 'that
false Pythagorean doctrine utterly contrary to the Holy Scriptures.'
. . . The opinions thus defended by the Inquisition are now objects
of derision to the whole civilized world." 2
1 Dr. E. S. Holden, in the " Popular Science Monthly," November, 1903.
2 Dr. J. W. Draper.
RIVAL THEORIES 23
" People gave heed to an upstart astrologer who strove to show that
the Earth revolves, not the heavens or the firmament, the Sun and
Moon. . . . This fool wishes to reverse the entire science of astronomy." l
The final outcome of all these speculations was that the whole
of the Earth-centred theories were thrown overboard, and re-
placed by an old Sun-centred theory originally brought from
India by Pythagoras. According to this new yet ancient theory,
the stars are practically immovable bodies suspended far off in
space, and the Sun is the centre around which all the planets,
including the Earth itself, revolve (see Figure 11).
FIG. 11. COPERNICAN SYSTEM
Including four of the most tilted orbits of Minor Planets. Neptune's orbit is here omitted.
It has been found, however, that the Moon does actually go
around the Earth, completing a revolution in about a month.
The daily motion of all the heavenly bodies is not real, but only
apparent. It is explained by the fact that the Earth itself rolls
completely over (to the east) every twenty-four hours, at the
same time that it travels around the Sun once every year. This
daily rotation of the Earth causes all the heavenly bodies to
appear to turn in the opposite direction.
The peculiarities of the Sun's annual drift to the north and
south, and the resulting seasons, are readily explained by the
l Martin Luther.
24 HOW TO KNOW THE STARRY HEAVENS
fact that the Earth has a. heavy " list " to one side, with reference
to its path around the Sun (see Figure 12). The other planets
are also drifting around the Sun, in the same general direction,
but at different distances from it.
This Indian system of cosmogony is now known as the Coper-
nican Theory, because Copernicus first established its truth in
modern Europe. It explains the motions of the heavenly bodies
so well that there is no doubt about its being true as far as it
FIG. 12. RELATIVE POSITIONS OF EARTH AND SUN AT THE FOUR SEASONS
goes. In spite of the long-continued opposition of unprogres-
sive theologians, it has now been adopted by all competent
judges, and is accepted, on hearsay, even by those who do not
realise the subordinate position to which it reduces our Earth,
and by those who do not profess to be competent to judge as to
its correctness.
The adoption of this theory has led to the solution of a mul-
titude of otherwise inexplicable phenomena. Without it, the
planetary bodies appeared to be swinging around us in a labyrinth
of perplexing knots and meaningless tangles. As a result of its
adoption, the knots and tangles have all been unravelled, and
the structure and dimensions of the Solar System have been
RIVAL THEORIES 25
tolerably well ascertained. The telescope and other opitical in-
struments have now greatly increased our knowledge of the
heavenly bodies generally, and have revealed to us similar sys-
tems moving in actual conformity with the Copernican Theory.
This same theory has also enabled astronomers to apply them-
selves, not entirely without success, to the task of ascertaining
the structure, and measuring the distances and dimensions, of
the more distant luminaries known to us by the misleading name
of " fixed stars."
Every observed peculiarity is explained by this theory, without
any absurd and impossible suppositions like the " eccentrics "
and " epicycles " of other theories. And many facts have been
discovered by following it up to its logical conclusions. It is
therefore the true explanation of the mechanism of the Universe.
How and why these movements of the heavenly bodies are
kept up will be briefly dealt with in subsequent chapters.
CHAPTER III
PRINCIPLES UTILISED FOR MEASURING THE UNIVERSE
"And there was given me a reed like unto a rod, and the angel stood, saying,
Rise and measure the temple of God." Rev. xi, 1.
"And he that talked with me had a golden reed to measure the city, . . .
and he measured the city with the reed, twelve thousand furlongs. The length
and the breadth and the height of it are equal." Rev. xxi, 15, 16.
"The measure of the Moon's distance involves no principle more abstruse than
the measure of the distance of a tree on the opposite side of a river." Sir George
Airy.
HOW IT IS DONE
I WILL now say a few words about the way in which as-
tronomers have been enabled to find out the distances and
dimensions of many of the objects which -compose the L T ni verse.
It was very early recognised that the heavenly bodies are not
all at the same distance from us.
STARS ARE BEYOND PLANETS
The stars, for example, have a far-away look and a fixity of
position that would naturally lead one to think that they were
beyond the larger, brighter, and more active luminaries which
are found on or near the Ecliptic. This was proved beyond a
doubt when observers at a distance from one another compared
notes. For it was sometimes found that when an observer in
the north saw a certain planet a little to the south of a particu-
lar star, an observer in the south would see it north of the same
star. The only possible explanation of this is that the planet is
nearer to us than the stars.
THE ORDER OF THE PLANETS
Leaving the " fixed " stars out, there were seven celestial
" wanderers " known to the ancients. Of these, two appear to
PRINCIPLES FOR MEASURING THE UNIVERSE 27
be very much nearer to us than the other five. The Sun, for
example, is evidently either very near or very large, bright, and
hot. But the Moon is nearer to us than the Sun, for it some-
times passes in front and shuts off its light and heat from us.
As it also passes between us and every other celestial object
that comes in its way, it is evidently the nearest of all the
heavenly bodies.
Now the Moon performs its circuit of the heavens in less time
than any other wanderer. It seems natural, then, to suppose
that the wanderers which take the most time to perform their
circuit are the farthest away from their common centre of
revolution.
This reasoning led the early astronomers to regard slow-moving
Saturn as the most distant planet. The stately Jupiter they
put next, followed by fiery Mars. As regards the other three,
there was some difference of opinion, due to the fact that, on the
Earth-centre theory, their real motions were not distinguished
from their apparent ones, due to perspective.
But when once it was recognized that the Sun was the centre
around which the planets turned, it became evident that our own
populous Earth and pale-faced Moon were travelling in partner-
ship, next to Mars ; that " Venus the beautiful " followed ; and
that fast-flying Mercury kept nearest to the central Sun.
COMPARATIVE DISTANCES
The order of the planets being thus settled, the next thing
was to ascertain their distances from the Sun.
In the case of the inferior or inner planets, Mercury and
Venus, their proportional distances from the Sun were easily
found. All that had to be done was to point one leg of a pair
of dividers, or compasses, at the setting or rising Sun, and the
other leg at the planet Venus when at its greatest angular dis-
tance from it, as an Evening or Morning Star. The dividers
were then laid on a sheet of paper, and two lines drawn
to indicate the V shape of the open dividers (see S E V in
Figure 13).
28 HOW TO KNOW THE STARRY HEAVENS
The Earth was then supposed to be at E, where the two lines
come together, and the Sun was supposed to be at the other end
(S) of one of the lines. Venus would evidently be somewhere
on the line E V.
Taking it for granted that the planetary orbits were circular,
a circle was then drawn through E from S as a centre. This
represented the Earth's or-
bit. Another and smaller
circle was drawn from the
same centre, just large
enough to touch the other
arm, E V. This circle
evidently represented the
orbit of the planet Venus.
The same process was
gone through with the
planet Mercury, and the
result transferred to the
same figure (see S E M).
On measuring the radii
or semi-diameters of these
three circles, representing
the planetary orbits, it was found that their lengths varied
in the ratio of 100, 72, and 38. These figures, therefore,
represent the relative distances of the Earth, Venus, and
Mercury.
A comparison of the distances with the times of revolution
then enabled the relative distances of the superior or outer
planets to be computed by means of their times of revolution,
taking it for granted that they all obeyed the same law, what-
ever that law might be.
The result was that the distances of the outer planets, when
computed on the same scale as the inner ones (=100 to the
Earth's distance), were found to be 152, 520, and 953.
FIG. 13. ORBITS OF MERCURY, VENUS,
AND EARTH
PRINCIPLES FOR MEASURING THE UNIVERSE 29
PLANETS MOVE IN ELLIPSES
It may be as well to state here, that while the above observa-
tions were being made it was discovered that the orbits of the
inner planets are not exactly circular, but slightly egg-shaped,
or, rather, elliptical. It has since been found that the paths of
all the planets share this peculiarity, the cause of which has
also been ascertained.
NEWLY DISCOVERED PLANETS
Since the invention of the telescope two large planets have
been discovered beyond the orbit of Saturn. They bear the
names of Uranus and Neptune. On the same scale as that used
above, their distances from the Sun are represented by the
numbers 1,920 and 3,000.
A great number of small planets have also been discovered in
the interval between the orbits of Mars and Jupiter. Their
numbers are so great, their sizes so small, and their orbits so
peculiar, that astronomers formerly looked upon them as the
scattered fragments of larger planets which had met with an
accident. 1
ACTUAL DISTANCES
The comparative distances of all the planets having been thus
discovered, all that had to be done was to find the real distance
of one of them in miles. All the other distances could then be
readily computed in miles.
It took many generations to solve this little problem, and even
yet the answer is not as free from error as could be wished. It
has, however, been solved, with a very fair amount of accuracy,
by several independent methods. The distances usually meas-
ured are those of the neighbouring planets when they are at
their least distances from us or are otherwise favourably placed.
1 The orbits of four of these " Asteroids " are shown in Figure 11. It will be
noticed that the four represented do not lie in the same general plane as those of
the larger planets, but are more or less tilted up, some one way, and some another.
These, however, are exceptions. The majority move in or near the general plane.
30 HOW TO KNOW THE STARRY HEAVENS
There are many people who do not put much faith in celestial
measures. They cannot see any possibility of obtaining them,
seeing that we cannot stretch a tape-line from one flying world
to another. There are, however, a number of ways in which in-
accessible distances may be accurately measured. For example,
if you wish to measure the height of a tree without ascending
it, all you have to do, if the ground is level, is to put a stick
upright in the sunshine, and measure the length of its shadow.
If a three-foot upright makes a three-foot shadow, then a hun-
dred-foot shadow indicates that the tree which casts it is a
hundred feet high. And if the Sun is so low down that the
three-foot stick makes a six-foot shadow, then a two-hundred-
foot shadow will indicate that the tree which casts it is a hundred
feet high.
There are other methods which are just as simple, though
most of them require more elaborate apparatus. A little study
will show that celestial and other inaccessible measurements
may be as accurate as any made with the help of a chain or
tape-line. Let us see what are the principles involved and
methods employed.
ESTIMATING DISTANCES
If you close one eye and keep your head still, you will find
that with one eye alone you will be unable to judge as to the
distance from you of the object you are looking at. The only
exception to this is, that if you already know the size of the
object you can estimate its distance by noticing whether it
appears to be large or small.
To be able to estimate your distance from any object, you
must either move your head or open the other eye, so as to
get another picture of it to compare with the image already ob-
tained. Then you can estimate with a tolerable amount of
accuracy how far the object is from you (see Figure 14).
The two eyes form the extremity of a three-inch base-line,
and if you draw an imaginary line from each eye to the point
you are looking at, you will obtain a three-cornered or triangular
PRINCIPLES FOR MEASURING THE UNIVERSE 31
figure of known dimensions. That is, you will know (approxi-
mately) the length of all its three sides.
LAND-SURVEYING
The surveyor, when he wishes to find the width of a river
without crossing to the other side, measures off a base-line on
his own side of the stream. Then, by noting with his instru-
ments the position of an object on the other side of the river, as
his base-line, he
river is.
either calculate the
result by means of
FIG. 14. ESTIMATING DIS-
TANCES WITH THE EYES
seen from each end of
can tell how wide the
In this case he can
distance, or get the
a diagram on paper.
If he wishes to do the
latter, he draws a line
to represent his base-
line, and from each
end of it sets off a line
at the same inclination
or angle to it as that used on his real base-line. The place
where these two lines cross each other represents the position
of the object observed on the other side of the river (see Figure
15). By measuring the sides of his triangle he gets the dis-
tance required in terms of his base. For instance, if the sides
of his triangle are 10 times as long as the base thereof, and
the latter is 10 yards long, then the width of the river is 100
yards. 1
A whole continent can be surveyed in the same way, by
measuring off three-cornered areas of land, and using every dis-
tance obtained as a base to measure other distances with. In
this way (with certain details and precautions which need not
be here specified) the shape and size of the Earth can be
obtained.
1 A right-angled triangle gives the best results. Those who wish for further
details will find them in the next chapter, which is written for those who are not
afraid of a little simplified trigonometry and diluted mathematics.
HOW TO KNOW THE STARRY HEAVENS
SKY-SURVEYING
The astronomer then finds out the distance of the Moon in
the same way, by using a measured base-line about 4,000 miles
long. As he cannot see one end of his base-line from the other
end of it, he gets his angles indirectly, by polar distances, or by
observing how much the Moon is displaced among the stars
when viewed from different parts of the world at the same time.
The same principle, rather differently
applied, enables him to tell the distance
of the Sun.
With a 4,000-mile base-line the
Moon's distance is found to be about
60 times as long as the base-line. On
multiplying 4,000 by 60 we get the
Moon's distance, 240,000 miles. 1
With the same base-line of 4,000
miles the Sun's distance is found to be
about 388 times greater than that of the
Moon. It will be seen that the longest
base-line we can get is very short when
compared with the distance to be meas-
ured ; but as it is the longest available,
astronomers have to make up for its
shortness by using different methods and taking advantage of
every favourable opportunity to correct their measurements.
Now 388 times 240,000 comes to about 93,000,000 miles, which
is approximately the Earth's distance from the Sun.
As we already know the comparative distances of the other
planets from the Sun, their actual distances can now be obtained
without difficulty.
The following table gives in one column the relative distances
of the planets, the Earth's distance being represented by 1.000.
In another column it gives the real distances in miles. They
are calculated according to the most recent estimates of the
solar parallax, which will be explained in the next chapter.
1 These figures are not exact, but will serve to show the principles involved.
FIG. 15. SURVEYING
FROM A BASE-LINE
PRINCIPLES FOR MEASURING THE UNIVERSE 33
PLANETARY DISTANCES
(Solar Parallax, 8.81")
RELATIVE
ACTUAL (IN MILES)
Mercury .
. . . .387
. . 35,909,000
. . . .723 .
. . 67,087,000
Earth
. . . 1.000
. . . 1.523
. . 141,384,000
Asteroids
( 2.080 .
'1 4.262 .
. . 193,000,000
. . 395,470,000
Jupiter .
.... 5.203 .
. . 482,786,000
Saturn
.... 9.538
. . 885,105,000
Uranus
.... 19.183 .
. . 1,779,990,000
Neptune
.... 30.055 .
. . 2,788,800,000
It will be seen by those who have followed the argument thus
far that there is no guessing about the process. It is a mere
matter of observation and calculation. In the first instance
given, the width of the river can be found by stretching a cord
across it, or the result can be tested in various other ways. In
the case of the Sun, Moon, and planets, the results can also be
tested in other ways, as well as by repeating the experiment
under different conditions. As soon as the observations can be
carried out without error, the distances can be obtained exactly.
But not before. 1
STAR DISTANCES
The stars are too far off for their distances to be measured by
a 4,000-mile base-line. But as it is found that the Earth in Jan-
uary is at an enormous distance from the place which it occupies
in July, the positions of the stars are observed at both periods,,
and compared together.
1 A few years ago it was discovered that one of the asteroids, or minor planets,
which goes by the name of Eros, moves in an elongated orbit, one part of which is
nearer to us than that of Mars. At certain periods this planet (which is only
about twenty miles thick) comes within a distance of 14,000,000 miles from the
Earth. By its means celestial distances will before long be much more accurately
known than they are now,
8
34 HOW TO KNOW THE STARRY HEAVENS
This gives a base-line of nearly 186,000,000 miles. But even
with this gigantic base there are only a few of the nearest stars
whose distances can be even approximately estimated. The
distance of the nearest of them is about 135,000 times as great
as the length of our enormous base-line. It is 9,000 times as
far off as Neptune, the outside planet in our system. About
sixty stars have measurable parallaxes, a few more have per-
ceptible ones, but all the others are at present out of reach in
the unsoundable depths of infinite space.
If our eyes were as powerful and accurate as the instruments
of the astronomer, we could look at a shining grain of sand
thirty miles away, and estimate its distance from us by observ-
ing how much the eyes had to be drawn together to focus on
the object.
The same principle of triangulation which enables a surveyor
to plot off a township or measure the height of a mountain en-
ables the astronomer to measure the world and ascertain the
distances of the Sun, Moon, planets, and some of the stars.
Enormous as many of the distances are, all these measure-
ments depend on an ordinary yard-stick, they are all based
on the common three-foot rule.
"E PUR SI MUOVE"
It should be observed that the above-described method of
measuring the distances of the heavenly bodies will in some
cases give the same results whether we suppose the Earth to
stand still, with the Sun, Moon, planets, and stars swinging
around it once every twenty-four hours, or whether we suppose
that the diurnal changes are caused by the Earth revolving on
its axis.
But, having once found the distances, it is evident that the
latter is the true explanation of the phenomena. For if the
planet Neptune distant as it is really goes around the Earth
in a day, it must go at the unthinkable speed of 190,000 miles
in a second of time. And if the stars, whose distances are so
much greater than that of Neptune, also go around the Earth
PRINCIPLES FOR MEASURING THE UNIVERSE 35
every day, their speed must be thousands and millions of times
faster still.
On the other hand, if it is the Earth that revolves, the motion
is nowhere greater than one mile in three seconds. The proba-
bilities are evidently altogether in favour of the latter proposi-
tion. The former one is impossible and absurd.
There is only one way of getting over the difficulty. In spite
of all who deny it, or fail to realise it, the fact still remains that
" the Earth does move."
MEASURING THE PLANETS
While measuring the distances of the Sun and planets, astron-
omers have been able, by measuring their apparent diameters
(in degrees, minutes, and seconds of arc), to ascertain their real
diameters in miles. The principle is a very simple one, and
may be illustrated in this way.
A two-inch ball is 8 times as large as a one-inch ball (2 x
2x2 = 8). But if a one-inch ball is viewed from a distance of
ten feet, it will be just large enough to hide a two-inch ball
twice as far away, or a four-inch ball four times as far away.
Now, suppose that we have found the Moon to be 239,000
miles away. Let us get a ball 11 feet 5 inches in diameter, and
place it in a conspicuous position on the top of a steep mountain.
Having done so, let us measure off 1,262 feet (which is the one-
millionth part of the Moon's distance), to a place where the ball
will come between us and the rising or setting Moon. It will
be found that the ball is just large enough, at that distance, to
hide the Moon from us. Now, as the Moon is just a million
times as far from us as the ball which hides it, it follows that
its diameter is just a million times greater (11 feet 5 inches
X 1,000,000 = 2,162 miles).
So far, so good. It is interesting to note that, in an eclipse
of the Sun, the Moon acts the part of the ball just used.
It so happens that, while the Sun's average distance from us
(92,790,000 miles) is about 388 times that of the Moon (239,000
miles), his diameter (864,000 miles) exceeds hers (2,162 miles)
36 HOW TO KNOW THE STARRY HEAVENS
in about the same proportion. They therefore look as though
they were about the same size, although the Sun's diameter is
really almost 400 times as long, and his bulk is more than
60,000,000 times as great (400 x 400 x 400 = 64,000,000).
Most of the planets have no measurable diameter when seen
by the naked eye, but by means of the telescope their dimen-
sions also have been ascertained. The stars cannot be measured
in this way, as they are so far off that they have no perceptible
size, even when seen through the most powerful telescopes.
The amount of light we receive from them is almost the only
guide we have to their size, and even this is of no avail unless
we know something of their distances from us.
WEIGHING THE PLANETS
One of the most astonishing things that astronomers have
been able to do is to weigh the Sun and planets, so as to ascer-
tain their mass or weight. 1 Yet the principle is as simple as
that used in ascertaining their dimensions.
Get a light straight stick, and make a 'sharp point at each end
of it. Then stick a potato on each point, and hang the appa-
ratus from the ceiling by a string. Shift the string on the stick
till the potatoes balance one another. Now give it a twirl and
release it. The two potatoes will swing around the common
centre of gravity, where the string is fastened to the stick.
If the two potatoes are of the same weight, the centre of
gravity will be the same distance from each of them, and it
will be found that each one swings around the other one in the
same sized circle. But if one is heavier than the other, the
centre of gravity will be nearer to the heavy one, and it will be
found that the small one makes the largest circle. The appa-
ratus, indeed, makes a primitive pair of scales with which the
relative weight of each potato can be ascertained by noting the
size of the circle it makes.
1 These terms are not absolutely identical. The word mass refers to the amount
of matter contained in anything, while weight has reference also to the force of gravi-
tation, which varies iu different worlds. The distinction is not important here.
PRINCIPLES FOR MEASURING THE UNIVERSE 37
Now the Earth aud Moon form a similar weighing-machine.
They are all the time swinging around their common centre of
gravity, like our two potatoes, and their relative weights can be
found by the same process.
But at the same time that the Earth and Moon are swinging
around their common centre of gravity, the Earth-Moon family
on the one hand, and the Sun on the other, are also swinging
FIG. 16. DAILY POSITIONS OF EARTH AND MOON
It will be seen that the lunar path is always concave towards the Sun.
around their common centre of gravity. In this case the Earth
and Moon together are so small, in comparison with the Sun,
that they are doing nearly all the swinging. Nevertheless the
Sun is doing his part of the motion, even if it is too small to be
easily perceived.
All the members of our Solar System (including even the
Sun) swing around their various centres of gravity and influence
one another in the same way, the amount of their influence
depending on their mass and distance. The Sun outweighs all
the planets 745 times, so that his part of the swinging is very
small. Still it exists, and although it is convenient to say that
the Moon swings around the Earth, and that the Earth swings
around the Sun, it would be more correct to say that the Earth
and Moon swing around their common centre of gravity, and
that the Earth-Moon family and Sun do the same.
It will be seen that any family of worlds can be used as a
weighing-machine, with which the relative weight of each indi-
vidual can be ascertained by its influence over the other mem-
bers of the family. Some of the stars, even, can be weighed
against one another when they belong to one family.
38 HOW TO KNOW THE STARRY HEAVENS
ACTUAL WEIGHT
When we have found the relative masses or weights of the
Sun and planets, we can, by finding the actual weight of one of
them, in tons, find the actual weight of any, or all of them, in
tons.
The readiest way of doing this is to weigh the Earth and find
out how many tons of material it contains. Of course this is a
very easy thing to do. All that appears to be necessary is to
get a very strong weighing-machine, turn it upside down, so that
the Earth rests in the pan, and then adjust the scale and read
off the weight.
This last item must not be taken too seriously. The problem
of weighing the Earth is really one of the most difficult tasks
astronomers ever undertook. It has been solved, however, by
several different methods, 1 and it is interesting to know that the
Earth weighs about 6,600 millions of millions of millions of
American tons (6,600,000,000,000,000,000,000). And the Sun
contains 330,000 times that amount of material.
1 The best plan is one which employs a torsion -balance to measure the mutual
attraction of lead balls at known distances from one another. This is then com-
pared with the observed attraction of the Earth for the same lead balls, which are
known to be at a distance of about 4,000 miles from the centre of attraction. The
mutual attraction of the balls being known, the law of gravitation shows how dense
the World must be in order to give the balls their observed weight. (See Chapter
XV for the key to this problem. )
CHAPTER IV
SOME PROBLEMS USED IN CELESTIAL MEASUREMENTS
"The methods used for measuring astronomical distances are in some applica-
tions absolutely the same as the methods of ordinary theodolite surveying, and are
in other applications equivalent to them. . . . There is nothing in their principles
which will present the smallest difficulty to a person who has attempted the common
operation of plotting from angular measures." Sir George Airy.
IN order that the beginner may better understand the prin-
ciples upon which celestial measures depend, a few examples
are given here, going further into details than in the preceding
chapter. I do not undertake to say that everyone will be able
to follow them all ; but I have simplified them and explained
the terms as much as possible, so as to help a non-mathematician
who is willing to try.
DEGREES IN A CIRCLE
In trigonometry, which deals with the properties of three-sided
figures, we (after the Greeks) divide the circumference of a circle
into 360 degrees of arc, denoted thus (360).
These degrees are indicated by straight lines radiating from
the centre of the circle, which is supposed to be the point of
observation.
Where two of these radiating lines enclose a square corner or
right-angle, that angle evidently contains 90 of arc as measured
off on the circumference.
Each degree is, for convenience, divided into 60 minutes ('),
and each minute into 60 seconds (") of arc. These minutes and
seconds of arc have nothing whatever to do with minutes and
seconds of time. It is a mere accident (and misfortune) that
they are called by the same names.
40 HOW TO KNOW THE STARRY HEAVENS
Each line going from the centre to the circumference (like a
spoke in a wheel) is termed a radius (plural radii).
RADII AND ARC OF CIRCLE
It has been found that when two radii are so placed that the
central corner or angle contains 57 17' 45" (= 206,265"), then
the arc of circle cut off by the two radii is just equal in length
to one radius. 1 Such an arc is termed a radian.
FIG. 17. ARC OF CIRCLE
It naturally follows from this that when the angle is half of
that just given then the arc cut off is just half as long as each
radius (see Figure 17).
This is expressed as follows :
Let A B represent arc of circle
" Z " size of angle
" Y " radius of circle
" X angle of 57 17' 45"
Then when Z = X, A B = Y
When Z = JX, A B = j Y
WhenZ = JX, A B = JY
And so on.
1 That is, the part of the tire which is cut off would be, if straightened out,
just as long as one of the spokes,
PROBLEMS IN CELESTIAL MEASUREMENTS 41
The result is, that if we know the distance of an object in miles,
we can tell its diameter in miles by measuring the angle enclosed
by its opposite sides. For example, if an object 15 miles away
is long enough to subtend an angle of 3 49' 11" (=y a ^ of X),
then it must be about a mile long.
On the other hand, if we know the diameter of an object in
miles, we can tell its distance from us in miles. For example,
if we know that a certain object is a mile long, and we find by
FIG. 18. CHORD OF ARC
our instruments that it subtends an angle of 3 49' 11" (= & of X),
then it must be about 15 miles away.
These two things can be ascertained; however, only when the
distant object is near enough to have a measurable size when
seen through a telescope.
THE CHORD OF AN ARC
For many purposes it is convenient to draw a straight line
cpnnecting the outer ends of the two radii. This line is called
a chord, and the three straight lines together form what is known
as a triangle (see Figure 18).
In such a triangle the two outside corners or angles, A and B,
are equal to one another, and are each sharper or more acute
than a right angle. This is true whether the centre angle Z be
42 HOW TO KNOW THE STARRY HEAVENS
great or small. In fact the greater the central angle is, the more
acute become the outer angles. It is useful to remember that if
the number of degrees in all the three angles of a triangle be
added together, they are always equal to the number contained
FIG. 19. SINE OF ANGLE
in two right angles. That is, they always contain exactly 180
of arc.
The chord of an arc is of course shorter than the arc with
which it begins and ends. The smaller the angle, the less differ-
ence there is between the two, and in very small angles this
difference can be neglected, it is so minute.
The Greeks made great use of chords in their investigations.
Ptolemy, the astronomer (/. 127-151 A. D.), constructed tables
PROBLEMS IN CELESTIAL MEASUREMENTS 43
SHORE.
giving the length of both arcs and chords for every half-degree
up to two right angles.
THE SINE OF AN ANGLE
The Hindus, however, simplified their problems by taking
the chord of double the angle, and then cutting it in two and
discarding one half. The
half-chord used (A B) is
known as a sine of the angle
(A Z B) it measures (see
Figure 19).
The advantage of a sine
over a chord is this: In
solving problems in trigo-
nometry it is often conven-
ient to have one of the outer
angles a right angle, that is,
one containing 90 of arc.
Now, as the chord (A F) is
cut in the middle by the
bisecting radius (Z B), the
two lines always cross at
right angles (at B), and the
resulting triangle (A B Z) is
a right-angled one. The
result of one of the angles
being invariable is that part
of the labour is saved, as the
calculations are confined to
the other two angles. All
books on trigonometry have tables giving the length of sines,
etc., for every degree and fraction of a degree.
MEASURING INACCESSIBLE DISTANCES
The advantage of a right-angled triangle is shown in the fol-
lowing problem, which is something similar to one given in the
preceding chapter :
BASE
YDS'.
FIG. 20. MEASURING WIDTH OF
RIVER
44 HOW TO KNOW THE STARRY HEAVENS
A surveyor wishes to measure the width of a river without
crossing to the other side (see Figure 20).
First he measures off, on his own side of the river, a base-line
(A B) 10 yards long. He stands at one end (B) of his base-
line, and points his instrument at the other end of it (A). He
then turns the instrument one quarter round (90 of arc), and
selects an object (Z) on the opposite bank of the river. Having
made a note of the number of degrees he has turned the instru-
ment (90), he goes over to the other end (A) of the base-line
and repeats the operations. He will find that he will not have
to turn his instrument so far around to make it point to the
object selected (Z).
Let us suppose that he has to turn it only 89. The two
angles at the base will then together equal 179. Now, as the
three angles of a triangle, added together, always equal two
right angles (180), it is obvious that the opposite angle (Z)
must be just 1.
The problem then stands as follows :
As the sine of 1 (angle Z)
Is to the sine of 89 (angle A),
So is 10 yards (length of base A B)
To the perpendicular Z B (or Y).
After obtaining the length of the sines of 1 and 89 (which
are given in all books on trigonometry), the problem is solved
as follows :
As 01745 is to 99985, so is 10 yards to the answer, 573 yards,
which is the width of the river as exactly as it can be found
with five-place logarithms.
PARALLAX
The angle (Z) opposite the base of such a triangle is called
by surveyors and astronomers the parallax of the distant object.
The further off the object is, the smaller becomes its parallax.
PROBLEMS IN CELESTIAL MEASUREMENTS 45
The longer the base from which it is measured, the larger
becomes the parallax. 1
In the problem just considered it is obvious that if the object
Z is exactly west of the observer at B, it will no longer be ex-
actly west of him when he goes to A. It will be a little to the
south of west. It is also obvious that the amount of its displace-
ment will depend on its distance from him. The farther off the
object is, the less it is displaced when he goes from one end of
the base to the other. In other words, as stated before, the
more distant the object is, the smaller becomes its parallax. If it
is a very long way off, it may appear to be exactly west from both
ends of the base-line. In this case it will be necessary to greatly
lengthen the base-line in order to measure the distance of the
object.
The word " parallax " is rather a hard one to remember. But
astronomers can simplify matters when referring to the Sun's
parallax by calling it the " mean equatorial long horizontal solar
parallax." This is a useful thing to know.
A few examples of how astronomers utilize these principles
will conclude this chapter, which some may consider to be dryer
than a California summer, and more uninteresting than a
Baedeker's guide-book to one who never travels.
MEASURING THE MOON'S DISTANCE
We will of course start with the problem of finding the Moon's
distance from the Earth.
In Figure 21 the large circle represents a section of the Earth
through the two poles of rotation. The small circle in the dis-
tance represents the Moon. B and L are the two stations at the
ends of the measured base-line B L. We will imagine that they
are 4,000 miles apart, and that they are both on the same meri-
dian and at the same distance from the equator, which lies
between them.
1 " Parallax may be defined, generally, as the change produced in the apparent
place of an object when it is viewed from a point other than that of reference." -
ENCY. BRIT., Parallax.
46 HOW TO KNOW THE STARRY HEAVENS
Let us suppose that, to the observer at L, the Moon's centre is
exactly on the celestial equator, and is therefore exactly 90 from
the south pole (as well as from the north pole).
Then, to the observer at B, the Moon's centre will be found to
be 57 minutes of arc (nearly 1) south of the equator. That is
to say, it will be only 89 3' from the south pole, of which the
position is known even when it is out of sight. In the triangle
B L M, therefore, the angles B and L lack 57' of making two
FIG. 21. MEASURING DISTANCE OF MOON
right angles (180). This 57' is evidently the size of the other
angle M.
We have now a problem absolutely identical in principle with
the preceding one, which dealt with the width of a river. It
stands as follows:
As the sine of 51' (the angle M)
Is to the sine of 89 3' (the angle B),
So is 4,000 miles (the length of base B L)
To the perpendicular L M.
The problem is easily solved with almost the same figures as
in that dealing with the width of the river.
As 01658 is to 99986, so is 4,000 miles to 240,000 miles,
which is the approximate distance of the Moon at the time when
the angles were measured. 1
1 The above problem has been simplified as much as possible, so that the prin-
ciple may be readily grasped. As a matter of fact, the two ends of the base-line
PROBLEMS IN CELESTIAL MEASUREMENTS 47
For convenience of comparison, all results are reduced to fit a
right-angled triangle having a base-line equal to the radius, or
semi-diameter, of the Earth at the equator. The parallax is
then known as the horizontal equatorial parallax.
The distances of Mars and Eros are measured in the same
way as that of the Moon. But in the case of the Sun the
results have to be obtained by taking advantage of a transit of
Y
FIG. 22. ARC OF CIRCLE
Venus, or by some other indirect method. The principles and
results are, however, the same.
ARC PROBLEMS
The five following problems are worked out by means of two
radii and the enclosed arc (see Figure 22). The observer is
supposed to be at Z.
PROBLEM I. Given the angular diameter of Sun or Moon,
32' of arc (=1920" of arc), as seen from the Earth, find their
distances from us in terms of their own diameter A B (= 1).
are never exactly on the same meridian. Nor are they ever exactly the same dis-
tance north and south of the equator. And the distance required is not from the
Moon to the station L, but from the centre of the Moon to the centre of the Earth.
Quite a number of corrections and precautions have to be taken to give trust-
worthy results. But they need not be given here. It is sufficient if the principle
of the problem is thoroughly understood.
48 HOW TO KNOW THE STARRY HEAVENS
X 20fi 265"
2 A B = Y. Therefore l J 2(r A B = 107 A B.
[NOTE. For meaning of letters see the table at page 40.]
So that the distances of the Sun and Moon from the Earth are
both alike in terms of their diameters ; that is to say, the dis-
tance of each one of them is 107 times as great as its actual
diameter, whatever that may be.
This problem does not tell us how far they are from us or how
large they are. It merely proves that if the Sun (or Moon) is a
mile across, then it is 107 miles away from us ; while if it is
1,000,000 miles across, then it is 107,000,000 miles away.
PROBLEM II. Given the real distance of the Sun, 92,790,000
miles, and its angular diameter, 32' of arc (=1,920"), find its
real diameter in miles.
MILE$ MILKS
Z 1 920
^ Y = A B. Therefore ^265 92 > 790 > 000 = 863,727
The following form of this problem may perhaps be better
understood :
As X is to Z, so is Y to A B.
Worked out, this is as follows :
MILKS MILES
As 206,265" : 1,920" : : 92,790,000 : 863,727
PROBLEM III. Given the real distance of the Moon, 239,000
miles, and its angular diameter, 31' 6" (= 1,866"), find its real
diameter in miles.
This is a similar problem to the preceding one.
MILES MILES
rj 1 Q A A
= Y = A B. Therefore 2^265 239 > 000 = 2 > 162
Or, by the " rule of three " :
MILES MILES
As 206,265" : 1,866" : : 239,000 : 2,162
PROBLEMS IN CELESTIAL MEASUREMENTS 49
PROBLEM IV. Given the real diameter of the Sun, 863,727
miles, and its angular diameter 32' ( 1,920"), find its real dis-
tance in miles.
It will be seen that this is the reverse of Problem II.
MILES MILES
X 206,265
~ A B = Y. Therefore 863,727 = 92,790,000
Or, as before :
MILES MILKS
As 1,920" : 206,265" : : 863,727 : 92,790,000
PROBLEM V. Given the real diameter of the Moon, 2,162
miles, and its angular diameter, 31' 6" (= 1,866"), find its real
distance in miles.
It will be seen that this is the reverse of Problem III. It is
worked the same as Problem IV.
MILES MILES
^A B = Y. Therefore ^f|fjf 2,162 = 239,000
SINE PROBLEMS
The following problems are worked out by means of a right-
angled triangle constructed of two radii and the sine (or half-
chord) of the enclosed angle (see Figure 23 ; lettering same as
before).
PROBLEM VI. Given the Sun's distance, 92,790,000 miles,
and angular semi-diameter 16' (= 960"), find its real semi-
diameter in miles.
This is like Problem II, except that the semi-diameter is used
instead of the diameter.
MILKS MILES
Z 960"
Y Y = A B. Therefore 9nr 9r - 92,790,000 = 431,863
.A. ^UDj^OiJ
PROBLEM VII. Given the Moon's distance, 239,000 miles,
and its angular semi-diameter, 15' 33" (= 933"), find its real
semi-diameter in miles.
4
50 HOW TO KNOW THE STARRY HEAVENS
This is like Problem III, but uses the semi-diameter instead
of the diameter.
MILKS MILES
Z 933"
Y = A B. Therefore // 239,000 = 1,081
FIG. 23. SINE OF ANGLE
In all the following problems the observers are supposed to be
at A and B. Z is supposed to be the centre of the celestial body
under observation.
PROBLEM VIII. Given the Sun's parallax, 8.81", and the
Earth's semi-diameter, 3,963 miles, find the Sun's distance in
miles.
PROBLEMS IN CELESTIAL MEASUREMENTS 51
All solar and planetary parallaxes are for convenience reduced
to fit the semi-diameter of the Earth. This is here represented
by A B, and the parallax by the opposite angle Z.
MILES MILKS
X 206 265"
- A B = Y. Therefore 8 ' 8]// 3,963 = 92,790,000
PROBLEM IX. Given the Moon's parallax, 57' (= 3,420'%
and the Earth's semi-diameter, 3,963 miles, find the Moon's dis-
tance in miles.
This is a similar problem to the preceding one.
MILES MILES
X 206,265"
2~ A B = Y. Therefore 3 ^ 2Q , 3,963 = 239,000
Here is the same problem worked by logarithms, which must
be obtained from published tables of logarithms :
As the sine of 57' (angle Z) 8.21958
Is to base 3,963 miles (A B) 3.59802
So is sine of 89 3' (angle A) 9.99994
13.59796
8.21958
To perpendicular (Z B) 5.37838 = 239,000 miles
[NOTE. In small angles Z B = Y.]
PROBLEM X. Given the Sun's distance, 92,790,000 miles, and
the Earth's semi-diameter, 3,963 miles, find the Sun's parallax.
This is the reverse of Problem VIII.
4j? X = Z. Therefore ^fg^O 206 > 265 " = 8 ' 81
PROBLEM XI. Given the Moon's distance, 239,000 miles, and
the Earth's semi-diameter, 3,963 miles, find the Moon's parallax.
This is the reverse of Problem IX, and similar to Problem X,
52 HOW TO KNOW THE STARRY HEAVENS
A B 3,963
~~ X = Z. Therefore 206 > 265 " = 57 '
[If it is not too late, I would here suggest that those who do
not like Mathematics would do well to " skip " the foregoing
chapter.]
FIG. 24. SUN, SHOWING SPOTS AND FACUL^C
Photographed at Greenwich Observatory, Feb. 13, 1892.
V
CHAPTER V
THE CHARIOT OF IMAGINATION
" Before their eyes in sudden view appear
The secrets of the hoary deep ; a dark
Illimitable ocean, without bound,
Without dimension, where length, breadth, and height,
And time, and place, are lost." Milton, " Paradise Lost," Book IL
" Oh Deep, whose very silence stuns !
Where Light is powerless to illume,
Lost in immensities of gloom,
That dwarf to motes the flaring suns ! "
G. Sterling, " The Testimony of the Suns."
A LONG JOURNEY
TO enable us to realise, to some extent, what position man
holds with reference to the Universe, let us leave our
Earth for a short time, and hasten away, in the Chariot of Im-
agination, to a point in space half-way between our Sun and
Alpha Centauri, the nearest of the other stars.
We will take with us a specially constructed chronometer,
made to indicate long periods of time ; a special cyclometer, made
to fit the wheels of our chariot ; and a number of other scientific
instruments which may prove useful in our celestial researches.
In order that we may not get lost or have any corners to turn,
we make our start from Cape Town, South Africa, in the night-
time, when the Moon is above the horizon and Alpha Centauri
is on the meridian.
As this may be the first time some of us have travelled through
space unaccompanied by Mother Earth, it will be well for us to
travel slowly, so that we can get a good view of our surroundings,
and at the same time avoid running into unnecessary danger.
We will therefore keep a firm hand on the lines, from the start,
54 HOW TO KNOW THE STARRY HEAVENS
so as to prevent our imaginary steeds from running away with
us. On such a long journey the most satisfactory speed for us
to keep up will perhaps be that at which light travels, about
186,000 miles per second.
Everything being ready for our trip, the signal is given. " One,
two, three. Away we go I "
Before the words are fairly uttered, we find ourselves at the
Moon's distance and in the bright sunshine. By a curious
optical delusion we did not seem to move when the word was
given, but the moonlit Earth suddenly dropped from beneath
our feet. For a fraction of a second it appeared to swell, as dis-
tant lands and moonlit seas sprang above the horizon. Then
the Sun rose with a jerk, and the crescent Earth began to shrink
in size as its distance increased. 1
At the end of one minute the Earth is still plainly visible in
the bright sunlight, but the Moon is almost out of sight. In
five minutes nothing is to be seen of either of them.
For a time we are in the sunshine, but the light soon begins
to wane as we recede from the Sun and approach the confines of
the Solar System.
In four hours we are at the distance of Neptune, and the Sun
is not much more than a very brilliant star in the gathering
twilight.
Although the Sun continues to dwindle in size as we leave it
behind, it shines continuously, there being no horizon to hide it
from us. After we have been a month on our journey, as shown
by our chronometer, it is practically nothing but a bright star
among the multitude of stars by which we are entirely sur-
rounded.
By this time we have discovered that we have left behind
many things which seemed very real and important while we
remained on terra firma.
There is now no north or south, no up or down. The star-
1 For the above effects to be produced, we should really have to travel slower
than light, otherwise nothing would be visible in our rear. Every impossible
illustration has its discrepancies, as Artemus Ward would say,
THE CHARIOT OF IMAGINATION 55
sphere has ceased to turn on its axis, so that there are no pole
stars. The wandering planets have long- since disappeared.
There is no Sun or Moon. Day and night have ceased to roll.
Seed-time and harvest come no more. Summer and winter are
meaningless terms. Aside from our chronometer, months, years,
and centuries have now no significance. Away from our Earth,
geological periods trouble the mind no more.
We keep on in a straight line, at the same speed, for two long
years> as registered by our chronometer. The star which used
to be our Sun is now directly behind us, but has long ceased to
be conspicuous for either size or brilliancy.
And now the special cyclometer which we brought along tells
us that we are at last nearing our goal, the half-way house
between the centre of our system and the nearest outside star.
AMONG THE STARS
Arrived at our lonely destination, let us check our imaginary
horses, hitch them to an imaginary post, and take a survey of
our actual surroundings.
As we did not bring our Earth along with us, our view is not
impeded in a downward direction. We can see clearly below
and around, as well as above.
What is there to be seen from our point of vantage ?
One of the first things to attract our attention is that we do
not appear to have any immediate surroundings. We are soli-
tary in empty space.
Instead of being surrounded by houses and trees lighted up
by the dazzling glare of a hot Sun, or half-revealed by the soft
glamour of a pale Moon, we find ourselves alone in the midst of
perpetual starlight, which no Sun or Moon ever interferes with.
There is no cloud or fog, for all is cold, clear, still, dark, and
apparently void.
But in the far distance there are plenty of objects to make up
for an unoccupied " fore-space."
The " back-space " of sky is all more or less crowded with
stars. To the naked eye there are about 6,000 visible. These
56 HOW TO KNOW THE STARRY HEAVENS
are distributed promiscuously in irregular clusters and hap-
hazard groups, without any regard to pattern or symmetry.
But besides these groups of stars there are, in some parts of
the sky, great irregular streaks of nebulous haze. One set of
these hazy streaks is so long-drawn-out that its snake-like folds
and spirals almost form a girdle around us.
The unaided eye cannot pierce this haze, and without further
insight even the imagination itself is unable to invent a reason-
able explanation of this " Milky Way."
THE EYES OF SCIENCE
Let us now imagine that our eyes improve in light-grasping
power till they equal the most powerful telescopes in existence.
What is there now to be seen from our point of vantage ?
The result is something startling astounding overwhelm-
ing. The scene is grand beyond the power of language to
describe magnificent beyond the ability of the mind to
conceive.
The Earth we came from is still invisible lost in the depths
of infinite space.
The Sun that ruled our Solar System with such undisputed
sway is visible still, but it rules no more. It was a SUN that
reigned supreme among a thousand little twinkling stars. It is
now but a star among a hundred million fellow-stars.
But though we have lost our Earth and its Sun, we have
gained more than we have lost. For we have revealed before
us a goodly portion of the Universe itself. And though we
see no more a panoramic succession of days and nights, seasons
and years, we do not miss these earthly phenomena. For in their
stead we see the stately evolutions of countless squadrons of
heavenly orbs, circling through never-ending time in an ocean of
limitless space.
We have here no need of the Sun, neither of the Moon ; for
the everlasting glory of the Great Cosmos enlightens us, and the
iridescent mantle of Universal Nature enfolds us.
FIG. 26. - SOLAH FLAMES AND COHONA, AS SEEN DUKIXG ECLIPSK OF
MAY 28, 1900
By Burckhardt. (From Comstock's " Text-book of Astronomy,' 11 published by
Messrs. D. Applelon & Co.)
VTBRAT7
or THE
UNIVERSITY
or
JzALirCi*
THE CHARIOT OF IMAGINATION 57
On every side, above and below, we see stars by the million.
They are strewn through endless space like the blinding snow-
flakes of a Western blizzard. They are as thick as the leaves
of an earthly forest.
And we know that each and every star is a SUN, more or less
like unto our Sun. Many, if not all of them, have subject
worlds revolving around them like the planets which compose
our own system.
Gazing on such a picture, words are not equal to express our
sense of littleness. As the poet says :
This is a wondrous sight,
And mocks all human grandeur."
Contemplating the star-strewn heavens, the deist may well
exclaim with one of old
" When I contemplate the heavens,
The work of thy hands,
The Moon and the stars,
That thou hast disposed,
What is Man,
That thou shouldst remember him,
The Son of Man,
That' thou shouldst watch over him ? "
Ps. viii, 3 (Segond and Diodati).
The poet Shelley has beautifully described such a scene. He
says:
" Below lay stretched the Universe.
There, far as the remotest line
That bounds imagination's flight
Countless and unending orbs
In mazy motion intermingled,
Yet each fulfilled immutably
Eternal Nature's law.
Above, below, around,
The circling systems formed
A wilderness of harmony ;
Each with undeviating aim,
In eloquent silence, through the depths of space,
Pursued its wondrous way."
58 HOW TO KNOW THE STARRY HEAVENS
All around us is
" the abyss of an immense concave,
Radiant with million constellations, tinged
With shades of infinite colour."
A RUSH THROUGH SPACE
After having gazed for a while at the wonderful scene around
us? a scene so magnificent that even the words of a Saul among
the poets fail to give any adequate conception of it, we un-
hitch our imaginary horses from our imaginary post, turn our
Chariot of Imagination toward one of the stars, and rapidly
approach it.
ONLY A STAR
The star we selected for examination was a very ordinary-
looking star. It was far smaller than many of its neigh-
bours, and did [not shine anything like so brightly as some of
them.
But now that we have arrived in its vicinity it has grown in
size and brilliancy till all the other stars have either gone out
of sight or become faint dots of light, just perceptible in the
growing daylight. It has, indeed, become so overwhelmingly
radiant that we have to put on dark spectacles to enable us to
use our eyes without being blinded.
Let us stop and watch this star for a thousand years or so, and
see what changes are going on around it as it drifts along in the
ocean of space.
The star itself is a round yellowish-white ball more than
800,000 miles in diameter. Its glowing surface, or photosphere,
is one vast mass of shining cloud, which has the appearance of
being dotted all over with still brighter specks, like rice-grains.
This cloud-like photosphere is composed of calcium and other
elements, kept in a white-hot state by an unimaginably intense
heat rising from the gaseous interior of the star. The white
photosphere radiates into outer space about four times as much
FIG. 25. GROUP OF SUNSPOTS
Photographed with the Greenwich 26-inch Refractor, on Sept. 11, 1898. The largest
nucleus was about 24,000 miles long.
FIG. 27. ERUPTIVE PROMINENCES
Eclipse of May 28, 1900 (Barnard and Ritchey). The largest of these " hydrogen flames '
is 60,000 miles high.
THE CHARIOT OF IMAGINATION 59
light and heat as an electric arc-light of the same size would
do. 1
There are some peculiar features about this star as seen from
a short distance. Physical and mechanical reactions of incon-
ceivable violence are taking place beneath its surface. In some
places they give rise to what look like volcanic eruptions on a
vast and awe-inspiring scale. To an outside observer these
centres of eruption appear like great irregular black blotches
scattered about the white cloud-like photosphere. They are sur-
rounded by plume-like shadows or penumbrae. By watching
these black spots we soon find that the star is spinning slowly
around on its axis, completing a revolution in about twenty-seven
of our days.
The light given out by this white photosphere is so dazzling
that little more can be made out, even with dark glasses. We will
therefore use special instruments to turn it aside, so as to enable
us to see more clearly what other phenomena are going on in
the neighbourhood.
We can now see that the entire body of the star is buried
under a shoreless ocean of transparent fire of a scarlet hue. This
fiery ocean, or atmosphere, is everywhere from 4,000 to 5,000
miles deep, and appears to rest on the white cloud-like photo-
sphere already described. The storm-tossed surface of this fiery
ocean bristles at every point with huge ascending " flames " of the
same scarlet colour. Those on our side of the star are not readily
examined, on account of the brilliancy of the photosphere, but
those around the edges are plainly visible with proper apparatus.
Most of them are about 8,000 or 10,000 miles high, but here and
there are larger ones, reaching up 60,000 miles or more. These
huge ruddy flames assume a great variety of forms. They re-
semble jets of steam, fireworks, fountains, ocean breakers, cy-
clones, torpedo explosions, and volcanic eruptions, all on a scale
of inconceivable magnitude.'
1 By the way, an electric arc-light the size of a pin's head cannot be examined
without the aid of dark glasses, it is so overwhelmingly bright. And its tempera-
ture is 6,300 F. But this star is nearly a million miles through and is very
much brighter and hotter !
60 HOW TO KNOW THE STARRY HEAVENS
As we watch this stormy scene it reminds us of a wind-tossed
prairie fire as seen by night through a telescope on our little
Earth. The flames rise and dart forward, fall back and roll
over ; bend, twist, and curl ; embrace, wrestle, and fling them-
selves apart. Before our eyes they change into all imaginable
shapes, so that we find it almost impossible to realise their over-
whelming magnitudes and the terrific speed of their varied
movements. Every once in a while we see great ruddy blasts
of fiery gas rise from the surface with tremendous force and in-
conceivable velocity. Some of these flaming jets shoot up at
the rate of 250 miles in a second of time, and reach an altitude
of 200,000 or 300,000 miles. They then branch out in tree-like
clouds, and finally break up and scatter in a shower of solar
fireworks. The very largest of these flames are long enough to
be wrapped sixteen times around our Earth.
These ruddy flames (though cooler than the white photosphere
beneath them) are so inconceivably hot that they do not burn.
In fact they would " unburn " any burnt substance which might
fall into them, even if it should happen to be as large and heavy
as our Earth. No chemical compound could exist for a second
in such a terrific heat. No element, even, could remain there in
a solid or liquid state. The flames are composed of incandescent
hydrogen and helium, while the ruddy sea from which they rise
contains also iron, magnesium, sodium, and other metals, all
vaporised by the tremendous heat.
This scarlet ocean of fiery gas is termed a sierra or chromo-
sphere. The flames which rise from it are known as prom-
inences.
Outside of all these is a corona, consisting of great hazy radi-
ating streaks of some light and apparently gaseous substance,
extending a million miles or more into outer space. Owing to
their distribution, and to the fact that the star is spinning
around on its axis, these " repulsive " streaks are not straight,
but slightly curved, and have a very peculiar plume-like
appearance.
FIG. 28. SOLAR CORONA. ECLIPSE OF MAY 28, 1900
Photographed by Chabot-Dolbeer Eclipse Expedition.
FIG. 29. XOKTH POLAR STREAMERS OF THE CORONA. MAY 28, 1900
Crocker Eclipse Expedition.
THE CHARIOT OF IMAGINATION 61
OFFSPRING OF A STAR
As we watch the eruptive " freckles " which come and go every
eleven years on the surface of the star, we notice a number of
small balls sweeping around and around it, all going in the same
general direction. These are all worlds, more or less like the
one on which we used to live before we began our heavenly
wanderings. Let us watch them as they eddy around the star,
like moths circling around a lantern in the dark.
THREE CLASSES OF WORLDS
The most noticeable of them are four outer or superior planets.
These are so much larger and more powerful than the rest that
they form a kind of aristocracy, subject only to the reigning
monarch in the centre. They do not appear to shine by their
own light, yet they are still puffed up with heat. They have
followers, or satellites, of their own, so that they are something
like petty rulers subject to a higher power.
Four very insignificant planets form an inner or inferior family
of worlds. They give out neither light nor heat of their own,
so they may be called terrestrial planets. They are much more
under the control of the central ruler, but at the same time may
be said to bask in the sunshine of his favour. They are, in fact,
the bourgeoisie or well-to-do citizens of the monarchy.
Between these two families of worlds there is a whole regiment
of almost invisible planets, which may be called asteroids, from
their small size and star-like appearance. They are the pro-
letarians, the working-class of the monarchy, subject not only to
the legitimate rule of the sovereign, but also to the overbearing
authority of the aristocracy on the one hand, and to the petty
bossing of the bourgeoisie on the other. They are in fact " be-
tween the upper and the nether millstone." The result is shown
by the steep, elongated, and apparently dangerous paths some of
them are compelled to follow, with neither hope of relief nor
promise of reward.
62 HOW TO KNOW THE STARRY HEAVENS
Although the four outer planets appear to us to be very large,
yet they are extremely small compared with the central star,
which is 560 times as large and 745 times as heavy as all the
planets put together.
Let us now examine some of the individuals composing these
three classes of worlds, beginning with the inner planets.
THE INNER PLANETS
The one which is nearest to the central star is small, and very
little can be seen of it. The second is larger, with a dense atmos-
phere which somewhat obscures the planet itself. Both of these
little wgrlds move at a speed many times greater than that of a
cannon-ball, yet it takes them several months to go once around
the central star.
PLANET NUMBER THREE
Planet No. 3 is slightly larger than No. 2, its diameter being
nearly 8,000 miles. It is, indeed, the largest of the inner family
of worlds. It is more than 90,000,000 miles from the star
around which it is sweeping. It takes just a year to complete a
revolution, although it travels at the astounding rate of eighteen
miles in a second of time.
On looking more closely at this world, another and smaller
planet is seen buzzing around and around it. This is a moon or
satellite, which goes around its primary in the same direction as
that is going around the central star. It is a little over 2,000
miles thick, so that the principal planet is about fifty times as
large as its companion.
A more attentive look at No. 3 reveals several peculiarities.
It is spinning around like a top, turning in the same gen-
eral direction as that in which it goes around the central star.
The two points which form its poles of rotation are white, as
though covered with ice and snow. Its surface is variegated,
and is evidently composed of land and water. There are con-
tinents, oceans, islands, seas, lakes, rivers, and mountains. The
land appears to be more or less covered by vegetation of a green
FIG. 30. MERCURY-, THE FIRST PLANET
By Schiaparelli. (From Todd's " Stars and Telescopes," published by Messrs. Little, Brown, <fe Co. )
FIG. 31. VENUS, THE SECOND PLANET
By Autoniadi. (From Comstock's " Text-book of Astronomy," published by
Messrs. D. Appleton & Co.)
FIG. 33. MARS, THE FOURTH PLANET
By Knobel. (From Todd's " Stars and Telescopes," published by Messrs. Little, Brown, & Co.)
THE CHARIOT OF IMAGINATION 63
colour, while portions of the surface are hidden by drifting
clouds. Altogether, it looks like a world which might be in-
habited. Although small compared with the giant planets
which circle on the outskirts of the system, yet the diversity of
its surface, and the terrific speed with which it circles around
FIG. 32. TERRA, THE THIRD PLANET, AND ITS SATELLITE
OR MOON
the central star, entitle it to the archangel's song as given in the
prologue to Goethe's " Faust " :
" And swift and swift beyond conceiving,
The splendour of the World goes round,
Day's Eden-brightness still relieving
The awful night's intense profound.
The ocean tides in foam are breaking,
Against the rock's deep bases hurled,
And both, the spheric race partaking,
Eternal, swift, are onward whirled."
Bayard Taylor's Translation.
PLANET NUMBER FOUR
Planet No. 4 has a ruddy appearance. It is considerably
smaller than the one just described, its diameter being only
about 4,000 miles. It has two very small moons circling around
it. Like No. 3, it has the appearance of being in a condition
suitable for sustaining life. It appears to have an atmosphere,
clouds, and variegated continents. Its poles, too, are white, as
though covered by ice and snow.
64 HOW TO KNOW THE STARRY HEAVENS
PLANETOIDS
After Planet No. 4 there is a great crowd of little worlds
which are too small to be of much importance. The most in-
teresting thing about them is the speculation whether or not
they are the fragments of
two larger planets that
have unsuccessfully tried
to occupy the same space
MA us at the same time.
A GIANT PLANET
Outside this swarm of
pigmy worlds there circles
and spins a gigantic ball
about 1,200 times the size
of Planet No. 3. It is not
only the largest of all the
planets, but is larger than
all the rest of them put
together. It has a dense
impenetrable atmosphere,
with bands of clouds around
its equatorial regions.
There are five moons sweep-
ing around it, some of them
being of considerable size,
far larger than any of the
planetoids just mentioned.
The main planet, although
so large, spins around in a little less than ten hours. This rapid
rotation has made its equator bulge out, so that the cloud-like
surface of the planet is something the shape of an orange.
A RINGED PLANET
After this there is another big globe, only second in size to
the one just described. But this one is surrounded by such an
FIG. 34. RELATIVE SIZES OF EARTH
AND MARS
FIG. 35. THE ZONE OF ASTEROIDS BETWEEN MARS AND JUPITEU
FIG. 36. JUPITER, THE LARGEST I'LANET
Showing great red spot and transit of satellite. Lick Observatory.
THE CHARIOT OF IMAGINATION
65
astonishing arrangement that one cannot help rubbing his eyes
to see if they have not deceived him. It looks as though there
was a large round thin disc, with a good-sized round hole in the
middle. In the centre of this hole is the planet itself, not quite
large enough to fill the hole, and not visibly connected with
the disc. On a closer view the disc is seen to have a series of
gaps and thin places in it,
extending all around, as
though it were really a
series of discs all lying in
the same plane, and hav-
ing the planet for a centre,
but differing in size and
texture. If these concen-
tric discs or rings were
visibly supported by the
planet, they would not
seem so extraordinary,
but the closest scrutiny
fails to discover any phy-
sical connection with the
globe they surround. The
only explanation that
seems able to account for
their continued existence
is that they are composed
of countless millions of
tiny satellites crowded
together, and revolving around the planet in the same direction. 1
Farther off than these rings there are nine satellites, or
moons, revolving at different distances from the planet. The
whole family group seems almost a miniature of the solar sys-
tem of which it forms a part, with a hint thrown in as to how
that system originated.
1 If they were farther from the planet, they would probably coalesce into
regular satellites, but as it is, the tidal action of the huge planet prevents
this. 5
FIG. 37. RELATIVE SIZES OF JUPITER
AND EAKTH
66 HOW TO KNOW THE STARRY HEAVENS
TWO OUTER PLANETS
There are two more large planets outside the one just described.
But they are not so remarkable in appearance, and they are so far
from the central star that they are comparatively in the cold and
dark. The outside one is about 30 times as far off as Planet
No. 3, and is 125 times as large. It moves only a little
over three miles in a second of time, and, as it has a large
circuit to make, it takes 164 years to go once around the
central star.
It is interesting to
note that the combined
mass of the four out-
side planets just men-
tioned is about 220
times as great as the
combined mass of the
four inner planets, with
.all the visible planet-
oids thrown in. Also
that the same outside
planets together weigh
450 times as much as
No. 3 alone. If only
bulk and mass were
concerned, it would 'scarcely be worth while to mention the
inner planets at all, they are so insignificant.
SOLAR SYSTEM No. 3,141,592,653
It is hardly necessary to explain that the star we have been
examining, with its attendant worlds, forms our own Solar Sys-
tem. The insignificant little globe which I have called " Planet
No. 3 " is our own World, once regarded, by its reasoning inhab-
itants, as the whole Universe, with nothing outside but the
Realms of Chaos.
If we were to approach any one of the millions upon millions
of sovereign suns revealed by the telescope, we should in all
FIG.
). RELATIVE SIZES OF SATURN
AND EARTH
H
W
I I
THE CHARIOT OF IMAGINATION
67
probability find it to be the centre of a family group more or
less similar to ours. Some systems are smaller, but others are
far larger, while many are more elaborate and democratic, with
two, three, four, a hundred, or a thousand suns circling around
their common centre of gravity.
FIG. 40. RELATIVE SIZES OF NEPTUNE
AND EARTH
CHAPTER VI
DIMENSIONS OE THE UNIVERSE
"Firstly, we may inquire as to the extent of the Universe of stars. Are the
latter scattered through infinite space, so that those we see are merely that por-
tion of an infinite collection which happens to be within reach of our telescopes,
or are all the stars contained within a certain limited space ? "
Prof. Simon Newcorrib.
PLANETARY DISTANCES
IN the third and fourth chapters I tried to show the principles
by which the distances of the heavenly bodies are measured.
It was there stated that the Moon's distance from us is about
239,000 miles, and that the Sun is about 388 times as far off.
The most reliable measurements make the Earth's distance from
the Sun 92,790,000 miles. Neptune, the farthest planet in our
system, is about 30 times as far from the Sun as we are, so that
it is 2,790,000,000 miles away.
This distance is so tremendous that it is unthinkable. The
mind of man cannot grasp it. It is as utterly beyond our com-
prehension as infinity itself. Yet when we turn to the stars we
find that this vast distance is as nothing when compared to the
intervals separating one star from another.
STELLAR DISTANCES
It has been ascertained that the nearest star outside our sys-
tem is something like 9,000 times as far off as Neptune, whose
distance seemed so amazingly great. Alpha Centauri, the nearest
of all the stars, is distant from us about 25,000,000,000,000
miles. Its light, travelling at the rate of 186,000 miles in a
second of time, takes more than four years to come to us.
The brightest star in all the sky is known as Sirius, or the
Dog Star. It is twice as far from us as Alpha Centauri, and is
therefore more than eight "light-years " away.
DIMENSIONS OF THE UNIVERSE 69
The distances of about sixty other stars, ranging up to sixty
light-years, have been more or less approximately ascertained.
All the others are too far off for our sounding-rods. They are out
of reach in the depths of space. All that we know for certain
concerning their distances is that none of them are less than
4,000,000 times as far from us as our Sun, which is nearly
93,000,000 miles away. 1
COMPARISONS
Now it is very easy to say that the nearest star outside our
system is 25,000,000,000,000 miles away, but it is not so easy
to realise what that distance is like. Let us try to do so by
means of some simple illustrations.
In the first place it is necessary to realise the proportionate
distances and dimensions of the members of our own Solar
System.
If we take a one-inch ball to represent our Earth, it will
require a nine-foot globe to represent the Sun.
Let us place this nine-foot globe on a level plain that has
just had the grass burnt off it, and set up wire circles (on posts)
to indicate the various planetary orbits.
The sizes of the planets and the distances of their orbits from
the central globe will be as follows :
PLANET
Mercury .
Venus
Earth . .
Mars . .
Asteroids
Jupiter . .
Saturn .
Uranus .
Neptune .
1 Investigations are now in progress which promise greatly to extend the list
of stars having a measurable parallax. It is possible that the distances of most of
the naked-eye, stars will be ascertained before many years have passed.
SIZE
DISTANCE
large pea .
127 yards
one-inch ball
235 "
one-inch ball
325 "
half-inch marble .
495 "
small seeds
676 "
1,385 "
eleven-inch globe
1 mile (nearly)
nine-inch globe .
If miles
four-inch globe .
3 "
five-inch globe .
5 '<
70 HOW TO KNOW THE STARRY HEAVENS
On this scale our Moon will be represented by a pea moving
in a circle at a distance of 30 inches from the one-inch ball
representing the Earth.
The outside ring of Saturn will be 21 inches in diameter.
The orbit of Neptune will be 11 miles across, and will take
nearly 35 miles of wire to mark it out.
Let us now make arrangements with an electric light com-
pany to cover our nine- foot globe with a complete network of
electric lights, so close and compact that every part of the sur-
face will give off more light and heat than the brightest part of
an arc-light. We will then choose a dark yet clear night, and
turn on the current.
We shall find that all of our toy planets are more or less bril-
liantly illuminated on one side by the central light. But of
course the outer side of each " planet " will be dark and invis-
ible. Let us station ourselves just beneath the one-inch ball
which represents our Earth, and take a look around at our
miniature "solar system."
The overpowering effulgence of the nine-foot globe, 325 yards
away, makes it necessary for us to put up a shelter to protect us
from the light and heat.
Apart from our electric " sun," the most prominent object
visible from our position will be the quarter-inch ball which goes
around us at a distance of 30 inches. It will, in fact, look as large
as our nine-foot " sun," but will not be anything like as bright.
As the illuminated side of this imitation " moon " does not
always face us, it will show all the phases of the real Moon as
it goes around in its little orbit.
The first of our toy planets (that is, the one nearest to the
central globe) will be just visible to us when most favourably
placed. The second will shine very brightly when it is at a
large angle from our "sun." Both of these toy planets will
show lunar phases if examined with the help of a telescope.
The fourth " planet " (half an inch in diameter), will also be
very brilliant when at its nearest, 170 yards away. But at
other times it will be rather inconspicuous.
FIG. 41. LICK OBSERVATORY ON MOUNT HAMILTON, CALIFORNIA
FIG. 42. MAIN ENTRANCE AND GREAT DOME, LICK OBSERVATORY
DIMENSIONS OF THE UNIVERSE 71
The first and second of the large planets will also be tolerably
conspicuous, although a telescope will be necessary to show
details.
The two outside planets will not be visible at all without a
telescope. The farthest of them will not vary much in appear-
ance ; its distance at all parts of its orbit being something like
5 J miles away from us.
The nearest star will, on the same scale, be represented by an
electric globe, probably 12 feet across, at a distance of about
50,000 miles. Sirius will take a similar globe, nearly 30 feet in
diameter, about 100,000 miles away. The largest star visible
to us may probably be represented by a 100-foot globe, some-
where about 1,000,000 miles distant.
This illustration gives a fair idea of the comparative dimen-
sions and distances of the principal bodies forming our Solar
System, but fails to convey any definite idea of stellar distances.
Let us try some other illustrations.
A LOCOMOTIVE
We all know what it is to travel at the rate of 60 miles an
hour. At this rate it would take 17 J days and nights to travel
around our own world.
To reach the Moon, travelling at the same rate, it would take
166 days, or nearly half a year.
To reach the Sun, we should have to travel for 176 years.
To go around the Sun would take about 5 years.
To go from the Sun to Neptune, the farthest planet, would
take 5,000 years, and the railway fare, at one cent a mile, would
be nearly $28,000,000. This makes a railroad impracticable.
A CANNON-BALL
Now take a cannon-ball travelling at the rate of a mile in five
seconds.
It would go around the Earth in 36 hours, and would reach
the Moon in 14 days.
72 HOW TO KNOW THE STARRY HEAVENS
To get to the Sun would take it 1 5 years, and it would require
5 months to go around it. To go from the Sun to Neptune, the
farthest planet, it would have to travel at the same speed for
415 years.
AN ARROW OF LIGHT
A wave of light travels at the enormous velocity of 186,000
miles in one second of time. So it would go around our Earth
more than seven times in a second. It would reach the Moon
in a second and a quarter.
It takes more than eight minutes for the Sun's light to reach
us, and over four hours for it to get to Neptune, the outside
planet in our own system.
At the same rate, 186,000 miles a second, it takes more than
four years for the light of the nearest star to reach us.
Sirius, the brightest star in the sky, is so far off that the light
which reaches us to-night has been eight and a half years on the
way. If it were to collide with another star now, we should not
see the flare-up for eight years and a half. 1
A PILE OF PAPER
Now, suppose that we had here a pile of thin paper, with as
many sheets in it as there are miles between us and the nearest
star. What would be the height of the pile, supposing that it
took 200 sheets to measure one inch in thickness ?
Those people who are naturally reasonable in their ideas and
moderate in their estimates might think that the pile would
probably be a hundred feet or so in thickness. Others, who are
naturally wild in their ideas and extravagant in their guesses,
would think that the pile might possibly be a mile thick. As a
matter of fact, it would reach up nearly 2,000,000 miles. More
exactly, its height would be 1,972,853 miles, 94% yards, and 8
inches.
1 The distance of Sirius is not less than that stated, but there is a possibility
that it is greater.
FIG. 43. THE THIRTY-SIX-IXCH REFRACTOR AT LICK OBSERVATORY
The tube is 5G feet long and weighs several tons. It is equatorially mounted, with a
driving clock. The entire floor under the dome can be raised or
lowered 26 feet. It is shown half-way down.
DIMENSIONS OF THE UNIVERSE 75
As this pile of paper is rather top-heavy, suppose we lay it
down on its side. Then it will go nearly 79 times round the
Earth. Yet every inch in this great pile of paper represents a
distance of 200 miles. The sheets would have to be placed a
mile apart before they would reach to the nearest star.
A STACK OF BLOOD DISCS
Perhaps a smaller illustration of the same kind may be more
within our mental grasp.
Human blood is an almost colourless fluid, crowded with very
small red discs or corpuscles. These discs are flat and coin-
shaped. They are so extremely minute that if they were piled
up one on the top of another, like a stack of coins, it would take
15,000 of them to reach one inch in height.
If we let each disc stand for one mile, then the height of the
pile representing the Moon's distance will be 16 inches. That
representing the Sun's distance will reach up 172 yards, and
Neptune's pile will be nearly three miles high. But the pile
which contains as many discs as there are miles between us and
the nearest star will be 26,000 miles in height. If it were laid
down on the ground it would go around the world.
VIOLET WAVES
The shortest light-waves which affect the eye are those which
produce the sensation of violet light. It takes 61,000 of these
waves to measure one inch. If a single wave stands for a mile,
then the distance of the Moon will be represented by 4 inches ;
of the Sun, by 42 yards ; of Neptune, by 1,250 yards ; and of
Alpha Centauri, by 6,400 miles.
Then we must remember that the vast majority of even naked-
eye stars are hundreds and thousands of times farther off than
the one we have been considering.
A LONG STRAND
The cotton factories of Lancashire, England, at present spin
about 155,000,000 miles of thread in a day, so that in six seconds
74 HOW TO KNOW THE STARRY HEAVENS
they make enough to go around the Earth. In one minute they
spin enough to reach from here to the Moon. The product of
18 days would reach from the Sun to Neptune. Counting 310
working days in a year, it would take them, at this rate, 500
years to spin enough thread to reach to the nearest star.
If one end of this thread were to be made fast to some place
on our equator, the daily rotation of the Earth would wind up
25,000 miles of it every day. At this rate it would take about
300 years to wind up that part of the thread between us and
Neptune. But to wind up the whole of the thread between us
and the nearest star would take ,500,000 years.
Let us suppose that this thread is all wound around the Earth,
and that the size of the thread is such that a rope of it an inch in
diameter contains 10,000 threads. Then the entire skein would
make a rope nearly 26 feet in diameter around the entire Earth.
Let us suppose that four miles of this thread weighs one
pound. Then that part of it between the Sun and Neptune will
weigh 340,000 American tons. And the same-sized thread
reaching to the nearest star will weigh -3,000,000,000 American
tons. If twenty tons of it were to be loaded on one railroad car, it
would take 17,000 cars to carry that part between the Sun and
Neptune, and the thread reaching to the nearest star would take
150,000,000 cars to hold it all.
A SPIDER'S THREAD
These numbers are still too large to be realised by the human
mind as at present constituted. Fortunately, however, there is
a way of considerably reducing them.
The thread spun by some spiders is so extremely fine and light
that a single pound of it would be long enough to reach around
our Eai\h. Let us see if we cannot get more reasonable weights
by using this light and invisible thread.
To reach to our Moon would require nearly 10 pounds of it.
To go to the Sun would take 3,712 pounds. Neptune's distance
would require 56 American tons of it.
FIG. 44. EYE-PIECE OF THE GREAT LICK TELESCOPE
DIMENSIONS OF THE UNIVERSE 75
But to reach to the nearest star would take 500,000 tons.
At twenty tons to the car, this would take 25,000 cars to carry
it all. At 35 feet to the car, these would make a train of cars
167 miles in length. This train would require 500 powerful
locomotives to move it.
A QUARTZ FIBRE
We can get still better results by taking a quartz fibre like
those used in a torsion-balance for weighing the Earth. They
can be made one-hundred-thousandth of an inch in diameter,
with tapering ends which thin off to the millionth of an inch.
No microscope can show a fibre of this latter size, but its presence
can be made apparent by means of photography. Nine and a
half grains of this invisible quartz fibre (equal to one seventieth
of a cubic inch) would reach to the Moon. Half a pound of it
would go nearly to the Sun. Sixteen pounds would reach to
Neptune. But it would take 72 American tons (equal to a cube
of 9 feet 4 inches) to go to Alpha Centauri.
ONE CENT A MILE
If a railroad could be constructed to the nearest star, and the
fare made one cent a mile, a single passage would cost $860000-
000,000. This would make a 94-foot cube of pure gold. The
coined gold in the world amounts to $4,000,000,000, about equal
to a 24-foot cube. It would therefore take more than 60 times
the world's stock of coined gold to pay the fare of one passenger.
Let us save up our money and go when the line is built !
A TIRELESS WHEEL
One more illustration will bring this chapter to a close.
Let us suppose a wheel to be turned at the speed of 100 revolu-
tions in a second of time. This is equal to 6,000 times in a minute.
At that speed it will go around 1,000,000 times in a little less
than three hours. To go around as many times as there are
miles between us and the Sun would take nearly eleven days.
To go around as many times as there are miles between the Sun
76 HOW TO KNOW THE STARRY HEAVENS
and Neptune, the outside planet, would take nearly eleven
months. But to go around as many times as there are miles
between us and the nearest star outside our system would take
nearly 8,000 years.
These comparisons will do for the present. Let us take a rest
till the next chapter.
CHAPTER VII
SOME MORE DIMENSIONS
" That collection of stars which we call the UnfVerse is limited in extent.
. . . This does not preclude the possibility that far outside of our Universe there
may be other collections of stars of which we know nothing."
Prof. Simon Newcomb.
" Then the angel threw up his glorious hands to the Heaven of Heavens, say-
ing : ' End is there none to the Universe of God. Lo, also, there is no begin-
ning ! ' " De Quincey.
A LONG SHEET OF PAPER
AYEEY good way to get an idea of the relative distances
of the heavenly bodies is to mark them off, on a small
scale, on a long sheet of paper.
In order to do this properly, get a 1,000-pound roll of paper,
like that on which magazines are printed. 1 Set up a bench or
table, about 4 miles long, and unroll the paper on it. Draw
a straight line down the middle of it, from one end to the
other. We can now choose a unit of measure, and mark off
the distances along this line.
Let us make a mark to represent the Sun, and another, one
inch away, to represent the Earth. Then one inch will stand
for 93,000,000 miles. On the same scale, Mars, the ruddy
planet, will be \\ inches off; Jupiter, the largest of the planets,
will be 9^ inches distant; Uranus will be 19 inches off; and
Neptune, the farthest of all the planets, will be 30 inches
away. 2 The distance that light will travel in one year will be
1 Such a roll is 20,250 feet long and 39 inches wide.
2 The orbits of all the principal planets are on nearly the same plane. There-
fore, on the above scale, the Solar System could be contained inside a round disc
of wood five feet in diameter and two inches thick. Very few even of the small
planets (asteroids) would ever go outside of this thin disc.
78 HOW TO KNOW THE STARRY HEAVENS
represented by one mile. The nearest star, on the same scale
of one inch to the Sun's distance, will be more than four miles
away. And Sirius will be eight and a half miles distant.
But stay ! Our long sheet of paper is too short. Let us
erase these marks and try a smaller scale.
In order to get the most convenient unit, measure off a 12-
inch line and divide it into ten equal parts. Then divide one
of these parts also into ten. This will give us the one hundredth
of a foot for a unit. -We may regard it as equal to one eighth of
an inch, although it is really a trifle shorter.
If we make this little unit represent a mile, the distance of
our Moon from us will be represented by 800 yards. It is quite
evident that this scale is too large for our purpose. We must
choose a smaller one.
As our Moon is nearer to us than any of the other heavenly
bodies, we will let our little unit represent the Moon's distance.
First, make a mark, to represent the Sun, at one end of our
long sheet of paper. Then put another mark, nearly four feet
away, to stand for the Earth, with a quarter-inch circle around
it to represent the Moon's orbit. Neptune's place may now be
marked out, at a distance of 117 feet from our starting-point.
The position of the nearest star will be about 200 miles far-
ther on.
As our paper is again too short, we will reduce the scale, and
regard our unit as representing the distance of the Earth from
the Sun. Then Neptune's distance will be 3| inches, and that
of Alpha Centauri will be 900 yards.
Even this small scale is too large for some of the star-dis-
tances which have been approximately ascertained. So we will
try again. This time we will represent the distance of Neptune
from the Sun by our unit, so that the entire Solar System will
be about the size of a pea. Every eighth of an inch will thus
represent 2,790,000,000 miles!
At last we have succeeded in our efforts to get some of the
stars on to our paper. The distance of Alpha Centauri will on
this scale be only 90 feet. Sirius, the brightest star in the
SOME MORE DIMENSIONS 79
heavens, will on the same scale be represented by a microscopic
grain of sand- 180 feet away, yet glaring with such an over-
whelming intensity of light as sometimes to throw shadows on
the invisible point which represents the Earth.
The great majority of the visible stars, however, on the above
scale of one eighth of an inch to the distance of Neptune, will
be scores and hundreds of miles away. So that we shall have
to try some other way of visibly representing their distances.
SOME BIG SQUARES
If, instead of using a straight line on which to represent
distances, we use different-sized squares for the same purpose,
we shall perhaps be more successful in appealing to the eye.
Take a square piece of white pasteboard which measures a
foot each way. On each edge mark off ten equal divisions.
Then with pencil and ruler join the opposite marks, thus
making a kind of chess-board with 100 equal squares. In the
same way divide up one of these squares into 100 equal squares.
Each of these smaller squares will be nearly one eighth of an
inch across.
Taking one of these tiny squares^ as a unit (1), the whole
square will contain one hundred units (100), and the entire
pasteboard will be equal to ten thousand units (10,000).
Now if each of these little squares or units be made to repre-
sent one mile, it will take a square nearly five feet across to
represent the distance of the Moon from the Earth. To repre-
sent the Sun's distance from us, it will take a chess-board meas-
uring 96 feet each way. Neptune's distance will be represented
by a square measuring 525 feet. The distance of the nearest
star will take a chess-board measuring 9 J miles each way, and
covering 90 square miles of land. It must be remembered that,
on this scale, every eighth-of-an-inch square of surface represents
a mile between us and the nearest star.
It is evident that we shall have to try a smaller scale if we
are to make the stellar distances visible to the eye by means of
squares. If we let one of the tiny squares represent the distance
80 HOW TO KNOW THE STARRY HEAVENS
between us and the. Sun, then the distance of the nearest star
will be represented by a chess-board more than five feet in
diameter.
If we reduce the scale still more, and make our unit represent
the distance of Neptune from the Sun, then the distance of
Alpha Centauri will be represented by nine tenths of our 12-
inch chess-board.
SOME SOLID COMPARISONS
In order to bring our measures still more within the reach of
the eye, the little unit just used may be cubed. It will then be
a solid block, measuring nearly one eighth of an inch every ^way.
Kegarding this cube as the equivalent of a mile, the Moon's
distance will be represented by a 7J-inch cube. The Sun's dis-
tance will take a cube 4 feet 6 inches every way, and Neptune's
will take a 14-foot cube. The distance of Alpha Centauri will
be represented by a cube measuring 290 feet every way.
A GREAT VOID
Let us now consider in other ways the vastness of this appar-
ently empty space between our system and the nearest star.
Make a circle, two inches across, on the ground. Let this
circle represent our entire Solar System, with the Sun in the
centre. Then a similar circle including the nearest star will,
on the same scale, be 1,524 feet across. That is to say, it will
make a circular race-track nearly a mile around.
If these circles be regarded as solid spheres or globes, then
the larger one, representing the intense loneliness of our Solar
System, will be equal to 766,000,000,000 globes like the smaller
one that represents the size of our system.
LONG-RANGE CANNON
It is difficult for one who is not an astronomer to realise the
enormous light-grasping power of our great telescopes. Most of
us, indeed, fail to realise even the power of the unaided eye to
penetrate space. Here are a few illustrations of both.
FIG. 45. YERKES OBSERVATOKT, WILLIAMS BAY, WISCONSIN
FIG. 46. THE FORTY-INCH REFRACTOR OF THE YERKES OBSERVATORY:
THE LARGEST IN THE WORLD
SOME MORE DIMENSIONS 81
Suppose that our Sun were to leave us and go off in the direc-
tion of Sirius at such a rate as to double its distance in one
year. And suppose it were to continue receding at the same
rate for an indefinite period. In 100,000 years it would be about
as bright as Sirius, though the latter would still be 5| times as
far away from us. In 550,000 years it would pass Sirius and
appear to us about as bright as the Pole Star. In 3,000,000
years it would be just visible to the naked eye, and its light
would take 46 years to reach us. After receding for 750,000,000
years, it would still be visible to a telescope with a 50-inch ob-
ject-glass or mirror, and its light would take more than 11,000
years to reach us.
Suppose that Sirius were to recede from us at the rate of
1,500,000 miles per second (eight times the speed of light), so as
to double its distance in one year. In 30 years it would be just
visible to the naked eye, and its light would take 240 years to
reach us. After receding for 7,500 years it would still be visible
with a 50-inch telescope, and its light would take about 60,000
years to reach us. 1
Suppose that a star that is just visible to the naked eye were
to recede from us at such an inconceivable rate as to double its
distance in a year. It would be about 250 years before it would
be lost sight of by the same 50-inch telescope. 2
Let one inch represent the distance of the farthest star visible
to the naked eye. Then the distance at which our largest tele-
scopes would lose sight of it will be represented by about 21
feet.
This last illustration may be put in another form. If a globe
two inches in diameter be supposed to contain all the stars
visible to the naked eye, then it will take a globe 42 feet thick
to contain all the stars visible to our great telescopes.
1 It would be more correct to say that stationary stars equal to Sirius would be
just visible at those distances, and that their light would take so long to reach
us.
2 The same remark applies here.
82 HOW TO KNOW THE STARRY HEAVENS
ETERNAL LIGHT
Suppose that (with the exception of our Sun) every star in
the Universe were to be blotted out of existence to-day, we
should not know of it for several years. We should continue to
receive the light which is already on the way, and the stars
would still appear to twinkle as they have always done. In a
little over four years the nearest star would suddenly go out of
sight. But no one would miss it except the astronomer. After
another four years the mysterious disappearance of Sirius would
attract more general attention. In a century a few more would
be missed, but the majority would remain visible for thousands
of years. Some of the stars seen in the most powerful telescopes
may be so far off that the light we now see left them when
Great Britain was part of the mainland of Europe, and the
Britons were fighting the hippopotamus, the hyena, and the sabre-
toothed tiger.
REASON VERSUS IMAGINATION
I have now given sufficient illustrations of the unthinkable
vastness of the visible Universe. It is no use trying to realise
even ascertained facts of such immensity. As Dr. J. W. Draper
says, " distances and periods such as these are beyond our grasp.
They prove to us how far human reason excels imagination, the
one measuring and comparing things of which the other can
form no conception, but in the attempt is utterly bewildered and
lost."
NUMBERING THE STARS
" Look now toward heaven,
And count the stars.
Tell the number of them
If thou art able." Genesis xv, 5 (A. Zazel).
The next question is, How many stars are there in the visible
and invisible parts of our Universe ?
This, like many other celestial problems, can be only partially
answered. The unaided eye can perceive about 3,000 in each
SOME MORE DIMENSIONS 83
hemisphere. Argelander's great catalogue contains a list of 6"ver
300,000, all visible with a pocket telescope. A good three-inch
achromatic telescope brings about 1,000,000 in sight. But they
are shown by the giant instruments of our great observatories
in such multitudes that they cannot be counted. We have to
be satisfied with more or less approximate estimates of their
numbers.
Yet every improvement in light-grasping power brings mil-
lions of fresh ones into sight, and shows the " backspace " of sky
all glowing with the light of invisible suns too far off to be
separately distinguished.
It has of late years been found possible to attach a photo-
graphic apparatus to a telescope, so as to make the luminous
bodies in the heavens take their own pictures. Whole groups
of stars are photographed on one plate. Complete sets of these
star-photographs (embracing every nook and corner of the celestial
sphere) are taken every year, and carefully compared with one
another, to find out what changes are going on in the heavens.
It will not be long before every star photographically visible to
the most powerful telescope will have its present position accu-
rately defined on these photographic charts.
By a prolonged exposure of the sensitive plate even invisible
stars gradually photograph themselves, so that immense numbers
of stars have been discovered which no eye can see, even with
the aid of the same telescope. " Many ten thousands " of stars
have often registered themselves on a single plate. In one
case over 400,000 were actually counted.
It has been estimated that for every star visible to the naked
eye there are at least 50,000 visible to the telescopic camera.
This would bring the number of visible stars to about 300,000,000.
Yet even the picture-taking power of the photographic tele-
scope has its limits. In photographing the Milky Way its plates
(when long exposed) are sometimes clouded by constellations
too faint, through distance, for the individual stars to record
themselves. However much the telescope and its adjuncts may
be improved in the future, they will always fail to penetrate
84 HOW TO KNOW THE STARRY HEAVENS
more than a certain distance into space. Beyond that limit there
may still be, as George Sterling suggests, the
" fires of unrecorded suns
That light a heaven not our own."
IS THE UNIVERSE LIMITED IN EXTENT?
" The centre of space is everywhere, and its circumference nowhere." Blaise
Pascal.
We know, by abstract reasoning, that space is limitless. The
question arises, Is there a limit to the distribution of luminous
and non-luminous bodies in that limitless space ? In other
words, Is -there a limit to the Universe ?
Professor Newcomb deals with the question as follows. Sup-
pose a globe to encircle and include all the stars visible to the
naked eye. And suppose another of double radius, a third of
treble radius, etc., with similar distribution of stars. As the
light received from a given luminous area or surface is in the
inverse ratio to the square of the distance, each shell will send
us an equal amount of light. If there is no limit, then, unless
some cause produces a loss of light, the whole sky will be as
bright as the Sun. As this is very far from being the case, it is
evident that there is either a limit or a loss of light.
It is not impossible that light itself may have limits to its
continuous flight : that it may be intercepted by dark bodies on
its way to us, or that its waves may lengthen out till all vibra-
tion ceases. Dr. J. J. See says on this subject :
11 In the exploration of the sidereal heavens it is found that the
more power the telescope, the more stars are disclosed ; and hence
the practical indications are that in most directions the sidereal system
extends on indefinitely. But the possible uniform extinction of light
due to the imperfect elasticity of the luminiferous ether, and the un-
doubted absorption of light by dark bodies widely diffused in space,
seem to preclude for ever a definite answer to the question of the
bounds of creation."
FIG. 47. MILKY WAY SURROUNDING MESSIER II.
Photographed with a portrait-leiis, by Barnard, at Yerkes Observatory.
FIG. 48. THE STAR-CLUSTER MESSIER II.
Photographed with the great Yerkes refractor, by Ritchey.
SOME MORE DIMENSIONS 85
So George N. Lowe may be right when he says :
" Beyond the thirty thousand years
Of light, the giant systems swing
Vast, unknown suns and flaming spheres
And great worlds from their girdles fling."
INCOMPREHENSIBLE, YET TRUE
I once put the following question to the late Richard A.
Proctor :
" Let u suppose that a man could reach, in one second of time, the
remotest star visible. Let us also suppose that he could continue on at
the same* speed, in a straight line, to all eternity. Would he ever get
to the end of suns and worlds, or would he always have as many in
front of him as he had behind him ] The latter proposition seems
absurd, yet appears to be a necessary consequence of the theory that
'end there is none, nor is there yet beginning.' But if, on the other
hand, the last star could be reached in every direction, then the Uni-
verse not only has bounds, but is as a mere grain of sand in the infinite
desert of space. Of course I use the word Universe in its largest
sense."
Mr. Proctor's reply was as follows :
" I fear that to this question there is but one answer, ' We don't
know.' The infinite, which necessarily is, is necessarily incompre-
hensible." l
QUANTITY OF MATTER IN UNIVERSE
Of late years an attempt has been made to ascertain the total
amount of matter in the Universe by estimating the gravita-
tional force acting on individual stars. One of these, known
as 1,830 Groombridge, is moving at a speed of 200 miles per
second. Let us suppose that it has " fallen " from a practically
infinite distance, pulled by the combined attraction of every-
thing in our Universe. It has been estimated that more than
30,000,000,000 suns like ours would be necessary to produce
1 See "Knowledge," June 1, 1886, page 254.
86 HOW TO KNOW THE STARRY HEAVENS
the observed speed. If our Sun be taken as an average star,
this would indicate that, for every star visible to the telescope,
there are more than a hundred that are invisible, either from
distance or because they have ceased to be luminous.
If this method be trustworthy, it will give us some idea as to
the dimensions of our Universe. But it does not disprove the
existence of other and similar universes at practically infinite
distances from ours, and from one another. For if it did, then
the observed motion of a comet visiting our Solar System (being
the result of the total attraction of the matter in the system),
could be used as a proof of the non-existence of air^hing out-
side of the Solar System. And this would hardly be doing
justice to the myriads of Stellar Systems which are known to
surround our own.
The Law of Gravitation, which has just been alluded to, will
be dealt with in Chapter XV.
OUTSIDE UNIVERSES
The study of the visible Universe shows that it is composed
of ascending series of similar systems. For example : (1) atoms
appear to be spheroidal " star-clusters " of still smaller particles
in motion ; (2) suns and worlds are rotating spheroids built up
of these atoms ; (3) stellar systems are rotating spheroids built
up of suns and worlds ; (4) the visible Universe appears to be
a rotating spheroid built up of a Milky Way of stellar systems.
It is possible that this largest spheroid, which we call the
Universe, may be only one out of innumerable similar spheroids,
rotating at practically infinite distances from each other, and
forming a still vaster rotating spheroid.
These speculations could be extended ad infinitum at both
ends of the series. It would, however, be a waste of time to
consider them seriously, they only serve to show how little we
really know of the great " Kiddle of the Universe."
CHAPTER VIII
THE PRINCIPLES AND APPLICATIONS OF THE
SPECTROSCOPE
" And Elohim spake unto Noah and to his sons with him, saying ... I will
establish my covenant with you ; neither shall all flesh be cut off any more by the
waters of a flood ; neither shall there any more be a flood to destroy the earth.
And Elohim said : This is the token of the covenant. . . . I do set my bow in the
cloud, and it shall be for a token of a covenant between me and the earth, . . .
and I will look upon it, that I may remember the everlasting covenant." -
Genesis ix, 8-16.
THE BRIDGE OF BIFROST
THE rainbow has always been a source of wonder and ad-
miration to mankind. Before history began, men were
blindly theorising as to the cause and meaning of the wonder-
ful arch of colours which, phantom-like, seemed to span the
earth and reach to heaven. Among the old Norsemen it was
known as the Bridge of Bifrost, and was supposed to connect
the abode of the gods with that of their subjects on earth. No
mortal could set his foot on this bridge, but the gods used it
when they had business to transact or mischief to work in the
lower regions.
In more recent times its nature and cause have been ascer-
tained, and its glorious colours have been reproduced by allow-
ing the Sun to shine through a three-cornered glass prism.
Marvellous to relate, the fragments of rainbow thus produced
have not only helped chemists to solve some of the mysteries
concerning matter on earth, but have also enabled astronomers
to wrest from high heaven many of the secrets relating to the
chemistry, constitution, and movements of the heavenly bodies,
some of which still bear the names of the old deities.
88 HOW TO KNOW THE STARRY HEAVENS
If the old Norse religion had only survived until now, how
easily might the priests of Odin have proved the inspiration of
the old records ! They could now show that the apparently
childish stories (though not literally true) have a hidden sym-
bolical meaning and refer to facts that only Gods could have
then been acquainted with.
But, alas ! the new light has come too late. The old narra-
tives have been replaced by others. The Bridge of Bifrost is
now the only remaining proof that the life of the world was
once practically destroyed by .an all-wise Creator, in a justifiable
exasperation at the moral imperfections with which he had know-
ingly endowed its most perfect inhabitants.
THE KEYS TO THE UNIVERSE
The rainbow and its artificial imitations are caused by the
refraction of light, a property without which mankind would
have been for ever left in the dark as to the outer Universe.
The study of the peculiarities of this refraction has given us the
telescope and the spectroscope two master keys which are
unlocking the mysteries of the Universe to man. The two dis-
coveries have indeed been described by enthusiastic scientists as
the most important events that have taken place on earth since
history began. The telescope, the camera, the spectroscope, and
even the human eye itself, would have been impossible without
the refraction of light upon which they and the rainbow
depend.
The instrument into which the rainbow-like spectrum has
been harnessed is known as the spectroscope. A few words
concerning the principles utilised in this instrument will help
us to grasp some of the facts which have been brought down
from heaven by its means.
MATTER AND ETHER
There appear to be in Nature two forms of substance entirely
distinct from each other in structure and functions. Every
THE SPECTROSCOPE 89
nook and corner of infinite space appears to be packed with one
or the other of these two forms of substance.
I. Matter. That with which we are most familiar is com-
monly known as matter. It is made up of atoms, possesses
weight, and exists as a solid, liquid, or gas, according to sur-
rounding conditions.
II. Ether. The other goes by the name of luminiferous (or
light-bearing) ether. This ether is not made up of atoms, but
appears to consist of homogeneous particles or corpuscles. These
are estimated to be about a thousand times less (in mass) than
the smallest atoms of ordinary matter. On account of their
being the carriers of so-called negative electricity they are
sometimes called negative particles.
This ether is practically without weight, being millions of mil-
lions of times thinner than air. It probably fills to saturation
all space which is not occupied by ordinary matter^ even filling
the little spaces between the atoms of matter. Some of the
phenomena produced by it are explainable only on the theory
that it can pass through suns and worlds as water passes
through a sieve, or as light passes through a massive sheet
of glass. 1
VIBRATIONS OF ETHER
All matter has a life of its own and is in continuous motion.
The various motions of matter produce corresponding vibrations
in the ether, which carries them to inconceivable distances.
Some of these vibrations become sensible to us in the form of
light; others are recognisable as heat, electricity, magnetism,
etc.
REFRACTION OF LIGHT
Light may be regarded as produced by wave-like undulations
of the elusive ether which appears to fill all space. The un-
1 This may at first seem incredible, even with our recent experience of Roentgen
rays. But it must be remembered that it is not a whit more wonderful than the
commonplace yet astounding fact that light can pass, almost without let or hin-
drance, through solid glass or ice.
90 HOW TO KNOW THE STARRY HEAVENS
dulations of light radiate through this ether like the ripples
which spread over water when a pebble is thrown into it. Or
they may more correctly be likened unto the vibrations of air
which start out in all directions from a centre of vibration and
ultimately become sensible to the ear as sound. Like the waves
of sound, the ethereal undulations of light vary in length. That
is to say, the interval between the summit of one wave and that
of the next varies in length in different kinds of light. When
FIG. 49. A PRISM AND ITS SPECTRUM
a ray of white light passes through a glass prism, the greater
density of the medium causes it to be bent or refracted. The
light, instead of coming out opposite to where it entered the
prism, comes out at an angle, the bend being toward the side
where the prism is thickest. The inequality of wave-lengths
causes this refraction to be unequal also, and the white light
splits up into an infinite number of shades, the best known of
which go by the names of violet, indigo, blue, green, yellow,
orange, and red (see Figure 49).
Of these colours the violet rays have the shortest wave-length
and are bent the most from their previous course. The red
waves are the longest, and are bent the least.
This visible spectrum is only a part of a much longer spectrum,
the rest of which is invisible to the eye, though recognisable by
other means. The short waves at the violet end are character-
ised by the intensity of their actinic or chemical properties,
THE SPECTROSCOPE 91
while the long ones at the red end give out more heat. The
violet waves are so short that 61,000 of them reach only an
inch, while the red ones are so long that there are only 33,000
of them to an inch. They all travel at the same speed, 186,000
miles in a second of time. 1
THE SPECTROSCOPE
For convenience the glass prism is placed at the elbow of an
instrument that looks like a bent telescope and is commonly
FIG. 50. A OXE-PKISM SPECTROSCOPE
known as a spectroscope (see Figures 50, 51, and 52). A ray of
white light entering at one end through a narrow slit passes
along the tube until it comes to the prism. There it is bent
and split up into the colours of the rainbow. This row of
colours is known as a spectrum, and is examined directly from
the other end of the " bent telescope."
The spectroscopes now used are more complicated than the
above, with a " battery " of prisms (or with a corrugated mirror
1 It is interesting to note that if the prism, instead of being straight, is bent
around a centre into a lens-form, it 'brings the light to a focus, and forms the
basis of the telescope and microscope. In these instruments special means are
taken to avoid the separation of the various colours, but in the spectroscope spe-
cial means are taken to increase the dispersion.
92 HOW TO KNOW THE STARRY HEAVENS
called a diffraction grating), but they all depend on the same
principle, so need not be here described.
VARIETIES OF SPECTRA
Now it is found that different sources of light do not give
the same spectrum when examined through the spectroscope.
There are, in fact, several distinct classes of spectra, which are
here given.
I. Continuous Spectrum. Light from an incandescent sub-
stance in a solid or liquid state, or from a glowing gas which is
under great pressure, gives a continuous spectrum, all the colours
FIG. 51. SECTION OF A ONE-PRISM SPECTROSCOPE
being fully and evenly represented. In this case it is evident
that light of every wave-length is being given off (see Figure 5 3, a).
II. Emission or Radiation Spectrum. Light from an incan-
descent gas which is uncompressed, and therefore free to vibrate
at its own rate, does not give a continuous spectrum, as in the
first instance. It merely gives a limited number of bright lines,
crossing the long streak where the spectrum should have been.
These bright lines vary in colour according to their position in
the (absent) spectrum. This shows that a glowing gas, when
unconfined, only gives out light of certain definite wave-lengths
(see Figure 53, b, d, e).
III. Absorption Spectrum. When light of the first class
passes through a mass of uncompressed gas, its otherwise con-
tinuous spectrum becomes to a certain extent discontinuous.
It is crossed by certain dark lines, making the spectrum look as
though there were a ladder in front of it, with numerous black
rungs at irregular distances from one another. This shows that
light of certain wave-lengths is absent, being absorbed by the
THE SPECTROSCOPE 93
uncompressed gas through which the light passes (see Figure
53, i, etc.).
IV. When the source of light is partly solid or compressed
matter, and partly uncompressed gas, the result is a spectrum
crossed by lot h bright and dark lines or bands (see Figure 53, h).
FIG. 52. A COMPOUND SPECTROSCOPE
SPECTRUM ANALYSIS
Chemists have discovered that there are only about eighty
different kinds of matter on the accessible parts of our globe,
and that only about a quarter of these are abundant or im-
portant. All the tens of thousands of different substances on
earth (whether solid, liquid, or gaseous) consist of these elements,
either separate or in partnership with one another.
Now the great importance of the spectroscope depends on
the fact that every one of the elements, when in the condition
94 HOW TO KNOW THE STARRY HEAVENS
of glowing gas, produces its own special lines in the spectro-
scope. By examining the spectrum of an unknown substance,
the elements of which it is composed can be ascertained. This
way of examining substances is therefore known as spectrum
analysis.
It has also been found that when light passes through a cer-
tain uncompressed gas, that gas absorbs the same rays of light
which it naturally emits when it is itself an uncompressed
source of light (see Figure 53, b, c).
Bearing these facts in mind, let us turn back to reconsider
the four classes of spectra given above.
When the spectrum is of the first class (continuous), we do
not get much information with regard to the source of light.
We know that the light does not proceed from an uncompressed
gas, but we cannot tell whether it is given off by a solid, a
liquid, or by a compressed gas.
When it is of the second class (emission), consisting entirely
of a limited number of bright lines, we know that the light pro-
ceeds from a glowing gas that is not under great pressure. And
we can tell what particular elements that gas consists of or con-
tarns. Certain lines prove that it contains hydrogen; other
lines tell of the presence of sodium. Another set is caused by
iron vapour; and so on, with all the elements (see Figure 53,
b,d,e,f).
When the spectrum is of the third class (absorption), it is
nearly continuous, but is crossed by dark lines. In this case
we know that the luminous body, whatever it is, is surrounded
by uncompressed gas which has absorbed certain light-waves
and so prevented them from reaching us, and, as in the second
class, we can tell what particular elements that gas consists of
or contains ; for the element which produced a certain set of
bright lines when it was a source of light produces the same set
of dark lines when it surrounds the source of light or comes
between the source of light and its spectrum. Hydrogen,
sodium, iron, etc., are in the one case recognised by their pecu-
liar bright lines, and in the other case by identical sets of
THE SPECTROSCOPE 95
dark lines. The difference is one of condition, not of substance
(see Figure 53, 6, c).
A spectrum of the fourth class, crossed by both bright and
dark lines or bands, denotes that the source of light is either a
mixture of solid and gas, or of compressed and uncompressed
gases. The different sets of lines denote the presence and con-
dition of their respective elements, as in the other classes.
In spite of the one element of uncertainty mentioned, the
above results are remarkable achievements, even when applied
to substances actually present in the chemist's laboratory.
They have led to the discovery of hitherto unknown elements
and to a great advance in chemistry generally. But still more
remarkable is the fact that this spectrum analysis can be applied
to a distant source of light. Large numbers of the terrestrial
elements have been recognised in the sierra or atmosphere of
our Sun, and even the stars are not too far off to be cross-
examined by the spectroscope as to their chemical composition
and physical condition.
The spectrum of a star being very faint, it is observed by a
spectroscope attached to a telescope, the combination being
known as a tele-spectroscope (see Figure 54). Sometimes the
spectrum is photographed for future .examination and com-
parison. The instrument which accomplishes this is termed a
spectrograph (see Figure 55).
SPECTRA OF STARS
Our Sun and the brighter stars, when examined with the spec-
troscope, give spectra of the third class (absorption). That is to
say, their spectra are fairly continuous, but are crossed by dark
lines. This shows that such stars are all related to one another,
so that the study of any one of them will throw light on all the
rest. They are all suns, somewhat similar to, but not identical
with, our Sun (see Figure 53, i,j, Jc, I, m).
The fainter stars have not yet been satisfactorily examined
with the tele-spectroscope, on account of the small quantity of
light we receive from them. Still, a certain amount of infor-
96 HOW TO KNOW THE STARRY HEAVENS
mation has been obtained concerning their composition and
condition. -
SPECTRA OF NEBULAE
When the heavens are examined with the help of a telescope
of some considerable power, enormous numbers of stars are
revealed. But, besides these stars, the telescope also brings
into sight large numbers of tiny patches of hazy light. These
look as though they might be clusters of stars which are too
far off to be separately distinguished. From their cloud-like
appearance these streaks and patches are termed nebulce. 1
With two or three exceptions these nebulae are not visible to
the naked eye, and the vast majority of them require very
powerful instruments to bring them into view.
Modern telescopes have in many cases proved that they are
really composed of stars, and every increase in telescopic power
has resolved fresh nebulse into star-clusters. At one time it
was thought that all would eventually be proved to be nothing
more or less than clusters of faint stars. It has been ascer-
tained, however, that there are two main classes of so-called
nebulse, and that only those of one class are composed of stars.
PSEUDO-NEBULAE (Star- Clusters). All of those nebulse which
have been shown by the telescope to be really star-clusters give
absorption spectra similar to those of the visible stars (Class III),
and some nebulae which have not yet been resolved into stars by
the telescope have been found to give similar spectra. As a
rule the spectrum of a star-cluster is so faint that it consists of
a mere streak of light in which the colours and lines are imper-
ceptible.
TRUE OR GASEOUS NEBULAE. Other nebulas, however, show
by their bright-line spectra (Class II) that they are not com-
posed of suns, but are immense masses of glowing gas, not under
pressure. Those which are comparatively bright give a number
of bright lines, five of which are much more prominent than the
1 The Latin word nebula means a cloud, fog, mist, or smoke. It may be regarded
as a diminutive of nubes,a. cloud.
FIG. 54. TELE-SPECTROSCOPE
Attached to a telescope for the purpose of viewing celestial spectra. Lowe Observatory.
FIG. 55. THE MILLS SPECTROGKAPH AT LICK OBSERVATORY
For photographing spectra of celestial objects.
THE SPECTROSCOPE 97
rest. In the fainter nebulae only one of the lines is visible,
owing to the small quantity of light which reaches us ; but it is
readily distinguished from the practically continuous spectrum
given by star-clusters, etc.
CLASSES OF STARS, ETC.
Stars and other self-luminous heavenly bodies have been
divided into a number of classes, according to their colours and
spectra ; but no hard-and-fast line can be drawn between them,
as there are many which give intermediate spectra. The fol-
lowing are perhaps the best defined classes, starting with the
youngest.
A. BLUE-GREEN NEBULA (G-aseous Nebulce). Nearly a hun-
dred of the nebulae have a bluish-green tint which distinguishes
them from all others. They give an emission spectrum, con-
sisting entirely of a few bright lines (Class II) on a dark back-
ground. This indicates that they are entirely composed of
uncondensed gases, so extremely diffuse as to be transparent in
spite of their thickness, which is sometimes many millions of
miles. The lines are those belonging to hydrogen, helium, and
" nebulum " (see Figure 53, g). The lines are thin, denoting a
comparatively low temperature and the absence of pressure.
One of these lines, in the blue-green part of the spectrum, is so
bright that it gives the blue-green tinge peculiar to nebulas of
this class when seen through the telescope. It is due to an
unknown substance which has been named " nebulum."
About half of these gaseous objects are termed planetary
nebulce, from the symmetrical planet-like disc which they ex-
hibit when seen through a powerful telescope (see Figure 99). 1
The rest are generally irregular and shapeless, like the Great
Nebula in Orion (see Figure 68), and the Trifid Nebula in Sagit-
tarius (see Figure 67). The so-called King Nebula in Lyra is
also gaseous. Recent photographs taken at the Ann Arbor
Observatory by Professor Schaeberli show that its resemblance
1 Some of the planetary nebula have a star-like nucleus in the centre,
7
98 HOW TO KNOW THE STARRY HEAVENS
to a ring is only apparent, and that it is really a spiral nebula
(see Figure 66).
B. PEAKLY- WHITE NEBULAE. Some thousands of nebulae
have a pearly-white appearance when seen through the tele-
scope. They give a continuous spectrum, which denotes that
they are either composed of matter in a solid state, or of gases
under high pressure or great heat. Very little is at present
known as to the actual condition of the matter composing
these nebula3. But in many cases it appears to be collecting
in " centres of condensation," as though stars were in process
of formation out of nebulous matter.
The Great Nebula in Andromeda (see Figure 64) belongs to
this class, as do the spiral nebulce generally (see Figure 63).
The late Dr. Keeler estimated that there are at least 120,000
nebulae within range of the telescopic camera, and that more
than half of these show signs of a spiral structure.
C. NEBULOUS STARS (Orion Stars). These consist of a faint
nebulous haze with a star in the centre. They give broader
hydrogen and helium lines than Class A, showing that the gases
are hotter and more condensed. These stars are still in process
of formation, and have not yet drawn in all of the nebulous
matter around them. They are therefore buried in the depths of
a luminous haze consisting chiefly of hydrogen and helium.
Examples, the stars in the Pleiades and those connected with
the Great Nebula in Orion.
D. BLUISH-WHITE STARS (Sirian Stars). About 75 per
cent of the brighter stars appear to belong to this class. Their
spectra show all seven colours (Class III), but the violet end is
the most brilliant. There are four broad dark lines belonging
to hydrogen, greatly condensed and very hot. The metal lines
are few and faint. One of the magnesium lines indicates a
temperature about equal to that of the electric spark, say
about 20,000 F. The probability is that these stars are still
surrounded by a very deep, dense, and hot atmosphere (chromo-
sphere) of hydrogen, and that the high temperature prevents
the formation in it of a bright cloud-photosphere of calcium, etc.
w 8
THE SPECTROSCOPE 99
Examples, Sirius, Vega, Altair, Rigel, and Arided (see Figure
53,y,*>
E. YELLOWISH STARS (Solar Stars). This class includes
about 23 per cent of the brighter stars. Their spectra show all
seven colours (Class III), the middle being the most brilliant.
The hydrogen lines are faint, denoting a shallower atmosphere
or chromosphere. There are large numbers of very strong dark
absorption lines, due to the presence of different metals (in the
gaseous state) in the stellar atmospheres. Many of these metal-
lic elements have been recognised by their special lines. One
of the magnesium lines indicates a temperature not very far
from that of the electric arc (6,300 F.), or at least it indicates
a temperature lower than that of the electric spark. Probably
12,000 F. is not very far from the mark. The comparatively
low temperature of the chromosphere due to its shallowness
causes the formation of a layer of bright clouds known as
the photosphere. This is composed of incandescent solid (or
liquid) particles of calcium, etc.
If all the light from this brilliant photosphere reached us,
the Sun and solar stars would all be of a pure white, and their
spectra would be continuous (Class I), containing rays of all
wave-lengths. But as they are surrounded by a chromosphere
(or atmosphere) of metallic gases at a rather lower temperature,
some of the light is absorbed. The absorption is greatest among
the short waves, so that these stars all have a yellowish tinge.
Their spectra are therefore of Class III, with many dark absorp-
tion lines due to the metallic gases in their chromospheres.
Examples, Capella, our Sun, Procyon, Pollux, and Arcturus
(see Figure 53, 1 ; also Figure 56).
F. ORANGE-RED STARS. This class includes about one per
cent of the brighter stars. More than 60 of them are irregular
variables of the Mira Ceti class. The spectra show all the seven
colours (Class III), with the red end most brilliant. There are
no hydrogen lines except when the stars are at their maximum
of brilliancy. The metal lines are complex, and there are dark
absorption-bands, with a sharp, well-defined edge toward the
100 HOW TO KNOW THE STARRY HEAVENS
violet. These indicate a dense and complex atmosphere of rela-
tively low temperature, with chemical compounds. Examples,
Aldebaran, Betelgeuse, Antares, and Mira Ceti (see Figure
53, i).
G. BLOOD-RED STARS. The spectra are similar to those of
Class F, but are more or less cut up by dark absorption-bands.
These have a sharp, well-defined edge toward the red end of the
spectrum, and are due to hydrocarbon vapours in the stellar
atmospheres. In some stars these bands are so broad and dark
that but little of the spectrum can be seen. Their light is in
fact dying out. Examples, Mu Ceph, and 152 Schjellerup (see
Figure 53, m ; also Figure 57).
H. DARK SUNS. These give out little or no light and heat,
and therefore have no visible spectra. They are dead or dying
suns. We know of their existence only when they have visible
companions moving around the same centre of gravity. Ex-
ample, one of the companions of the Pole Star.
RADIAL MOTIONS
Of late years the tele-spectroscope has given aid to astronomy
in another and unexpected direction. Astronomers have long
been able to watch and measure the movements (both real and
apparent) of the heavenly bodies when those movements were
more or less at right angles to the line of sight. But until
recently they were unable to detect motions toward or away
from us, except indirectly, by the increase or decrease of bril-
liancy and size.
A few years ago, however, it was discovered that, when a
source of light is approaching, the lines which cross its spectrum
are displaced toward the violet end, and that when it is receding
they are displaced toward the red end of the spectrum.
This is due to the same cause that makes a locomotive whistle
appear to fall in pitch the moment it passes the listener. While
the engine was approaching the listener, the waves of sound
reached his ear at shorter intervals than they would otherwise
fa -U
THE SPECTROSCOPE 101
have done, and after it has passed him the reverse is the case.
Hence the apparent change of pitch.
In the case of light (spectroscopically observed), j the effect is
a slight change of position instead of pitch:, t <yh$;wi\v$s aieiu
fact crowded together and made shorter from, crest , to, jerest. .
This could not be measured or even recognised in -a cont^u-yds
spectrum, but in a banded one it is done with comparative ease
by so arranging as to have a normal spectrum on each side of it
for comparison (see Figure 58). The result is that we can not
only tell that a certain object is approaching or receding from
us, but can also tell how many miles it is moving in those
directions per second.
This method of detecting and measuring radial motions (real
or apparent) can be applied not only to those heavenly bodies
whose distances are known, but also to those which are utterly
beyond the reach of our space-measuring instruments. The
only limit is that caused by deficiency of light.
It is possible that this principle may in time be found avail-
able for measuring star-distances which are too great for our
present methods. It is proposed to measure the orbits of double
stars spectroscopically, and then use the major axes as base
lines.
At present, stellar distances can be roughly estimated up to
60 light-years, which is 15 times the distance of Alpha Cen-
tauri. Dr. See thinks that some day star-distances of 1,000
light-years may be determined by this plan.
CHAPTER IX
A STAR-SPANGLED BANNER
" The winter sunset fronts the North,
The light deserts the quiet sky,
From their far gates how silently
The stars of evening tremble forth !
" Time, to thy sight what peace they share
On Night's inviolable breast !
Remote in solitudes of rest,
Afar from human change or care.
"Eternity, unto thine eyes
In war's unrest their legions surge,
Foam of the cosmic tides that urge
The battle of contending skies.""
George Sterling, " The Testimony of the Suns."
STAR MAGNITUDES
" One star differeth from another star in glory." I Cor. xv, 41.
THE stars are at such vast distances from us that in spite
of the enormous sizes of some of them they all appear as
mere points of light. This is true even with the most power-
ful telescope in existence. Only one star in the heavens is
near enough to show a measurable disc, and that is the one
which rules our own system under the names of Helios,
Shemish, Baldur, Father Sol, the Sun of Kighteousness, and a
thousand other suggestive names.
But this does not mean that the stars all look alike, either
with the naked eye or with the telescope. There are stars of
almost all colours, and even those which appear to be of the
same colour differ enormously in brilliancy. Sirius scintillates
in the sky like a sparkling jewel, and glares down the telescope
A STAR-SPANGLED BANNER 103
tube like a little sun, so that he is better examined with a dark
glass. A few other stars are not far behind in brilliancy.
Large numbers are fairly bright, while swarms of them are com-
paratively inconspicuous. Still larger numbers are just visible
to the naked eye, and the telescope reveals them in multitudes
that no man can number. Yet no two of them send us exactly
the same amount or quality of light.
It has been found convenient to classify the stars according
to their brilliancy. At first the classification was rude, but of
late years they have been sorted out with considerable accuracy.
They are divided into a number of magnitudes, a star of one
magnitude being 2 J times as bright as one of the magnitude
below it. l
Thus a star of the first magnitude sends us 100 times as
much light as one of the sixth magnitude, which is the faintest
star visible without a telescope. And that is 100 times as bright
as one of the eleventh magnitude, which in its turn is 100 times
as bright as one of the sixteenth. This rule applies to all magni-
tudes. Taking Aldebaran as a standard star of the first mag-
nitude, the North Pole Star belongs to the second, and the
brightest star of the Pleiades to the third. The rest of the
bright stars in the same group belong to the fourth. The
faintest stars usually seen belong to the fifth, and those just
visible by direct vision on very clear nights are of the sixth
magnitude. The seventh magnitude stars can just be glimpsed
by oblique vision, by unusually keen eyes, on exceptionally
clear occasions.
There are a few stars brighter than Aldebaran, and these are
sorted out in the same way, with the numbers reversed and the
minus sign ( ) placed in front of them, instead of the plus sign
(+), which is sometimes used to denote the regular magnitudes.
Thus one magnitude brighter than the first is denoted as (0),
the next (1), and so on. On this plan Sirius is denoted by
the sign (1.4), his brilliancy being 9.1 times greater than that
of Aldebaran. And our Sun is a star of the magnitude 26.4,
!More exactly, 2.512.
104 HOW TO KNOW THE STARRY HEAVENS
his apparent brilliancy being about 90,000,000,000 times greater
than that of Aldebaran.
It must be understood that the magnitude of a star does not
denote its real size, or its weight, or the actual amount of light
given off by it, or its distance from us. It merely denotes the
amount of light we receive from it, and this depends on a com-
bination of these factors, which are unknown to us in the vast
majority of cases. For example, Canopus, which is the second
brightest star in the heavens, is at an immeasurable distance
from us, and must therefore be many thousands of times larger
and brighter than our Sun. And some of the fainter stars
visible to the telescope may be even larger than Canopus. On
the other hand, some fairly brilliant stars are smaller even than
our Sun, their distances from us being comparatively small, as
stellar distances go.
For this reason the actual and apparent motions of the stars
form a better guide to their distance, size, and actual brilliancy
than do their magnitudes. We have an example of this in the
star known as 61 Cygni, which is nearer to us than Sirius,
although it is nearly seven magnitudes smaller and sends us
nearly 600 times less light.
The number of visible stars has been already dealt with. It
may, however, be interesting to know that there are about 50
stars of the second magnitude (from 1.6 to 2.4), and about one
third that number of larger ones. Also that, from this down,
each magnitude has about three times as many as the one
above it. To the fourteenth magnitude (14.5) this would give
200,000,000, stars. With the fainter stars, however, the in-
crease in numbers appears to be less rapid. The faintest stars
visible to the eye in the great Lick telescope are of about the
seventeenth magnitude.
ACTUAL BRILLIANCY OF VISIBLE STARS
The actual magnitudes of the stars may be considered from
three distinct standpoints, (1) Mass or Weight; (2) Size;
(3) Brilliancy. We will here consider the brilliancy alone,
A STAR-SPANGLED BANNER 105
as comparatively little is at present known of the other two
factors.
It must be remembered that stars which now give out little
or no radiant energy are not necessarily small. Some of the
largest suns in the Universe are feeble from extreme old age,
while others are dead and cold, waiting patiently for the resur-
rection that comes through collision.
If the stars were all at the same distance from us, their actual
brilliancy would be proportionate to their apparent magnitudes,
and could therefore be easily found. On the other hand, if
they were alike in actual brilliancy, we could estimate their
distances from us by that alone.
As it is, however, with varying distances and sizes, the prob-
lem is a difficult one, and will probably never be solved except
in the case of the nearer stars. I can give here only a few
illustrations of what has been ascertained concerning the radiant
energy of the stars.
Let us first consider what we may reasonably expect to find,
and then compare our expectations with the results actually
attained.
Take a certain distance, A L, and divide it into 11 regularly
increasing intervals. Call these shorter distances B, C, D, etc.
Let us suppose that we are at A, and that there are 10 stars
at the distance B. The actual brilliancy of these stars we may
suppose to vary regularly, so that (from A) the largest appears
equal to Sirius, and the smallest is just visible. If there be a
similar set at each of the other distances, only 9 of those at C
will be visible. Of those at D only 8 will be seen. And so OD.
Those which become invisible will of course be the smallest,
but, as the others will appear smaller on account of the greater
distance, the effect will be as though the largest were dropped.
Beyond the distance K all will be invisible. Out of the 110
stars only 55 (one half) will be visible to us. We may expect,
therefore, to find all sizes of stars among those nearest to us,
while at the limit of visibility only the very largest will be
visible, and they will appear very faint. For every star visible
106 HOW TO KNOW THE STARRY HEAVENS
there will be at least one invisible. This reasoning may be
applied to telescopic stars as well as to visible ones.
First Step. It is found, however, that there are no very
large stars among those which are near to our System. The
largest, both actually and apparently, is Sirius, which equals
about 30 suns like ours. Procyon, Altair, and Alpha Centauri
are also brighter than our Sun. The fifth-magnitude star known
as 61 Cygni is small, and some of the binaries and multiple
systems contain stars which give out hundreds and thousands
of times less light than our Sun.
Second Step. If we examine those which are very much
farther away, but are still at a measurable distance from us, we
find stars which have much more actual brilliancy than any of
the nearest stars. And some of them, in spite of their great
distances, are equal in apparent brilliancy to any of the nearest
stars, with the single exception of Sirius. Those known as
Arcturus, Eegulus, Antares, and Gamma Cassiopeise, are each of
them about equal in brilliancy to 1,000 suns like ours, rolled
into one huge globe.
Third Step. Among those which are at absolutely immeas-
urable distances from us we should not expect to find any stars
equal in apparent magnitude to those which are so much closer
to us. But here we meet with another surprise. For some of
them are among the brightest stars in the heavens. They in-
clude, indeed, the second brightest star in the sky. Rigel, Can-
opus, and Arided are each of them many thousands of times
larger and more brilliant than our Sun. In fact they are so
large and brilliant that they exceed our Sun as much as it
exceeds the planets which yield to its authority. They are so
enormous that the mind cannot grasp their immensity. They
may be the centres of systems of a higher order than ours, with
mighty suns for planets, huge planets for satellites, and perhaps
secondary satellites revolving around the primary ones.
Yet, for all we know to the contrary, some of the faint stars
that fill the back-space of sky may exceed them as much as
they exceed our Sun.
A STAR-SPANGLED BANNER 107
We have now taken three huge steps into the visible Uni-
verse, and at each step have found larger suns than we had
come across before. And the fact that some of those that are
at an immeasurably great distance from us are quite brilliant
when seen from the Earth shows that several more such steps
will have to be taken before we get beyond the great mass of
fairly visible stars. This is true of those seen without the aid
of the telescope, and it is much more true of telescopic stars.
DARK SUNS AND PLANETS
It has been already mentioned that some stars are not now
luminous, their heat having radiated into space and left them
dark and cold. There is some reason to believe that the Uni-
verse is crowded with these dead and dying suns, and that they
are in fact vastly more numerous than the living ones. Besides
these, there are the planets which probably swarm around each
and every star, living and dead. Our own star has countless
millions of such bodies revolving around it. Probably about a
thousand of these are large enough and near enough to be de-
tected by our telescopes, the smallest one visible (a satellite of
Mars) being about seven miles thick. All the rest are too
small or too distant to be seen by us. The only evidence we
have of their existence is that they occasionally run up against
our atmosphere, and are turned to flaming gas by the friction.
Sometimes fragments of them reach the Earth's surface in a
solid state, unaltered except at the original surface, which is
vitrified by the heat.
VARIABLE STARS
While sorting out the stars according to their magnitudes,
astronomers have discovered that large numbers of them vary
in brightness at different times. They are therefore called
" variables," to distinguish them from those which give out a
steady unfluctuating light.
108 HOW TO KNOW THE STARRY HEAVENS
REGULAR (SHORT-PERIOD) VARIABLES
Algol Variables. Some of these variables are periodic and
regular in their changes. For example, Algol, which is usually
of the 2.3 magnitude, fades every three days to the 3.5 magni-
tude, and recovers its normal brightness in a few hours. The
spectroscope shows that between these minima it is alternately
approaching and receding from us.
It is evident that in this case there are two stars revolving
around their common centre of gravity, but that one of them is
smaller and gives out little or no light. When it passes be-
tween us and Algol it partly eclipses the latter.
The period of revolution (three days), and the speed at which
Algol moves to and from us, show that they are about 3,000,000
miles apart. The invisible companion appears to be about the
size of our Sun, and Algol larger. But their masses, taken to-
gether, are probably less than half that of our Sun alone. 1
Speetroscopic Double Stars. Beta Lyrae is also a periodic
variable, with partial eclipses every 6^ days. But in this case
only the alternate minima are equal. The spectroscope shows
the usual spectral lines to be doubled. There appear to be two
unequal self-luminous stars revolving around each other, about
30,000,000 miles apart.
It is obvious that these two classes of variables, which are
both regular in their fluctuations, are only apparently variable,
through change of position. Their actual brilliancy remains
the same. Most of them are white stars.
Stars below a certain magnitude cannot be satisfactorily ex-
amined spectroscopically, on account of the faintness of their
spectra. Among the stars which have been so examined, about
one in seven shows some inequality of radial motion, due to
large invisible companions.
IRREGULAR (LONG-PERIOD) VARIABLES
Mir a Ceti Variables. Other variable stars (which are
generally red) differ from the above in being irregular, both as
1 One variable of this type has a period of only 4 hours.
FIG. 59. COLOURED DOUBLE STARS
A STAR-SPANGLED BANNER 109
to time and brilliancy of maxima and of minima. Mira Ceti,
for example, has a maximum varying from the second to the
fifth magnitude, and a minimum varying from the eighth to
the ninth magnitude. Its period also varies irregularly, -being
usually about eleven months.
The cause of such irregular fluctuations must be violent
physical and chemical reactions such as take place on all large
cooling bodies at certain critical temperatures. Even our Earth
has passed through such crises in the past, and our Sun has
slight spasms every eleven years from the same cause. Some
day, when chemical compounds are formed on the cooling sur-
face of the Sun, these fluctuations will be vastly greater than
they are now.
NEW STARS
" Vague on the night the mist we mark
That tells where met the random suns." G. Sterling.
Allied to these irregular long-period variables are the new
stars which occasionally flash out in a hitherto vacant part of
the sky, attain a maximum brilliancy in a few days, and then
slowly die out again. These either disappear altogether or re-
main as telescopic stars. The New Star in Perseus is a familiar
example of this class. Inside of five days it increased from
telescopic invisibility to be the brightest star in the Northern
Hemisphere (magnitude 0). It then faded gradually away, and
in a few months became invisible to the naked eye.
While this star was increasing in brilliancy, the spectroscope
showed an almost continuous spectrum, like that of other stars
(Class III). But bright and dark bands gradually appeared
in it (Class IV), and it ended by resembling the spectra of
the true nebulae (Class II).
This star's sudden appearance was not due to its coming
toward us out of the depths of space. It was probably caused
by a sudden and stupendous discharge of light and heat from
a previously existing star or stars. Such an outburst may be
produced in several ways.
ilO HOW TO KNOW THE STARRY HEAVENS
For example : (1) two stars or planets may come into more
or less direct collision, and spread out rapidly into a huge
nebula of flaming gas. This will cool down in a short time to
the temperature of space. Or (2) the colliding stars may strike
a glancing blow and cut slices out of each other. In this case
the slices alone will turn to gas, while the wounded stars will
enter into partnership, revolving around their common centre
of gravity. Or (3), the stars may not strike, but pass so close
to one another that their solid crusts are rent asunder by tidal
action, exposing the molten interior of one or both of them.
Or (4), a dark star may, in the course of its wanderings, dash
through an immense swarm of "pocket planets," commonly
known as meteoric bodies. Such a collision will turn the
meteorites into gas, and, if they are numerous enough, their
dissipation will cause a temporary brilliancy like that observed.
Or (5), a single cooling body may reach one of its " critical "
periods, and flare up from sudden physical or chemical reactions,
like those attributed to Mira Ceti, only more severe.
Collisions and minor interferences between all kinds of
heavenly bodies must, in the very nature of things, take place
now and then, seeing what multitudes of suns and worlds are
hurtling through space, in all directions, without any one on
board to guide them. And at the same time collisions appear
to be necessary to prevent the Universe from dying of old age.
The dead or dying hulks collide, turn to gaseous nebulae, and
start afresh to form new systems of suns and worlds.
DOUBLE AND MULTIPLE STARS
" Those double stars
Whereof the one more bright
Is circled by the other." Tennyson.
In dealing with periodically variable stars it was shown that
they are really double-star systems with orbits turned edgeways
to us. There are immense numbers of similar systems which
do not happen to be so situated, and are therefore not recognis-
able as " doubles " by the spectroscope. Some of them, however,
A STAR-SPANGLED BANNER 111
are so near to us, or have such large orbits, that the telescope
itself enables us to detect their "duplicity" and follow their
motions. There are over 10,000 double stars now known. In
about fifty cases the time of mutual revolution has been deter-
mined with some certainty. The periods vary from 5.7 years 1
(the shortest telescopically visible) to 1,500 years. Many bi-
naries take thousands of years to complete a revolution, and
their motions have not been followed long enough to fix their
orbits and periods.
Those dual systems of suns which started as partners not
by direct collision, but by tidal division, are twins, their gase-
ous contents having, at first, the same -heat and condition. It
takes longer for a large mass to condense into a sun, and then
cool off and die of old age, than it does for a smaller one. There-
fore the larger of the two bodies is relatively younger than its
companion, and the centre of brilliancy of its spectrum should
be nearer to the violet end. Dual systems which started in
other ways would not necessarily have this spectral peculiarity.
For some unexplained reason there is much more variety of
colour in double stars than in single ones. They are sometimes
of a green, blue, or violet colour (see Figure 59).
In some cases there are more than two suns in the same sys-
tem. The North Pole Star, for example, has two companions
large enough to be classed as suns, though one of them has
ceased to give out any appreciable light and heat.
There appears to be every gradation of solar systems visible
to the telescope. They vary from simple ones like ours, to
highly complex star-clusters, like the one in the constellation
of Hercules. This has over 6,000 visible suns, and appears to
be surrounded by long spirally radiating wisps of nebulous mat-
ter in which other stars are entangled.
SOLAR DRIFT.
It has long been known that some of the nearer stars are
not absolutely fixed, but are slowly changing their positions in
l Delta Equulei.
112 HOW TO KNOW THE STARRY HEAVENS
the heavens. And the spectroscope has told us that, while some
stars are coming nearer to us, others are retreating. From the
nature of the evidence we may safely assume that all stars are
in motion, and that our Sun partakes in this stellar drift,
carrying its planets along with it.
If our sun be assumed to be motionless, then the observed
motion of a star must be real, due to its own drift through space.
But if our System is also adrift, the observed motion of a star
may be only apparent, due to our own change of place. Or it
may be partly real and partly apparent.
It is obvious that, if our Sun is drifting in one direction
(carrying us along with it), the stars toward which it is drifting
will appear to open out or separate, while those from which it is
retreating will appear to close up. At the same time those
which we are passing will appear to drift backward.
Now the telescope shows that all three of these peculiarities
are actually taking place. The stars around Vega, in the con-
stellation of the Lyre, are gradually separating from one an-
other, those on the opposite side of the heavens are as gradually
closing up, and those at right angles to this line of march are
drifting backward.
The conclusion is obvious. The motions of the stars are, at
least in part, only apparent. Our whole System is drifting in
the direction of Vega.
Lest we should have made a mistake, let us inquire of the
tele-spectroscope, and find out which stars are approaching us
and which are receding.
According to the spectroscope and spectrograph, the major-
ity of the stars about Lyra are approaching us at the aver-
age speed of about 12J miles a second. And the majority
of stars opposite that constellation are receding from us at
about the same rate. In the circle of the heavens between
these two points there is no decided motion either to or
from us.
We thus see that two absolutely independent sets of evidence
both point to the same conclusion. Our Sun is drifting toward
FIG. 60. STAR- CLUSTER IN HERCULES
Lick photograph.
A STAR-SPANGLED BANNER 113
Vega at the rate of 12| miles a second, and all the planets share
in the " solar drift."
On account of this solar drift, the orbit of the Earth, in-
stead of being an ellipse, is really of a corkscrew shape, the
axis of the " corkscrew " being in the direction of the constel-
lation Lyra. 1
STELLAR DRIFT
After allowing for the apparent motions of the stars, due to
our own drift, there remain certain real motions of the stars,
due to their own drift.
For instance, the telescope shows that the star known as
1,830 Groombridge is moving steadily along at the rate of over
200 miles a second. Some other stars have motions as real,
though not as rapid. The spectroscope shows that some stars
are actually approaching us, while others are as actually reced-
ing from us.
In some cases a number of stars are drifting along together,
showing that they form a family group. The Pleiades form
a familiar example of this social drift through space.
1 The Cluster of Hercules is not very far away from the part of the sky which
we are approaching. It is possible that our System may form a distant part of
one of its encircling wisps of star-strewn nebulous matter. In this case we may
eventually be drawn into the cluster.
CHAPTER X
CONSTRUCTION OF THE UNIVERSE
"Secondly, . . . what is the arrangement of the stars in space? Especially,
what is the relation of the Galaxy to the other stars ? In what senses, if any,
can the stars be said to form a permanent system ? Do the stars which form the
Milky Way belong to a different system from the other stars, or are the latter a
part of one universal system ? " Prof. Simon Newcomb.
DISTRIBUTION OF STARS
IN the stellar population of the visible Universe there are
very great differences of distribution. Although it would
be difficult to point a powerful telescope to any part of the sky
and find the field of view absolutely hare of stars or nebulae,
yet in some directions they are very much more scarce than in
others. In fact the visible inhabitants of space are as unevenly
distributed as is the human population of Usona. There are
belts of sky that are swarming with cities, towns, and villages
of social stars, and have the intervening spaces well peopled
with more independent families. And there are large tracts
of sky that are comparatively thinly inhabited with visible suns.
Some of the star-clusters are almost as crowded as are our cities.
In some of the thickly settled tracts nearly all the stars are well
developed, while in others large numbers of the inhabitants are
in a nebulous embryonic stage.
ALL SORTS AND CONDITIONS OF SUNS
In that part of the Universe which is at present visible from
our Earth, there are many different structures and styles of
architecture. And all stages of construction and development
are represented. There are systems that appear to be still in
the throes of birth; systems in young and vigorous growth;
CONSTRUCTION OF THE UNIVERSE 115
systems in the strength and pride of maturity ; systems that are
tottering toward the grave ; and systems that are cold in death
and waiting for the resurrection that will surely come.
THE CONSTELLATIONS
The stars that are visible to the naked eye have long been
divided up by man, for his own convenience, instruction, and
amusement, into groups or constellations. About 48 of these
are extremely ancient, and the rest are quite modern.
The ancient constellations appear to have had a priestly origin
and an important religious significance. The stars were divided
into groups, each of which was supposed to form a picture of
some person, animal, or inanimate object. The 48 constella-
tions contained 54 figures, which formed a huge sky-picture
whose mystic meaning has long been lost sight of by the
multitude.
These fanciful figures appear to have been invented by a
people who lived south or southeast of the Caspian Sea, nearly
5,000 years ago. As the stars near the South Pole were invisi-
ble from their part of the world, they naturally left that section
of the sky unfigured. The size of the circle which was left
blank shows us that the constellation-makers lived about 39
north of % the Equator. And the animals, etc., which they pic-
tured in the sky, tell us their longitude on the earth ; for they
naturally depicted the animals with which they were acquainted,
and none others. Even the animal monstrosities were combi-
nations of familiar animals.
Owing to what is known as the Precession of the Equinoxes
(described in Chapter XII), this circular blank space does not
now centre at the South Pole, and the amount of its drift tells
us that the constellations were completed about 2800 B. c.
The first groups of stars to be pictured out were evidently the
twelve Signs of the Zodiac, likewise known as the "Mansions
of the Sun." The picture-makers were, astronomers of no mean
ability. They had already determined the length of the year
116 HOW TO KNOW THE STARRY HEAVENS
with some degree of accuracy. They had recognised the fact
that the stars are in the sky during the daytime, though they
cannot then he seen under ordinary circumstances. They had
even traced out the annual path of the Sun among the stars.
This was a remarkable achievement which few of us would have
the patience and ingenuity to accomplish unaided. To do it they
must have rigged up some sort of equatorial mounting, with
a number of pointers directed to the most prominent stars.
To enable them to ascertain the Sun's position in this path,
or Ecliptic, all the year round, they divided up the neighbouring
stars into twelve constellations. This made it easier to keep
track of the months, seasons, and years. It also enabled them
to find the four critical days in which the seasons culminated.
Being Sun-worshippers, like nearly all the nations of antiquity,
they were very anxious to ascertain the exact date of the sab-
baths, new moons, equinoxes, and solstices ; for otherwise they
could not time their feasts, fasts, and sacrifices so as to have
them credited in the heavenly ledger. They regarded the Sun
as a Great Spirit labouring for the good of mankind, and fight-
ing the powers of cold and darkness with varying success. Each
summer he got the upper hand, but in the winter he lost his
strength, like his Semitic prototype, Samson, when he was shorn
of his flowing locks. As the very existence of the human race
depended on the Sun-God's success, the struggle was watched
with never-flagging interest and anxiety.
The year was then reckoned to begin in the spring, at the
time when the days and nights were equal. The Sun-God was
then in the centre of a group of stars which they pictured out
as a Bull (Taurus)}- At the longest day their God was in the
centre of a group which they named the Lion (Leo). At the
autumn equinox he was in the centre of a group which they
imagined to represent a Scorpion (Scorpio). And on the short-
est day in winter he was in the midst of a group which they
called the Water- Carrier (Aquarius).
1 Subsequent generations long inherited the tradition that each year was opened
by a bull with golden horns.
FIG. 63. SPIRAL NEBULA IN TRIANGULUM
Lick photograph.
V\BRT7>
Or TME
UNIVERSITY
or
CONSTRUCTION OF THE UNIVERSE 117
These significant symbols became famous in mythology, and
are several times mentioned in the Hebrew Bible and early
Christian writings. The brightest star in or near each of the
four groups has been known ever since as a " royal " star, though
its significance was lost when the Precession of the Equinoxes
dethroned the celestial Bull and set the heavenly Ram in the
place of honour. These royal stars were Aldebaran, Eegulus
Antares, and Fomalhaut.
The Zodiacal groups having been satisfactorily marked out,
the northern stars were made into a great winged Dragon
(Draco), which was supposed to guard the pole of the heavens. 1
The rest of the constellations were then figured off in other
parts of the sky. They were all connected together, each figure
forming a portion of the same great mythological sky picture.
As a rule they were all upright when on the meridian, either
north or south. 2
The picture-makers of 2800 B. a, looking south at midnight
at the spring equinox, imagined a huge man in the sky, crush-
ing a scorpion with his left foot, and strangling an enormous
serpent which was coiled around his body. The same observers,
on turning to the north, pictured a second man, kneeling on one
knee, and pressing the head of a winged dragon with the other
foot. 3 The stars which were faintly visible above the southern
horizon were afterward worked into the picture, and the knowl-
edge of it was handed down, from generation to generation, as
a divine revelation, to change or add to which would be sacrilege.
These picture-makers appear to have domesticated cattle,
sheep, goats, dogs, and horses. They hunted bears, lions, and
1 In after years the Precession of the Equinoxes made this winged dragon slip
off the pole of the heavens. He was then said to have been overcome by the
stalwart Michael and thrown into a pit that had no bottom. One rather lurid
writer tells us that "his tail drew the third part of the stars of heaven, and did
cast them to the Earth."
2 See the Constellation Chart at the end of this book.
8 The head of this winged dragon was then turned threateningly toward the
man, and had two bright stars for eyes. Its wings have since then been cut off,
in order to make room for other constellations. Its head has also been turned
around, for the same reason, so that its fierce basilisk stare has been lost.
118 HOW TO KNOW THE STARRY HEAVENS
hares, using bows and arrows, as well as spears. They do not
appear to have been acquainted with the tiger, elephant, camel,
hippopotamus, or crocodile. To their north lay a sea, and they
were familiar with ships and with sea-monsters. They sacri-
ficed on altars ; knew the stories of the Fall and of the Deluge,
and probably devised many of the constellations to keep record
of them.
These constellations became known to the Greeks. They are
described in a poem of Aratus (260 B. c.), and are mentioned in
the star-catalogue of Ptolemy (150 A. D.). In modern times
their religious significance has been lost. From time to time
their irregular and arbitrary boundaries have been changed, and
a number of other groups have been formed, to fill in the vacant
places. About 90 constellations are now recognised. 1
Most of the larger stars are known by names which were
given them by the Arab astronomers. Large numbers are dis-
tinguished by the genitive form of the name of the constella-
tion in which they occur, with a Greek letter prefixed to it.
Many thousands are known only by numbers in certain star-
catalogues. The great majority of telescopic stars have no
names at all.
It is not necessary to describe the constellations here, as they
are best studied by night, under the blue heavens, with an oc-
casional reference to a star atlas. The four star charts given
at the end of the book will be a help to beginners who live
in the Northern Hemisphere. One of them gives the North
Polar heavens, and the other three include all the Equatorial
constellations. In order to avoid confusion, no names or di-
visions are marked on these charts, but each one is accom-
panied by a key, giving all necessary particulars.
The first of the Equatorial Charts is intended to be used in
the spring (from December to March), the second in the sum-
1 Those interested in the ancient constellations should read an article by the
late Richard A. Proctor, in his "Myths and Marvels of Astronomy," and another
by E. W. Maunder (F.E.A.S.), entitled "The Oldest Picture Book of All," in
the "Nineteenth Century Magazine" for September, 1900.
FIG. 64. THE GREAT NEBULA IN ANDROMEDA
CONSTRUCTION OF THE UNIVERSE 119
mer (from April to July), and the third in the autumn (from
August to November). The Polar Chart can be used all the
year round.
In order to understand these charts, the learner should go
outside on a clear starlight evening, about nine o'clock, and
seat himself in a rocking-chair, facing the south. If he can tilt
the chair back against some trustworthy support, it will be an
advantage, as he may otherwise see the wrong kind of stars.
A dark lantern will be an assistance, to enable him to see the
charts and keys at intervals.
Let the beginner now select the Equatorial Chart which is
suitable for the time of the year. At the foot of the chart
he will find a number of dates. Selecting the date which comes
nearest to that of his observation, he will find that the stars
represented above it agree with those in the heavens in front of
him, from the horizon to the point overhead.
When the beginner wishes to identify the stars which are
farther north than the point overhead, he should take the Polar
Chart and turn it till the proper date is at the foot of the chart.
He can then lean well back in his chair, when he will be able
to recognise the resemblance between the brightest of the stars
above him and those represented on the chart. With the help
of the proper key the names of the stars and constellations can
be gradually and pleasantly acquired.
A good way to make a beginning is to get acquainted with
the names and positions of the brighter stars on clear evenings,
to divide them up into squares, triangles, etc., and then to fill
in with the fainter ones. After having done this in the Polar
regions, they can be connected with stars farther south, giving
particular attention to those on or near the Equator and Ecliptic. 1
1 The Equator can easily be found by fastening a stick or pointer to the top
of a fence, so that it points to the northwestern star in the Band of Orion, when
it is due south. All the Equatorial stars will occupy the same position when
they come to the local meridian. The Ecliptic can easily be found (approximately)
by noting the position of the Moon among the stars every night that it is visible.
The large planets are also on or near the Ecliptic. To prevent their being mis-
taken for stars it should be remembered that they do not twinkle, but shine with
120 HOW TO KNOW THE STARRY HEAVENS
In the course of a year the greater part of the heavens will
thus come under observation without the necessity of staying
up late at night. 1
Most of the stars in these constellations are only visually
connected, so that an observer in a distant solar system would
find them altogether differently arranged. There are many
natural groupings, however, like that known as the Pleiades,
and another including several of the brighter stars in the con-
stellation of the Great Bear. Such natural groups are being
discovered by the fact that the stars composing them are drift-
ing in the same direction and at the same speed.
Most of the telescopic star-clusters are evidently family
groups, as are also the thousands of double, treble, and quad-
ruple stars which revolve around their common centres of
gravity.
THE GALAXY
" A broad and ample road whose dust is gold,
And pavement stars." Milton.
The largest and most important structure in the visible Uni-
verse is that nebulous haze of invisible suns which is known as
the Via Lactea, the Galaxy, or the Milky Way. In fact, if the
Universe were no larger than the visible part of it, we might al-
most say that the Universe itself consisted of the Milky Way
and its appendages.
With the naked eye the Galaxy forms the most conspicuous
object of the midnight heavens. It is an irregular hazy ring
crossing the celestial sphere in a great circle. This circle is
like that containing the Signs of the Zodiac, but is very much
more tipped up with reference to the equator. A telescope of
a steady unflinching light. It will soon be found that they gradually change
their positions among the stars that lie near the Ecliptic.
1 "Astronomy without a Telescope," by E. W. Maunder, F.R.A.S., will be
found to make the subject more interesting. This may be followed by the study
of "Astronomy with an Opera Glass," and "The Pleasures of the Telescope,"
both bv Garrett P. Serviss.
CONSTRUCTION OF THE UNIVERSE
moderate power shows that it consists of a "blinding snow-
storm " of suns and star-clusters.
This Milky Way was formerly considered to form a kind of
irregular disc or " grindstone," with our Solar System not very
far from its centre. More accurate observations, however, have
caused this theory to be discarded. It is now believed to con-
sist of long spiral wisps or serpent-like streams of nebulous
haze, of more or less circular section, and considerably distorted
by projection. In one place the main stream splits in two, but
finally comes together again. This split portion has a number
of narrow nebulous channels crossing the dark interval which
separates them, and dividing it into irregular islands, or " coal-
sacks." If we were on one side of this Milky Way, instead of
being inside it, we should probably see it as a vast ring-like spiral
nebula, with its centre of rotation still comparatively empty.
If the observer is favourably situated, nearly all of the Milky
Way may be seen from one .station in the course of a long
winter night. Such an observation will soon show that, al-
though very irregular, these " flowing robes of infinite space "
form, on the whole, a nearly complete girdle around our part of
the Universe.
With a telescope it is easily seen that the Galaxy consists
of an innumerable host of telescopic stars, promiscuously dis-
tributed, with thicker clusters or aggregations here and there
(see Figures 47, 48, and 61). Even the naked-eye stars (with
the exception of the nearest) are found to be most numerous in
and around the Milky Way, and to thin out gradually as we
approach its poles on either side. The same is true of the
stellar nebulae. The entire visible system probably resembles
a watch in shape, slowly rotating on its axis, and condensing
into a flat spiral disc.
THE NEBULA
While it is found that the stars and stellar nebulae are most
numerous near the Milky Way, it is rather startling to find
that with the Gaseous Nebulae the reverse is true. There are
HOW TO KNOW THE STARRY HEAVENS
very few of them in or near the Milky Way, and they increase
in numbers toward its poles.
The Magellanic Clouds, in the Southern Hemisphere, greatly
resemble the Milky Way in appearance ; but, instead of being
composed of stars and stellar nebulae, they consist of stars and
gaseous nebulae.
Some nebulae are diffuse and sprawling, as though the central
attraction was not strong enough to draw them together or had
been overpowered by some outside influence. One of them has
been traced along the starry sphere for a length of 8 degrees.
Supposing that its distance from us is only two million times
the Sun's distance (and it can hardly be less), it must be as
long as from here to the nearest star. Though many of the
gaseous nebulas are of enormous thickness, they all appear to
be transparent.
The late Professor Keeler, a short time before his death,
found that the telescopic camera showed twenty times as many
nebulae as the telescope alone. The number within the range
of the photographic telescope is now put at 120,000 or more,
and the majority of them are more or less spiral, like those
represented in Figures 63 and 85.
The Great Nebula in Andromeda has a condensed nucleus
(giving a continuous spectrum) surrounded by a swirl of nebu-
lous matter. In fact, it looks not unlike the planet Saturn
surrounded by its rings (see Figure 64). It is, however, im-
mensely larger than our entire Solar System, and is probably a
galaxy of suns.
When a spiral nebula is turned edgeways to us, it is not
recognisable as a spiral, but has a more or less lenticular shape
(see Figure 65). The remarkable Ring Nebula in Lyra re-
sembles in telescopic appearance one of the familiar vortex
rings which occasionally rise from the smoke-stack of a steam-
engine. Like most of the ring-nebulae, it has a faint star in its
centre. But photographs recently taken by Professor Schae-
berli at Ann Arbor, Michigan, show that a two-branched spiral
originates at and surrounds this central star. The visible nebu-
FIG. 67. THE TRIFID NEBULA IN SAGITTARIUS
Composed of glowing gas. The rifts were probably caused by stars drifting through
body of nebula.
CONSTRUCTION OF THE UNIVERSE
lous ring is the most prominent part of this double spiral (see
Figure 66).
Other nebulae have very irregular outlines, at some places clean
cut, and elsewhere fading gradually away. Some are split up
by sharp fractures, as though they had been torn asunder by
some wandering star drifting through them. Such is the Trifid
Nebula in Sagittarius (see Figure 67). The Great Nebula in
Orion also has some of these peculiarities, and has several nebu-
lous stars connected with it. Its present irregular outlines may
be partly due to the disrupting influence of these stars, or it is
possible that the neighbouring nebula may have collided with
it. Seen through a powerful telescope, it forms one of the most
magnificent objects in the heavens. Its real size is so enormous
that the mind cannot realise its vastness. It has been estimated
that if a million discs as large as the orbit of Neptune were
placed in front of the nebula, they would not be sufficient to
hide it from us. The spectroscope shows that the matter com-
posing it is in the form of gas so diffuse as to be almost a
vacuum (see Figure 68).
It was formerly supposed that all nebulae are at an intense
heat, causing the peculiar glow which makes them visible to us.
It seems probable, however, that the more diffuse of them are
at the temperature of space ( 230 F.), and that their light is
an electrical phenomenon due to a rain of negatively charged
particles driven off from the stars (in the form of coronas) by
the repulsive action of light. This would explain the simple
nature of their spectra, as the glow would be chiefly confined to
the surface, where the lighter gases, like hydrogen and helium,
collect.
UNSOLVABLE PROBLEMS
Although a great many facts bearing on the distribution and
relationships of the visible stars and nebulae have been discov-
ered in the last few years, we are not yet in a position to give
a satisfactory answer to the questions asked in the quotation at
the beginning of this chapter. At present we can only say, with
the late Richard A. Proctor :
124 HOW TO KNOW THE STARRY HEAVENS
"The sidereal system is altogether more complicated and more
varied in structure than has hitherto been supposed : in the same
region of the stellar depths co-exist stars of many orders of real mag-
nitude ; all the nebulse, gaseous or stellar, planetary, ring-formed,
elliptical, and spiral, exist within the limits of the sidereal system ;
and, lastly, the whole system is alive with movements the laws of
which may one day be recognised, though at present they are too com-
plex to be understood."
The Universe is so vast that a bird's-eye view of it cannot be
obtained from a single standpoint, and though that standpoint
is being swept along through the lofty corridors at a speed fifty
times as great as that of a cannon-ball, the life of the human
race is hardly long enough to profit by the change of position.
We are like the man in the forest who said that he could not
see the wood for the trees. Even in those parts where we
imagine that we can see a limit to the celestial forest, we can-
not be sure that it is not a mere clearing in the woods, or a gap
between our forest and the next one. And the situation is com-
plicated by the fact that the celestial trees are not anchored fast
to a visible ground, but are drifting around in all directions,
while we are prisoned on a conveyance whose movements we
are utterly unable to control.
To use the simile of Sir Isaac Newton, we can learn some-
thing of the celestial pebbles that lie around us, but the great
ocean is beyond. The finite cannot grasp the infinite, nor can
the ephemeron comprehend the eternal. And if it could, what
then?
FIG. 68. GREAT NEBULA IN ORION
Lick photograph.
Irregular mass of glowing gases. Many millions of times larger than Solar System.
Irregularities possibly due to collision with neighbouring nebula.
CHAPTER XI
SOLAR ARCHITECTURE
"We know the Sun to be infinitely more complex in structure . . . than it
was formerly supposed to be. ... We have learned that . . . the glowing veil
of air hides by day . . . the largest (though not the most massive) part of that
Sun." Richard A. Proctor.
THE individual construction of the stars themselves can
best be found by studying our Sun and comparing its
peculiarities with those of more distant suns. This comparison
has led to the discovery that no two stars are at precisely the
same stage of evolution.
INTERIOR OF SUN
Our Sun appears to be still gaseous with heat, from centre to
circumference. But its constituent gases are so compressed by
the attraction of its huge mass, that it is, on the average, denser
than water. It has in fact the density of a liquid with the
mobility of a gas. In other words, it is composed of glowing
"gaseous-liquids," the central layers of which are extremely
dense (for gases), while the outer layers are only moderately so.
The gaseous-liquid nature of the interior is shown by the
average density of the Sun, which is 1.4 that of water. This is
about what might be expected for a huge mass of intensely hot
gas, but is far too small for solids or liquids, taking into con-
sideration the fact that solar gravitation is more than 27 times
as great as that of the Earth.
That the interior is not solid may also be seen from the fact
that the surface heat is kept up by a continuous supply of hot
material from below. This interior heat is actually due to the
contraction or shrinkage of the outer layers of the Sun as they
126 HOW TO KNOW THE STARRY HEAVENS
cool off. The whole Sun may be said to boil, the hot gases
forcing their way (explosively or otherwise) to the surface, cool-
ing off somewhat, and then sinking. If the interior were solid,
or if a solid crust were to form, this " boiling " circulation would
cease, the heat would not be so free to rise, and the surface
would lose its heat and become dark. Some day this will take
place, and we shall then have to look for another source of heat,
or get used to the intense cold of interstellar space.
This is the period referred to by George Sterling when he
says:
" The Night inevitable waits
Till fails the insufficient Sun,
And darkness ends the toil begun
By Chaos and the morning Fates.
" And star ward drifts the stricken world,
Lone in unalterable gloom,
Dead, with a Universe for tomb,
Dark, and to vaster darkness whirled."
The Testimony of the Suns.
Judging from the Sun's outer characteristics, it is almost cer-
tain that there are no compound substances in its interior. It
is even possible that the so-called elements themselves are dis-
sociated, by the intense heat, into one primitive form of matter,
which exists only in the gaseous-liquid state.
THE PHOTOSPHERE
The solar photosphere is a dazzlingly incandescent globular
shell surrounding and concealing the main body of the Sun. It
is indeed the only part of the Sun which is usually visible to
us. It is composed of closely packed clouds of intensely hot
metallic vapours.
These photospheric clouds are probably long and pillar-like,
floating upright in the metallic atmosphere of permanent gases
which surrounds the main body of the Sun. Under ordinary
circumstances only the bright tops of these radial clouds are
visible to us. As the spaces between them are comparatively
SOLAR ARCHITECTURE 127
dark, the result is that the entire surface of the Sun has a
granulated or mottled appearance when seen through a power-
ful telescope. It looks, indeed, like a piece of grey cloth stretched
over a hoop, with rice-grains or snowflakes thickly scattered
over it.
The particles composing these upright floating clouds probably
rise (in a gaseous state) from the inconceivably hot interior of
the Sun, and gradually cool off' through expansion and outward
radiation. At a certain elevation the diminished pressure and
temperature cause them to condense into the brilliant vaporous
clouds whose tops form the visible photosphere.
As the rising, cooling, and condensing processes go on all
around the solar nucleus, there is probably a continuous del-
uge of white-hot metallic " rain " descending Sunward from the
chilled summits of these radial luminous clouds.
It is possible that in the case of refractory elements like car-
bon, calcium, etc., the liquid drops " freeze " and descend in a
"hailstorm" of genuine diamonds and solid metal shot. If
this is so, it is evident that the falling " hail " will be remelted
and vaporised as soon as it reaches a sufficiently hot layer of
gases. The extraordinary brilliancy of the solar photosphere
may be largely due to the clash of these diamonds and metal-
lic shot, as they fall back in a continuous incandescent hail-
storm onto the ascending gases beneath them.
FACUL.E AND SUN-SPOTS
The intense activity of internal physical action is sometimes
indicated by the appearance of certain dark blotches on the
otherwise fair face of the photosphere. These are commonly
known as Sun-spots, and are usually surrounded by brilliant
eruptive patches of piled-up photospheric clouds or faculce.
The Sun-spots are more or less irregular black hollows which
occasionally form in the cloudy photosphere on each side of the
solar equator, and are seen to drift around as the Sun rotates
on its axis (see Figure 24). They are most abundant at rather
irregular intervals of about eleven years. At the beginning of
128 HOW TO KNOW THE STARRY HEAVENS
one of the Sun-spot periods the spots are some distance north
and south of the Equator. Later on, the Sun-spot areas move
nearer to it, so that the last spots seen, in one such period, are
not far from the Equator.
The Sun-spots usually break out in the midst of a piled-up
mass of brilliant faculce. At first they appear as irregular black
openings in the bright photosphere. They gradually increase in
size and become more circular in outline. The lower ends of
the long perpendicular clouds which (presumably) compose the
surrounding photosphere gradually drift into the opening, so that
the spot becomes a saucer-shaped depression. The black bottom
of this saucer is known as the Sun-spot nucleus, and the semi-
dark fringed sides form what is known as the penumbra.
The nucleus itself is sometimes 40,000 to 50,000 miles in
diameter, the surrounding penumbra being occasionally 150,000
miles across. 1
Sun-spots vary in depth from 500 to 2,000 miles, and are
filled with cooler and therefore less luminous gases, which ab-
sorb the light from below. The blackness is only the result of
contrast, for their gaseous contents are really hotter and brighter
than molten steel. There appears to be a spiral uprush of hot
gas all around the spot, with a descending current in the mid-
dle. They are evidently related to the cyclones, tornadoes,
etc., in the temperate regions of our Earth. The surrounding
penumbra consists of jets, swirls, and cataracts of luminous
vapour surging into the abyss. Long plume-like " bridges " of
superheated gas occasionally shoot out from the sides and cross
the cavity, which is finally covered up by dazzling masses of facu-
Ise (see Figures 25 and 69). When these brilliant inrushes of
vapour are crossing the abyss, they produce an electrical activ-
ity which extends far out into space. On our Earth it produces
the polar phenomena known as the Aurora, and causes power-
ful currents in all kinds of electrical apparatus. These latter are
commonly known as electrical storms.
1 If the great Sun-spot of 1858 had been 35 times larger, it would have cov-
ered the entire surface of the Sun, and practically put it out of business for the
time, so far as illuminating and heating purposes are concerned.
SOLAR ARCHITECTURE 129
ROTATION
An examination of the time which it takes the spots and
granulations of the photosphere to move across the disc as
the Sun rotates shows that the clouds at a distance from the
Equator take a longer time to complete a rotation than those
on or near to the Equator. While the Equatorial granulations
rotate in 25J days, the spots take more than a day longer to
complete their rotation. And the granulations near the Poles
take about 40 days to go once around. This shows the gaseous
mobility of a great part, and probably of the entire mass, of the
Sun.
THE CHROMOSPHERE
I have said that the dazzling white clouds which form the
visible photosphere float in an atmosphere of uncondensed gases.
This metallic atmosphere, or veil, is ruddy, but tolerably trans-
parent. It extends 4,000 or 5,000 miles above the luminous
clouds, and has a ragged storm-tossed surface (see Figure 27).
It is known as the chromosphere, sierra, or solar atmosphere,
The lower portion of it (about 500 miles thick) is known as
the " reversing layer." a The spectroscope has shown that this
lower and denser portion consists of metallic gases,- with some
non-metallic elements, all free and uncombined on account of
the intense heat. The most abundant (or at least the most
recognisable), are hydrogen, calcium, iron, manganese, nickel,
and titanium. The following are also present : barium, carbon,
chromium, cobalt, germanium, helium, magnesium, platinum,
silicon, silver, sodium, and zinc. There is also strong evidence
of the presence of aluminium, cadmium, copper, lead, molybde-
num, oxygen, palladium, uranium, and vanadium.
In addition to these elements, there are lines indicating the
existence of substances as yet unknown on Earth.
1 This name is derived from the fact that a spectrum formed from its light alone
has the usual dark solar absorption lines reversed into bright radiation lines. This
' ' flash spectrum " can be obtained for only a few seconds at the beginning or end
of a solar eclipse.
9
130 HOW TO KNOW THE STARRY HEAVENS
There are no signs of chlorine, nitrogen, gold, mercury, phos-
phorus, sulphur, and some other elements. This does not,
however, prove that they are not present in other parts of the
Sun.
The upper and thinner portion of the sierra does not contain
the numerous metals found in its lower " reversing layer." It
is composed of hydrogen, helium, and one or two other perma-
nent gases. 1
ERUPTIVE PROMINENCES (METALLIC FLAMES)
In the Sun-spot zones on either side of the Equator, immense
red jets of glowing gas rise between the white clouds of the
photosphere, pass through the sierric atmosphere, and extend
many thousands of miles above it. They are known as eruptive
prominences or metallic flames (see Frontispiece and Figures 26,
27, and 70). The highest one ever seen rose more than
350,000 miles above the general surface.
These red metallic flames are best seen when on the edge of
the Sun. When they are on our side they are invisible with
the telescope, but their upper surfaces can be photographed (at
different elevations) with the aid of Professor Hale's spectro-
heliograph. In this position they are known as Eruptive Cal-
cium Flocculi (see Figure 128).
These eruptive flames, or flocculi, consist chiefly of gaseous
calcium, hydrogen, sodium, magnesium, and iron. They ap-
pear to be forced up by explosive physical changes below the
photosphere, but their great elevation is probably due to the re-
pulsive action of light on the small particles of which they
consist.
CLOUD PROMINENCES (HYDROGEN FLAMES)
Above the sierra or chromosphere there are also to be seen huge
ruddy clouds consisting of hydrogen and helium. When they
are seen in profile, at the edge of the Sun, they are known as
1 The non-metallic elements are here printed in italics.
SOLAR ARCHITECTURE 131
cloud prominences or hydrogen flames. When they are on
our side of the Sun, and are photographed from overhead
by means of the spectroheliograph, they are called hydrogen
flocculi. 1 They are not confined to latitudinal belts or zones,
like the eruptive ones just mentioned, but are to be found over
all parts of the Sun's surface. There does not seem to be any
atmosphere for them to float in. Like the eruptive prom-
inences, they appear to be composed of extremely small particles
of matter, upborne by the repulsive action of the Sun's light.
FIG. 71. A SOLAR "CLOUD" OF GLOWING HYDROGEN
(PROFESSOR YOUNG)
About 100,000 miles long and 54,000 miles high. Notice the
bright uprush below one end of it.
In 1871 Professor Young observed a hydrogen cloud about
100,000 miles long, with its summit about 54,000 miles above
the sierra. It was connected with this latter by a number of
vertical columns that looked like water-spouts (see Figure 71).
Thirty-five minutes later the cloud had been blown to pieces
by an eruption, and the fragments were scattered to a height of
207,000 miles (see Figure 72). They gradually faded away as
they rose, leaving an eruptive prominence 50,000 miles in height
(see Figure 73). The flame-like summit of this eruptive mass
rolled over like a breaking wave (see Figure 74), and in a few
minutes faded out of sight. These changes all took place in
about two hours.
1 For further particulars concerning the spectroheliograph and the latest
results obtained with its aid, see an illustrated article by Professor Hale in the
"Popular Science Monthly," for May, 1904.
132 HOW TO KNOW THE STARRY HEAVENS
THE CORONA
The white spherical cloud-surface of the Sun has now been
described, and also the ruddy atmosphere and the two kinds of
prominences which rise
from it. But outside of
all these there is a ra-
diating halo of pearly
light sometimes ex-
tending more than
2,000,000 miles in every
direction (see Figures
26, 28, and 75). This
is known as the corona.
Like the eruptive prom-
inences, it appears to
start from volcanic
outbursts; but, its
particles being smaller,
instead of being merely
upheld by the radiant
energy of the Sun, they
are violently repelled,
so that they stream
forth continuously and
pass away into outer
space. When Sun-
spots are numerous, the
visible corona does not
extend so far as when they are absent or scarce. The greatest
development of the corona is over the Sun-spot zones north and
south of the Equator. The rotation of the Sun causes the
coronal streamers to bend in a plume-like manner. They are
not so crowded together near the poles of the Sun, so that
the polar streamers are very distinct (see Figure 29).
When the spectroscope is turned to this coronal halo it shows
a continuous spectrum crossed by bright lines. The former
FIG. 72. THE SAME REGION 35 MINUTES LATER
(YOUNG)
Rising wisps of glowing hydrogen, reaching a height
of 207,000 miles. The eruptive mass below is growing
larger.
FIG. 70. SOLAK "FLAMES" OR PROMINENCES
By Zoellner. (From Comstock's " Text-book of Astronomy," published by
Messrs. D. Appleton & Co. )
FIG. 76. THEORETICAL SECTION OF SOLAR PHOTOSPHERE
By Trouvelot.
Clouds of carbon, etc., floating in an atmosphere of metallic gases. Hot gases from
interior forcing their way out. (From Todd's " New Astronomy,"
published by The American Book Co.)
SOLAR ARCHITECTURE
133
FIG. 73. THE SAME REGION 35
MINUTES LATER (YOUNG)
The uprush has developed into a mass
of rolling and ever-changing "flame,"
50,000 miles in height.
indicates the presence of solid or liquid particles, and the
bright lines are those of glowing hydrogen gas. There is also
a bright green line due to an
unknown gas which has been
provisionally named "coro-
nium." The atoms of these sub-
stances are so far apart that the
corona is practically a vacuum.
SOLAR ENERGY
As in the lime-light, or oxy-
calcium lamp (used for magic
lanterns, etc.), the brilliancy of
the Sun's photosphere is largely
due to incandescent calcium.
The intense bluish-white light
of this hollow cloudy sphere
forces its way through the ruddy transparent atmosphere and
prominences. In doing so it loses much of its intensity and
becomes slightly yellow.
It passes through the
coronal streamers with
but little loss, and
spreads out evenly in
all directions.
The planets catch a
little of this scattered ra-
diance, but the bulk of
it is lost in the outer
darkness of space. If
the portion of light and
heat received by the
Earth be represented by
the figure 1, the part
which misses the Earth will be represented by 2,200,000,000.
So that what we get is equal to one cent out of twenty-two
F IG . 74. _ THE SAME, 15 MINUTES LATER
(YOUNG)
In half an hour this curling prominence faded entirely
away.
134 HOW TO KNOW THE STARRY HEAVENS
millions of dollars. What all the planets catch is equal to ten
cents out of the same amount of money. All the rest escapes
into outer space and is apparently wasted.
The amount of " waste " may be conceived from the fact that
(in spite of the loss by absorption in passing through the sierra,
etc.) every square foot of the Sun's surface continually sends
out into space about 10,000 horse-power of radiant energy,
while a square foot of our Earth's surface receives about a
quarter of one horse-power. 1
CAUSE OF SOLAR HEAT
Although we cannot see what is taking place beneath the
photosphere of the Sun, we can learn something of its anatomy
and physiology by indirect methods. All the surface phenom-
ena, revealed by the telescope and spectroscope, are due to
deep-seated mechanical and physical processes. Our knowledge
of the effects of known mechanical and physical laws enables
us to form some idea of what is going on below. The whole
body of the Sun appears to be composed of concentric gaseous
layers, like the coats of an onion. Each shell is denser than
the layer above it, and therefore thinner than the one below.
As the outer layers cool off by the radiation of their heat into
space, they settle down onto the lower layers and urge them to
a quicker rotation. This makes the Sun a huge electrical
machine, generating an enormous amount of energy, which
manifests itself in different forms. When the various layers
have reached a certain density, there is a periodical overheating
of the lower layers through the progressive cooling of the upper
ones. This periodical overheating causes the layers to react
on one another with great violence. The overheated gases
escape at every weak place, and these periodical outbursts of
energy are visible on the surface in the form of eruptive promi-
nences, Sun-spots, etc. (see Figure 76).
1 This latter would in one year lift GO short tons one mile high ; the former
would lift 40,000 times as much.
SOLAR ARCHITECTURE 135
So much for the physical constitution of the Sun. If the
reader will now turn back to the section entitled " Classes of
Stars," in Chapter VIII, he will be able to form some idea as to
the physical condition of nebulae, stars, and planets, at different
stages of evolution.
OLD AND DYING SUNS
The common variability of red stars is evidently the outer
manifestation of the death-struggles of old and waning suns.
The vital forces of the aged stars are no longer able to prevent
the various elements from forming chemical combinations,
resulting in periodic fluctuations. Their interior forces are
making tremendous but unsuccessful efforts to throw off the
cooling vapours above, which are gradually choking the life out
of the dying suns. Some of them are nearly invisible, except
when these paroxysms are at their height. During these peri-
odical spasms, they glare out strangely into the darkness for a
time, and then subside. Their struggles grow feebler as time
goes on, and finally their uneasy flickering subsides into the
calmness and tranquillity of solar death.
CHAPTER XII
A REELING WORLD
" Learned Faustus,
To know the secrets of astronomy,
Graven in the book of Jove's high firmament,
Did mount himself to scale Olympus' top,
Being seated in a chariot burning bright,
Drawn by the strength of yoked dragons' necks.
When Faustus had with pleasure ta'en the view
Of rarest things, and royal courts of kings,
He stayed his course and so returned home ;
Where such as bare his absence but with grief,
I mean his friends and near'st companions,
Did gratulate his safety with kind words,
And in their conference of what befel,
Touching his journey through the world and air,
They put forth questions of astrology,
Which Faustus answer'd with such learned skill
As they admir'd and wonder'd at his wit."
Marlowe, ' ' Faustus. "
A BIRD'S-EYE VIEW
IN order to ascertain some more particulars about our own
Earth, let us go back, for a time, to our Chariot of Imagi-
nation, and once more watch our Solar System from a short
distance away.
Let us suppose that we are so situated in space that the Sun
and planets appear as though they were floating in front of us,
on the surface of a sheet of perfectly clear water. And let us
suppose that (owing to a slight eddy in the water) the planets
are all circling slowly around the Sun. When they are between
us and the Sun, they drift to the right, but when they are beyond
it they go to the left. The surface of this imaginary sheet of
A REELING WORLD
137
water will, to an inhabitant of the Third Planet, represent the
plane of the Ecliptic, the so-called path of the Sun.
From our supposed position in space, we can not only see our
own Solar System spread out before us, but also, in the far dis-
tance, the innumerable starry systems which surround it. Those
Pisces.
FIG. 77. DIAGRAM ILLUSTRATING ZODIAC
stars which are on or near the horizon of our imaginary sheet
of water may be conveniently divided into twelve equal groups
or constellations. 1
Among these twelve Signs of the Zodiac, or Ecliptic, are
those which bear the names of Sagittarius, Virgo, Gemini, and
Pisces. As these constellations will hereafter be used to indi-
1 Named as follows :
1. Aries, the Ram. 5. Leo, the Lion. 9. Sagittarius, the Archer.
2. Taurus, the Bull. 6. Virgo, the Virgin. 10. Capra, the Goat.
3. Gemini, the Twins. 7. Libra, the Balance. 11. Aquarius, the Water-Bearer.
4. Cancer, the Crab. 8. Scorpio, the Scorpion. 12. Pisces, the Fishes.
138 HOW TO KNOW THE STARRY HEAVENS
cate planetary motions, their relative positions on the Ecliptic
are here indicated (see Figure 77).
Keeping these positions in mind, let us now turn our eyes
back to our own Solar System.
If we get out our telescopes and watch the Third Planet, which
is now known to us as the Earth, we shall see that its North
Pole is uppermost, but that it has a heavy list to the right. As
the globe spins around, the markings on its near side move to
the right, with a slight downward tendency due to the planet's
inclination.
One result of the planet not floating quite erect is that the
rotation causes its tropical regions to be continually dipping
into the water and emerging from it, while the rest of the globe
remains all the time either above or below the surface, which
represents the plane of the Ecliptic.
On turning to the other planets for comparison, we find that
they are rotating in the same direction. Some of them have
satellites, or moons, and these appear to drift around their
primaries in the same direction, as though the rotation of each
planet caused a secondary eddy in the water. It will be seen,
therefore, that all these movements (1) the revolution of the
planets around the Sun, (2) their rotation around their axes, and
(3) the revolutions of the satellites around their primaries are
in the opposite direction from that taken by the hands of a
watch. 1
A closer view of the satellites would show that their rotation
also agrees in direction with the three motions just described.
Some of the satellites have adjusted the speed of their rotation
to that of their revolution, so that they always show the same
side to the world they attend. 2
It is hardly necessary to say that all these agreements are not
1 The satellites of the two outside planets do not at present conform to the
general rule, though they probably will in the course of time. These planets ap-
pear to have been formed later than any of the others.
2 The two inner planets appear to have done the same thing, so that they
always turn the same side to the Sun.
A REELING WORLD 139
accidental. There is a cause for them, as will be seen in a later
chapter.
If we stay where we are, and watch the movements of the
Earth for a few years, we shall see that while it drifts around
the Sun its axis keeps the same position. The result is that a
person living at the North Pole would have the same star over-
head all the year round.
When the Earth is to the right of the Sun, it is obvious that
the North Pole is in the dark, and that it is winter in the North-
ern Hemisphere (see Figure 12). When the Earth gets beyond
the Sun, both poles are just lighted up by it, and the days and
nights are equal all over the globe. This is known in the North-
ern Hemisphere as the Spring Equinox. When it arrives at
the left of the Sun, the North is enjoying its summer, and the
South Pole is in the dark. Finally, when the Earth reaches
our side of the Sun, the days and nights are again equal all
over the globe. This is known in the North as the Autumnal
Equinox. As already stated, the axis of the Earth does not
share in any of these movements of the planet, but remains fixed
with regard to the stars.
Let us now see what ideas the inhabitants of this Third Planet
are likely to have with regard to the various movements just
described. The rotation of the planet itself they will not be
able to perceive, so that, as it spins toward the east, they will
naturally fall into the delusion that the stars themselves are roll-
ing over toward the west. They will also naturally think that
the Sun and planets are doing the same thing. But as they are
also ignorant of the fact that their Earth is leaning over to one
side, they will be surprised and puzzled to find that the Sun
gradually drifts toward the north and south as summer and
winter approach. They will also find it hard to account for the
erratic manner in which the planets appear to move, or for the
fact that they always keep on or near the Sun's path.
To an outside observer these circumstances seem to be too
simple to require explanation, but to an inhabitant who can
neither see, hear, nor feel that his own world is moving, the
140 HOW TO KNOW THE STARRY HEAVENS
whole of the celestial motions are puzzling to the last degree.
It speaks well for the intelligence of the inhabitants that many
of them have at last managed to find out the real facts of the
case.
As the Earth rolls over every day there are two points on the
surrounding " star-sphere " which, to an inhabitant of the planet,
do not appear to move, but seem to be centres of rotation. These
two points are opposite the North and South Poles of rotation.
If we let the eye follow the direction of the axis, in an upward
(but slanting) direction, till it reaches the stars, it will be found
that there happens to be a tolerably bright star near the point
around which the other stars appear to move. To an inhab-
itant of the Earth this star therefore becomes known as the
North Pole-Star. Let us keep this in mind, for if the axis of
the Earth never changes its position this star will always re-
main the North Pole-Star so far as the Earth is concerned. 1
There is another peculiarity about the Earth's motions that is
worth mentioning. The World, like all the other planets, does
not go around the Sun in an exact circle, but in a nearly circular
ellipse or oval. The result of this is that at one part of the
year the Earth is about 3,000,000 miles nearer to the Sun than
it is six months earlier or later.
From our chosen point of observation the Earth is to the
right of the Sun on the 21st day of December in each year, and
its North Pole is then turned exactly away from the Sun. This
part of the Earth's orbit is termed the Winter Solstice, and we
will call it the point A. From the Earth, the Sun then
appears to be in the sign or constellation of Sagittarius (see
Figure 77).
A few days later the Earth reaches that part of its orbit where
it is nearest to the Sun. This part of the orbit is termed its
Perihelion, and we will call it the point B.
1 In "Julius Caesar," Shakespeare makes one of his characters say:
" I am constant as the Northern Star,
Of whose true-fixed and resting quality
There is no fellow in the Firmament."
A REELING WORLD 141
OUR FIRST VISIT (A.D. 1900)
Let us note the relative position of these two points in the
year 1900 A.D. (10 apart, measured from the Sun). Then we
will wait for a few thousand years, so as to see whether the two
phenomena always continue to happen in the same places.
SECOND VISIT (A.D. 8400)
After amusing ourselves by travelling among the stars for
6,500 sidereal years we return to our System (in the year 8400
A. D.), and look for the Third Planet. It is still spinning away
like a top that is wound up for ever. But, strange to say, there
has been a remarkable change in the position of the two points
A and B. The northern end of the polar axis, instead of point-
ing away from the Sun when the Earth was to our right (see
Figure 12), has reeled slowly back (or retrograded) through a
quarter circle. Its opposition (A) to the Sun, therefore, takes
place when the Earth is between us and the Sun. If we regard
the Earth as the hand of a watch (going around the Sun once a
year, the opposite way to the hands of our watches), it is evi-
dent that this watch has gained a quarter of a year (90 of arc,
measured from the Sun). For the inhabitants will tell you that
it is the 21st day of December, while it is evident that it ought
to be the 22d of September so far as the earthly revolutions are
concerned.
The result of this is that the Earth has now another Pole-Star,
and the old one appears (to the creatures on the Earth) to go
circling around it like all the other stars. The twelve monthly
" mansions of the Sun " have also swung a quarter round, so that
they are occupied by different sets of stars. From the Earth,
the December Sun now appears to be in the constellation of
Virgo instead of being in Sagittarius as before (see Figure 77).
Let us see whether there has been any change in the peri-
helion (B), the place where the Earth is nearest to the Sun. Yes,
it has moved forward in the orbit about 20 of arc. The two
points A and B, which were only 10 apart, are now 120 apart
142 HOW TO KNOW THE STARRY HEAVENS
(10 +90+20=120 ). The combined result of the two changes
is that, instead of being nearest to the Sun at the beginning of
January, the Earth is now in perihelion toward the end of
April.
THIRD VISIT (A.D. 14900)
Let us now go away a second time for 6,500 years, and then
come back to our Solar System again (in the year 14900 A. D.).
The points A and B have gone on separating at the same
rate, so that the angle between them is now 230 of arc (10+
110 +110 = 230 ), measured, as before, from the Sun. It is
therefore December 21 when the Earth is to the, left of the Sun.
A third and distant Pole-star has replaced the second one. The
December Sun is now in the constellation of Gemini, and the
Earth is nearest to the Sun in August.
FOURTH VISIT (A.D. 21400)
A third time we retire for the same length of time, and then
go back to our old acquaintance (A. D." 21400). By this time
the Earth-clock has gained three quarters of a year with refer-
ence to the stars, or nearly a year with reference to its peri-
helion (10+110 +110 +110 = 340). The Earth is now beyond
the Sun in December. A fourth Pole-star has replaced the
third one. The December Sun is now in the constellation of
Pisces, and the Earth is again nearest to the Sun in December.
FIFTH VISIT (A.D. 27900)
Once more we go away for the same length of time. On our
return (in the year A.D. 27900), the points A and B have passed
each other. The Earth-clock has gained a whole year with
reference to the stars, so that the inhabitants tell us we are a
year overdue. December 21 has at last reached its old camping-
ground to the right of the Sun (as in Figure 12). The old Pole-
star, that we knew so well 26,000 years ago, has returned to its
place of duty. And so have the twelve Signs of the Zodiac, so
that the December Sun is once more in the constellation of
A REELING WORLD
143
Sagittarius. But the points A and B are now 90 apart, so that
the Earth, instead of being nearest to the Sun at the opening of
the year (as at our first visit, in the year A. D. 1900), does not
reach its perihelion until March. Figure 78 shows the posi-
tions of A and B at the various dates mentioned.
FIG. 78. DIAGRAM ILLUSTRATING PRECESSION OP EQUINOXES AND
ADVANCE OF PERIHELION
The places marked A 1, 2, 3, 4, 5, are the positions of the Earth at the Winter
Solstice, at the dates mentioned. The places marked B 1, 2, 3, 4, 5, are the posi-
tions where the Earth is nearest to the Sun at the dates mentioned.
We have now followed the backward reeling of the Earth's
axis for one complete re volution, which has taken 26,000 years. 1
This reeling of the Earth's poles around the poles of the Ecliptic
is known as the Precession of the Equinoxes, because it makes
1 More exactly, 25,868 years.
144 HOW TO KNOW THE STARRY HEAVENS
the spring and autumn equinoxes come a little sooner every
revolution than they would otherwise do. It is in some respects
similar to the slow wabbling motion of a child's top. We may
almost say that our World is a big top which spins and wabbles
as it swings around the Sun. 1
EIGHTEENTH VISIT
If we were to keep up our periodical visits to the Earth till
the point B, where it is nearest to the Sun, has advanced one
complete revolution to its old place, it would take about 13 more
visits, 6,500 years apart. For this point, called the Earth's
perihelion, takes 109,000 years to complete its circuit.
MILLIONS OF YEARS LATER
Suppose that we now leave our System for say x millions
of years and then come back to it. What changes shall we
find on our return ?
In the first place we shall have some trouble in finding our
Solar System at all, for in the meantime it has drifted so far
that, if its curved path were straightened out, it would be equal
in length to Sx times the distance of Sirius. And its Sun has
changed from a yellowish-white star to a dark-red one, with
periodical spasms of brilliancy.
In the second place, when we have found it, picked out the
wizened relic of our once-beautiful Earth, and taken our star-
photographs, we shall discover that the almost inperceptible
drifting of the stars has by this time completely changed the
face of the heavens. The " sweet influences " of the Pleiades
(Job xxxviii, 31) have now been dissipated and lost. The
" Bands of Orion " are loosed for ever. The " Mazzaroth " (or
Signs of the Zodiac) are no more waiting to be led forth in
their season. And the Great Bear, with her cub, no longer re-
mains to be led around the " pole." Of all the constellations
1 The cause of the Precession of the Equinoxes will be dealt with in chapter
XV.
A REELING WORLD^ 145
we used to know so well, not one is now recognisable, though
myriads of shining suns still sparkle in the ebon " vault."
On this our last visit to the Solar System we not only find
that the Sun has changed its colour and lost much of its former
size and brilliancy, but that the planets are not in the same
condition they were in before. The Third Planet, for example,
rotates very much slower than it used to, and its Moon is farther
from it. The result is that the Earth's day and month are now
the same length (equal to about 57 of our days). The Moon
still shows but one side to the Earth, and the Earth now shows
but one side to the Moon. They move around their common
centre of gravity like a huge dumb-bell with an invisible
handle. The Earth's oceans have partly frozen, and partly
soaked into the cold interior. And its atmosphere has congealed
into a solid snow-like substance. Like its Moon, it is a dead
world, waiting for the inevitable crash that is to bring it back
to some other form of life and usefulness.
ORBITS VARY
It may be as well to mention here that the Earth's orbit is
not always the shape it is now. Sometimes it is almost circu-
lar, while at other periods its ellipticity is so great as to make
the Earth's distance from the Sun vary 14,000,000 miles, instead
of 3,000,000 miles as at present. This change (combined with
the Precession of the Equinoxes, and various geographical
changes) produces considerable variations in the Earth's climate
at long-distant periods.
If we regard the Solar System as a machine, we shall see
that one of its eccentrics takes 109,000 years to go once around.
Yet there are people on Planet Number Three who think that
the whole Universe, stars and all, was made and wound up
6,000 years ago, and that in another thousand years the entire
machine will have run down and worn out !
ORBITS ARE TILTED
Before quitting my illustration of a floating Solar System it
may be as well to say that, besides being unreal (a mere detail)
10
146 HOW TO KNOW THE STARRY HEAVENS
it is faulty, even for an illustration, in one rather important
particular. I have imagined the various planets to be floating
on the surface of water. Now the fact is that the plane, or level,
or surface, on which one planet moves, is not exactly the plane or
surface on which the others move, so that, if the Earth be re-
garded as floating evenly on this ecliptic plane, each of the
other planets will be found to rise a little above its surface at
one part of its orbit, and to sink a little below it at another.
This is the reason why there is not an eclipse of the Sun
every new-moon, and an eclipse of the Moon every full-moon.
It is only at the two nodes, where the plane of the Moon's
orbit crosses the plane of the Earth's orbit, that eclipses can
occur. For elsewhere the Moon passes below or above the
straight line connecting the Earth and Sun. The same is true
of the " transits " and " occupations " of the planets in front
of, or behind, the disc of the Sun.
SAME POLE-STARS EVERY 26,000 YEARS
Now suppose that the first time we visited the Solar System
we took a complete set of photographs of the stars as seen from
Planet Number Three. And suppose that on each of our sub-
sequent visits we take a fresh set of photographs. On compar-
ing these we shall find that the stars themselves are about the
same, but that what should be called (but are not) their celes-
tial " latitudes and longitudes " are changing all the time. This
is of course due to the fact that the North and South Poles are
all the time slowly circling around the poles of the Ecliptic. 1
But if we make many visits with the same interval between
them, we shall find every fourth set practically the same. Thus
the first and fifth sets will be nearly alike, and so will be the
second and sixth, the third and seventh, and the fourth and
eighth. The reason for this is obvious, for when the poles
have " wabbled " around a complete revolution they come back
to the same place on the " star-sphere," and the twelve monthly
1 See North Polar Star Chart.
A REELING WORLD 147
" mansions of the Sun " again coincide with the same constella-
tions of the Zodiac.
STARS ARE DRIFTING
But if we make a closer examination of our different sets of
star-maps we shall find that the stars themselves are slowly
moving about in space. One group of stars is drifting in this
direction, and another in that. Some are coming nearer to us,
and others are receding. Even in a group of drifting stars the
individuals are moving slowly around among themselves, like
the motes in a sunbeam. This slow drift will eventually make
the heavens unrecognisable.
THE GREAT PYRAMID
It is interesting to know that when the Great Pyramid of
Egypt was constructed, the North Pole of the Earth was nearly
as represented in our third return to the planet. The building
was "oriented " (that is, adjusted to the points of the compass)
by making a descending passage, down which the pole-star of
the period (Alpha Draconis, also known as Thuban) shone at
its lowest meridian passage. A temporary pool of water was
formed some distance down the passage, and the image of the
star reflected up a second (but ascending) passage. The result
was that the Pyramid was better oriented than any other build-
ing put up before the invention of the telescope. This peculi-
arity fixes the date at which the Pyramid was built at 3,400
B. c., the December Sun being then in the constellation of
Aquarius (Number 11 in Figure 77).
The long, narrow, but lofty gallery which formed a continua-
tion of the ascending passage was the most perfect transit
instrument ever made, leaving out those provided with magnify-
ing instruments. The large square platform at the top, probably
provided with corner-posts and observing-stations, was also an
excellent arrangement for the study of the heavenly bodies.
By the long-continued use of this truncated pyramid the science
148 HOW TO KNOW THE STARRY HEAVENS
of astronomy might have been largely developed. But unfor-
tunately it was covered up for a tomb as soon as its childish
astrological purpose had been served.
THE FIRST POINT OF ARIES
In this chapter I have kept track of the planetary motions
by referring to the constellation which the Sun appears to
occupy in December. In practice it is found more convenient
to note what stars are beyond the Sun at the Spring Equinox.
Four thousand years ago the March Sun was in the constel-
lation of Taurus (the Bull). The Apis worship of Egypt was
probably founded on this fact. In Europe it was handed down
from father to son by such poetical expressions as " the White
Bull opens the year with his golden horns." Two thousand
years later, when the same equinox had moved back to the
constellation of Aries (the Earn), Jupiter Ammon was repre-
sented with a ram's horns. At present the spring equinox is in
the constellation of Pisces (the Fishes), and is moving in the
direction of Aquarius (the Water-Carrier).
When this slow-moving point was on the margin between
Aries and Pisces, it acquired the name of " the First Point of
Aries," and it still retains this now misleading name.
It may perhaps prevent a misunderstanding if we regard the
Sun (when viewed from the earth) as advancing from right to
left into a fresh " house " every month, while the solar houses
themselves are hooked on to the equinoxes and solstices, and
therefore drift backward at an extremely slow rate. As the
constellations of stars do not share in this backward drift, the
effect is as though the celestial bull, ram, fishes, etc., were drift-
ing forward from one house to another, entering a fresh " house "
every 2,155 years. Or we may imagine that there are twelve
picture frames fastened on to the Ecliptic, and that the Sun
goes from one frame to another in a month, going from right to
left. It will thus occupy one frame every January, the next
one, to the left, every February, etc. In this case the stars
A REELING WORLD 149
form the framed pictures, and they very slowly drift in the
same direction, staying in each frame a little more than 2,000
years.
DECLINATION AND RIGHT ASCENSION
In mapping out the heavens it has been found convenient to
divide them into 360 " longitudinal " degrees (or into 24 hours),
by imaginary lines passing through the Celestial Equator to the
poles. The zero of these divisions crosses the Equator and
Ecliptic where they cross each other at the so-called First
Point of Aries. The same number of " latitudinal " degrees are
used to denote the distance of any celestial object north or
south of the Celestial Equator. These celestial circles are
identical with the terrestrial longitudes and latitudes which are
used to denote the position of any place on our Earth. For
convenience, the earthly longitudes have their zero at Green-
wich, England.
For the sake of simplicity, let us suppose, for a time, that we
are living at Greenwich. We shall find that, owing to the
daily rotation of the Earth, the First Point of Aries appears to
cross the local meridian every twenty-three hours and fifty-six
minutes. At the moment of crossing, the two longitudinal
zeros coincide, and all the stars which are on the local (Green-
wich) meridian at that instant might be said to have a longi-
tude of 0, or of hours. To prevent confusion, however, they
are said to have a Right Ascension of 0, or of hours.
The number of hours and minutes which elapse before a
certain star passes the same (Greenwich) meridian is termed
the right ascension of that particular star. For example, a star
which is on the meridian of Greenwich six hours later than the
Equinoctial Colure which contains the First Point of Aries is
said to have a right ascension of 6 hours, or of 90.
The number of degrees separating a star, etc., from the celestial
equator might be known as its latitude, but for convenience it is
really known as its North (or South) Declination. For exam-
ple, if it is 20 south of the Celestial Equator, it is said to have
a south declination of 20.
150 HOW TO KNOW THE STARRY HEAVENS
By measuring the position of a star or other object in these
two ways, its position in the heavens can be registered with an
accuracy which is limited only by the imperfections of the
observers and their instruments. 1
CELESTIAL LATITUDES AND LONGITUDES
It will be noticed that both of these celestial measurements
start from zeros which move around with the Precession of the
Equinoxes. The result is that both the declination and right
ascension of every star change very slowly as the Earth's axis
reels round the poles of the ecliptic. To avoid this objection,
it would be necessary to use latitudes and longitudes based on
the ecliptic and its poles. For most purposes, however, the
equatorial and polar measurements are most convenient.
IMPROVED EQUATORIAL INSTRUMENT
At the close of the First Chapter I described a very primi-
tive form of equatorial instrument which could be used to
" place " the various heavenly bodies, and to follow their motions,
both real and apparent (see Figure 6).
This instrument can be greatly improved, so far as right
ascension is concerned, by fixing a cog-wheel with 24 teeth at
one end of the polar axis, and placing a spring so that it presses
against one of the teeth. On turning the telescope or pointer
around toward the east, the spring will click off the hours of
right ascension. When the pointer is directed to Alpheratz,
the upper left-hand star in the Square of Pegasus, or at the
most westerly star in the W of Cassiopeia, it is at the zero of
right ascension, which passes through the First Point of Aries.
One click will bring it to the right ascension of Mirach, in
1 When the observer does not live at Greenwich, he has to allow, in all his
calculations, for the difference in time and latitude. For, on the one hand, it is
obvious that if the First Point of Aries is on the meridian of Greenwich, it can-
not at the same time be on the meridian of New York or San Francisco. And,
on the other hand, it is also obvious that a star that is on the zenith at Greenwich
is a long way from the zenith of Cape Town,
A REELING WORLD 151
Andromeda. Another click will bring it in a line with Alpha
Arietes, also known as Hamal. Between the fifth and sixth
clicks it will pass Kigel and Betelgeuse. At the tenth click
Kegulus will be in line. Soon after the fourteenth, Arcturus
will line up. Between the eighteenth and nineteenth, Vega
will be passed; and at the twenty-third click the two right-
hand stars of the Square of Pegasus will fall in line. Each
click will of course represent one hour (or 15) of right ascen-
sion (see Star Charts and Keys).
The same instrument can also be greatly improved, so far as
north and south declination is concerned, by fixing a similar
cog-wheel and spring where the telescope or pointer turns on
the polar axis. On turning the telescope or pointer to the
north or south, the spring will click off every 15 degrees. When
it points to Mintaka, the northwestern star in the Belt of Orion,
it will be on the equatorial zero. One click to the north will
bring it to the declination of Aldebaran, in Taurus, and of the
southern stars in the Square of Pegasus. One click to the
south of the equator will almost bring Sirius in line. Three to
the north will give the equatorial distance of Capella and Arided.
Two clicks to the south will bring it to the declination of
Fomalhaut (see Star Charts and Keys).
By having three times as many teeth in the two cog-wheels,
every click will represent 5 degrees, and the positions of the
stars, etc., can be more accurately ascertained. Many modern
telescopes have wheels or circles so finely divided that the
divisions have to be read off with the help of a microscope.
And their polar axis is turned by clockwork, so as to keep up
with the (apparent) diurnal motion of the heavens (see Figures
43, 46, and 79).
The right ascension and north and south declination of
" many ten thousands " of stars are accurately recorded in star
catalogues. By turning the two axes of an equatorial telescope
till the index fingers point to the position of a star as given in
these catalogues, it is at once placed in the centre of the tele-
scope's field of view. This can be done even in the daytime,
152 HOW TO KNOW THE STARRY HEAVENS
and some of the stars and planets can be found and observed
telescopically while the Sun is above the horizon.
MERIDIAN INSTRUMENTS
If the instrument described above is pointed to the zenith
(or point overhead), and the polar axis is then permanently
clamped, the range of the telescope is reduced to a straight
north-and-south line, forming one half of a great circle of the
heavens. It can be pointed to the northern horizon, to the
polar axis of the heavens, to the point overhead, to the southern
horizon, or to any intermediate point. But it cannot be directed
to any part of the heavens either east or west of the local merid-
ian. In order to observe any heavenly body with this crippled
equatorial it is necessary to wait until the apparent diurnal
motion of the heavens brings the object to the meridian. Sup-
posing that we are still at Greenwich, let us wait till the zero
of right ascension passes the field of view, and then turn the
hands of a 24-hour clock till they point to 24 o'clock. The
clock will then register what is known as sidereal time. 1
As the northeast star in the Square of Pegasus is at present
close to that zero, we can start the sidereal clock when that
star crosses the field of view. It will be found that the star
known as Mirach passes at one o'clock (sidereal), Alpha Arietes
at two, Regulus at ten, and Arcturus at fourteen o'clock. These
stars are therefore said to have so many hours of right ascen-
sion, and by measuring the number of degrees they are north or
south of the Equator (90 from each of the Poles) we can ascer-
tain their north or south declination.
These two classes of observation are so important that greater
precision is obtained by using a special instrument, with no
polar axis, but with large and carefully constructed declination
circles. This instrument is called a Meridian Circle (see Fig-
ure 80). It is mounted on a horizontal axis lying east and
west. This axis rests on the top of two massive piers, so that
1 It should be regulated so as to gain four minutes in 24 hours of solar time.
A REELING WORLD
153
the arrangement is similar to that of a cannon mounted on its
carriage.
When this meridian circle is being used as a transit instru-
ment, the exact sidereal time when a celestial body crosses
the centre of the field of
view is observed, and the
star or planet is said to have
a right ascension of that
number of hours, minutes,
and seconds.
When this meridian cir-
cle is used as a mural circle,
to find the distances of
stars, etc., from the Celestial
Poles or Equator, the clock
is disregarded, but their
distances from the local
zenith are carefully read
off on the large declination
circles attached to the axis
of the telescope. As the
distances of the local zenith
from the Celestial Pole and
Equator have been pre-
viously ascertained, the ze-
nith distance of any object
can easily be turned into
either " polar distance " or
declination (north or south),
as may be preferred.
ALT-AZIMUTH TELESCOPE
FIG. 81. ALT-AZIMUTH MOUNTING FOK
SMALL TELESCOPE
One of the screw motions changes the altitude,
and the other, the azimuth or point of the compass.
There is another form of
telescope-mounting known
as the alt-azimuth. As its name implies, this gives two mo-
tions, one around a perpendicular axis, changing the " azimuth "
154 HOW TO KNOW THE STARRY HEAVENS
or point of the compass, and the other around a horizontal axis,
changing the " altitude " (see Figure 81). This form of mount-
ing, though very handy for terrestrial purposes, is inconvenient
for celestial objects, which almost always move at an angle
with the horizon. For any one living at the North or South
Pole, however, it is the best form, as the perpendicular axis
becomes a polar axis, and the instrument is transformed into
an equatorial.
USES OF INSTRUMENTS
It will be seen from the above that both the alt-azimuth and
the equatorial are capable of being directed to any part of the
sky, and can be made to keep a celestial object in view for any
length of time, provided that it is above the horizon. The alt-
azimuth is, however, difficult to use for most" astronomical pur-
poses, as the diurnal motions can be followed only by turning
both axes at the same time. The equatorial form is therefore
commonly used for general observational purposes. The various
attachments used for celestial photography and spectroscopy
are all applied to telescopes so mounted, with a clockwork
movement to the polar axis, to neutralise the apparent motions
due to the Earth's rotation.
The meridian circle, however, moves solely on the local me-
ridian, and no celestial object can be seen through its telescope
except for a few seconds every 24 hours, as it crosses the field
of view from east to west. Of course such a telescope is of no
use for " star-gazing." Its chief purpose is for measuring the
polar distances and] hour angles of the heavenly bodies on the
celestial " sphere."
CHAPTER XIII
KEPLER'S THREE LAWS
" In the phenomena presented to him, man must [have early noticed] two
kinds of relation. Some things show themselves with other things, and some
things follow other things. These two kinds of relation we call relations of co-
existence, and relations of succession or sequence. Since what continues is not so
apt to attract our attention as what changes, it is probable that the first of these
two relations to be noticed is that of succession. . . . Now of the sequences which
we notice in external nature, some are variable, . . . while some are invari-
able. ... As to these invariable sequences, which we properly call con-sequences, we
give a name to the causal connection, between what we apprehend as effect and
what we assume as cause, by calling it a Law of Nature. ... In original meaning
the word law refers to human will, and is the name given to a command or rule
of conduct imposed by a superior upon an inferior, as by a sovereign or State
upon those subject to it. At first the word law doubtless referred only to human
law. But when, later in intellectual development, men came to note invariable
co-existences and sequences in the relations of external things, they were, of the
mental necessity already spoken of, compelled to assume as cause a will superior*
to human will, and, adopting the word they were wont to use for the highest
expression of human will, called them laws of Nature. Whatever we observe as
an invariable relation of things, of which in the last analysis we can only affirm
that ' it is always so/ we call a law of Nature." Henry George.
UNCHANGING LAWS
PEEHAPS the most striking thing in the study of astronomy
is the fact that everywhere there are evidences that the
whole Universe is absolutely ruled by unchanging laws. There
is no such thing as chance. Hesitation and uncertainty are
unknown. Knowing the forces which are at work, the as-
tronomer can calculate with certainty the positions and move-
ments of the other planets in our System for thousands of
years to come. And even beyond our System, at distances
which are too vast for the imagination itself to fathom, he can
156 HOW TO KNOW THE STARRY HEAVENS
follow up the movements of some of the stellar groups and
predict their future positions and relations.
In order to do these things he has to cast aside all ideas of
chance or miracle, and rely entirely on the immutability of the
laws of Nature.
These natural laws must not be confounded with mere
human decrees, which are all more or less arbitrary, change-
able, and local, as well as ineffective. Human laws may to-day
decree that in a certain country one kind of stealing shall be
legal and praiseworthy, while another kind of stealing shall
be criminal and punishable ; and to-morrow the decree may be
reversed, if the rulers think fit. For example, in Old Testa-
ment times it was against the law to charge interest (usury).
At present it is a legal and even respectable custom. Some
day it may again become a crime.
But natural laws exist without any decree being promulgated.
They are not the creation or invention of mind, but the inevi-
table result of mathematical necessity. They rule alike the
entire Universe. All matter is absolutely subject to them,
whether it be dead or living. They are the same to-day as they
were a billion or a trillion years ago, and they will be the same
a billion or a trillion years to come. For example, 2 + 2 = 4,
always and everywhere. Omnipotence itself could not invent
or change this natural law. It would be just as true if nothing
existed.
George N. Lowe says of Natural Law
" The Law no contract knows, no lease
Of being, waning past its prime
She moves but in Eternities ;
Supreme, she hath no need of Time."
Dr. J. W. Draper, in his " Conflict Between Religion and
Science," says :
" Astronomical predictions of all kinds depend on the admission of
this fact that there never has been, and never will be, any interven-
tion in the operation of natural laws. The scientific philosopher
KEPLER'S THREE LAWS 157
affirms that the condition of the [Universe] at any given moment is
the direct result of its condition in the preceding moment, and the
direct cause of its condition in the subsequent moment. Law and
chance are only different names for mechanical necessity."
KEPLER'S LAWS
It was Kepler l who first discovered the music which regu-
lates the whirling of the worlds through space. His explana-
tions of the planetary motions are known as Kepler's Three
Laws. They are as follows:
I. The orbit of every planet is an ellipse, with the Sun in one of
its foci.
II. An imaginary line drawn from the Sun to a planet will sweep
over equal areas in equal times.
III. The squares of the numbers representing the periodic times
of the planets vary as the cubes of the numbers representing their
mean or average distances.
These laws are easily stated, and, to one who understands
the meaning of the terms employed, are not difficult to com-
prehend. To us, indeed, they seem as obvious, natural, and
inevitable as the statement that two and two make four.
Yet it was not always so. For thousands of years intelligent
astronomers, of many nationalities, were seeking diligently for
these three laws, but never found them. After every other
theory, probable and improbable, had failed to explain the
apparent motions of the planets, Kepler found that the move-
ments of Mars could all be accounted for on the theory that
each planet moves in an elliptical orbit around the Sun with
a velocity varying with its distance from that body. Let us
examine his conclusions.
FIRST LAW
" The orbit of every planet is an ellipse, with the Sun in one of the foci."
In order to comprehend this we must clearly understand
what an ellipse really is.
1 Born in 1571 ; died in 1630.
158 HOW TO KNOW THE STARRY HEAVENS
Get a piece of white pasteboard. Stick a pin upright on one
side of it, near the centre. Tie the two ends of a piece of thread
together, so as to make a loop three inches long. Pass one end
of this loop over the pin, and insert the point of a pencil through
the other end of it. Let the pencil-point touch the card, and
move it around the centre-pin so as to make a six-inch circle.
This circle is really an ellipse with no eccentricity.
Now stick two more pins in the pasteboard, one on each side
of the first, so that each is the eighth of an inch from the
centre one. Pass the loop over them all, insert the point of a
pencil as before, and again move it around on the card, keep-
ing the string stretched all the time. The resulting figure
looks like a circle, but it will be found, on measuring it, that
it is a trifle narrower one way than another. And instead of
having one centre, or focus, it has two eccentric foci, each one
being an eighth of an inch away from the centre of the figure.
The apparent circle is really an ellipse of small eccentricity.
By increasing the interval between the two pins, or foci, we
can produce a great variety of ellipses. When the two foci
are two inches apart, the resulting figure, instead of being a
six-inch circle, is an ellipse measuring 4 inches one way, and
3^ inches the other way. As each focus is some distance from
the centre, the figure is termed an ellipse of great eccentricity
(see Figure 82).
We are now in a position to understand Kepler's First Law,
that each planet moves in an ellipse, with the Sun in one of
the foci. 1
SECOND LAW
" An imaginary line drawn from the Sun to a planet will sweep over equal
areas in equal times."
The simplest form in which we can study this law is where
the elliptical orbit has no eccentricity ; that is to say, when
1 In most astronomical calculations, one focus alone is of importance, the
other one being placed on the shelf, along with the so-called " fourth dimension
of space."
FIG. 82. DRAWING AN ELLIPSE
KEPLER'S THREE LAWS 159
the ellipse is a true circle, with the two foci together at the
centre.
An ordinary carriage-wheel with twelve spokes will do to
illustrate this form of ellipse. The spokes of such a wheel
are all of the same length and are the same distance apart.
FIG. 83. AN ELLIPTICAL ORBIT, DIVIDED INTO TWELVE
MONTHLY PARTS
This ellipse is more eccentric than the majority of planetary orbits,
but is less so than the orbits of comets.
The spaces between them are therefore all the same size ; that
is, they all contain the same number of square inches.
If an insect should crawl straight along the tire of this
wheel at a uniform speed, it is obvious that it would always
take the same interval of time to go from one spoke to another,
and an imaginary line between the insect and the centre of the
wheel would always sweep over the same number of square
inches per second.
It is the same in the case of a planet. " An imaginary line
drawn from the Sun to a planet will sweep over equal areas in
160 HOW TO KNOW THE STARRY HEAVENS
equal times." So when this line has swept over one twelfth of
the area of the orbit, one twelfth-part of the planet's revolu-
tionary period has passed away.
When the wheel is not a circular ellipse, but an eccentric
one, the details are rather different, though the law is the same.
In this case the spokes radiate from one of the foci instead of
from the centre (see Figure 83). And if the area (or number
of square inches) between each of the spokes is to remain the
same, it follows that the long spokes must be set closer to-
gether than the short ones.
From this it is evident that if the insect wishes to go from
one spoke to another in the same interval of time, it must
crawl slowly when on that part of the tire where the spokes
are long and close together, and increase its speed as it goes
to where the spokes are short and far apart.
It is the same in the case of a planet. The speed increases
and diminishes according to the planet's distance from the
Sun, so that, in this case too, " an imaginary line drawn from the
Sun to a planet will sweep over equal areas in equal times."
And, as in the case of a circular orbit, when this line (called a
radius vector) has swept over one twelfth of the area of the
orbit, one twelfth-^&rt of the planet's revolutionary period has
passed away.
Figure 83 is an exaggerated view of the Earth's orbit, with
12 "spokes" (or radius vectors) radiating from the Sun, which
occupies one of the foci. The Earth goes from one " spoke "
to another in an average month (about 30J days), and there-
fore travels faster when nearest to the Sun (in perihelion)
than it does six months later, when it is at its greatest distance
from the Sun (in aphelion). 1
1 If any orbit is correctly marked out in pasteboard, and the twelve wedge-
shaped pieces are then cut out, they will all be found to weigh alike, because,
though different in shape, they all have the same size or area.
KEPLER'S THREE LAWS 161
THIRD LAW
" The squares of the numbers representing the periodic times of the planets
vary as the cubes of the numbers representing their mean or average distances."
The law which we have just discussed deals with the vary-
ing velocity of one planet alone. The one we have now come
to compares together the periodic times of different planets,
and shows that they have a definite relation to the distances of
the planets from the Sun. It also enables us to compare the
mean or average velocity of one planet with the mean or
average velocity of any other planet. The periodic time of a
planet is of course the time it takes to go once around the Sun.
In other words, it is the length of the planet's year.
The outer planets have a longer journey to make than the
inner ones. And they move with less rapidity. Consequently
their years or periodic times are considerably longer.
Observation has shown that Jupiter, which is 5.2 times as
far from the Sun as our Earth, takes 11.86 times as long to
complete a revolution. In other words, Jupiter's journey is a
little over 5 times as long as ours, but his year is nearly 12
times as long.
Let us see how Kepler's Third Law fits in with this. If
we square the periodic times, 1 and 11.86, we get (omitting
fractions) the numbers 1 and 140. And if we cube the distances,
1 and 5.2, we get 1 and 140. These results are identical.
In the above example the smaller period and distance are
both represented by unity (1) to save figuring. Here is another
example, given in miles and days. The distances of Mercury
and Venus from the Sun are 46,000,000 and 67,000,000 miles
respectively. When these numbers are cubed, the latter ex-
ceeds the former 6J times. Their periods of revolution are
88 and 225 days, respectively. When these numbers are
squared, the latter exceeds the former 6J times. These results
(like those in the Earth-Jupiter example) are identical, and if
we perform the operation with any two planets we get a similar
11
162 HOW TO KNOW THE STARRY HEAVENS
result. So we find that " the squares of the periodic times are
in the same proportion as the cubes of the distances."
The velocity of a planet is easily computed when we know
the size of its orbit and the length of its year. Jupiter has
5.2 times as far to go as the Earth, so that if he moved with
the same velocity he would complete a revolution in 5.2 of our
years. As his year is 2.28 times as long as that, the average
velocity of the Earth in its orbit is evidently 2.28 times that of
Jupiter. Accordingly we find that while Jupiter travels 486
miles per minute, our Earth travels 1,108 miles in the same
interval of time (486 x 2.28 = 1108). 1
Kepler not only discovered that the planets move in ellipti-
cal orbits (according to the laws which he formulated), but also
convinced himself that their notions were due to mutual
attraction between them and the Sun. Unfortunately he was
not able to demonstrate this. It was, with him, a probable but
unproved theory.
1 It was afterward discovered by Newton that Kepler's Third Law is the
result of the solar attraction alone, so that it is only strictly correct in the case of
planets consisting of single infinitesimal particles. Where the planet is large, its
attraction must be allowed for as well. The correction does not make much
difference in the result, so far as the above examples are concerned, but it enables
us to extend the law to the satellites of planets and to stellar systems. The de-
tails of this correction will be found in most modern text-books.
CHAPTER XIV
GALILEO'S LAWS OF MOTION
" When we find in Nature certain invariable sequences, whose cause of being
transcends the power of the will testified to by our own consciousness ; such, for
instance, as that stones and apples always fall toward the Earth ; that the square
of a hypothenuse is always equal to the sum of the squares of its base and per-
pendicular ; . . . and, so on through the list of invariable sequences that these
will suggest, we say for it is really all that we can say that these sequences
are invariable because they belong to the order or system of Nature ; or, in
short, that they are Laws of Nature. . . .
Why is it that some things always co-exist with other things ? The Moham-
medan will answer : ' It is the will of God.' The man of our western civilisation
will answer : ' It is a law of Nature.' The phrase is different, but the answer
one." Henry George.
ARISTOTLE'S THEORY OF MOTION
FEOM very ancient times men have tried to find the laws
which regulate motion, both on Earth and in the heavens.
Aristotle, the founder of science, gave the following as his view
of the subject :
"All simple motion must be rectilinear or circular, either to a
centre or from* a centre, each of which is rectilinear, or about a centre.
It is natural for two of the elements earth and water to tend to
a centre ; two air and fire which are light, to tend/rom a centre.
As the motion of all terrestrial elements is therefore rectilinear, it
seems reasonable that the celestial bodies, which are of a different
nature, should have the only other simple motion possible, namely,
circular motion."
This reasoning sounds strange to-day, though it held its own
until the time of Kepler. That philosopher finally threw aside
the celestial part of it, and substituted his laws of planetary
motion, dealt with in the preceding chapter.
164 HOW TO KNOW THE STARRY HEAVENS
GALILEO'S LAWS
The terrestrial part of Aristotle's law also had to give way
about the same time. Galileo l discovered that on our Earth all
bodies move, or abstain from moving, according to the follow-
ing laws, which were put in their present shape by Sir Isaac
Newton.
I. Every body continues in its state of rest, or of uniform
motion in a straight line, unless it is compelled to change that
state by forces impressed thereon.
II. The alteration of motion is ever proportional to the
motive force impressed, and is made in the direction of the
straight line in which that force is impressed.
III. To every action there is always opposed an equal re-
action, or the mutual actions of two bodies are always equal
and directed to contrary parts.
FIRST AND SECOND LAWS OF MOTION
One result of the first law of motion is that a body which is
at rest will stay where it is until it is acted upon by some
force. This is obvious enough, but there is another result
which does not seem so clear. It is that if a body be once set
in motion with a certain velocity it will (if not acted on by any
other force) continue to move for ever in a straight line and at
the same velocity. This tendency to resist change (either of
rest or motion) is known as inertia.
We have no means of testing this first law by itself, for when
we examine an object which appears to be at rest we find that
the attraction of the Earth is holding it in its place ; and when
we set anything in motion we are unable to prevent other forces
from acting on it. If we fire a bullet out of a gun, it is acted
on not only by the initial impulse of the exploding powder
behind it, but also by the continuous attraction of the Earth
beneath it. It has also to contend with the continuous resist-
ance of the air in front of it. If any wind is blowing, it may
l Born in 1564; died in 1642.
GALILEO'S LAWS OF MOTION 165
be affected by a lateral force as well. All of these modify and
finally overcome what (according to this law) would otherwise
have been a uniform motion in a straight line.
But, according to the second law of motion, any secondary
force impressed on the flying object produces a change of mo-
tion proportional to its own strength. So that, if we can ascer-
tain how much this second force has drawn the bullet from its
path, we can find where it would have gone if the second force
had not acted on it.
It has been found by experiment that if a bullet (or any
other object heavy enough practically to neutralise the resist-
ance of the atmosphere) is dropped from a height, the attraction
of the Earth will cause it to fall 16 feet in a second of time.
And we have seen that this force acts on the bullet even when
in motion.
Let us, then, select a perfectly level piece of ground (which
does not share in the convexity of the Earth's surface), and fire
a gun horizontally at a height of 16 feet above the ground.
We shall find that the bullet (instead of keeping on in a
straight line parallel with the ground) will bend down so as to
strike the ground in exactly one second of time. If the act of
firing the gun is made to release another bullet at the same in-
stant and from the same elevation, both bullets will reach the
ground at the same instant, one of them some distance away,
and the other beneath the gun. So far as regards the time in
which the first-mentioned bullet reaches the ground, it will
make no difference whether the charge of powder used is large
or small, though of course a large charge will make the bullet
strike farther away than it would with a small charge.
Now if we could have prevented the attraction of the Earth
from pulling the flying bullet 16 feet out of its course, it would
have kept in a straight line at the same distance from the
ground.
Thus we see that although the first law of motion cannot be
experimentally proved by itself, it can readily be tested in con-
junction with the second law. The only difficulty in the ex-
166 HOW TO KNOW THE STARRY HEAVENS
periment is to make a correct allowance for the atmospheric
friction. To get the most accurate results, the experiment
should be performed in a vacuum, but this is easier said than
done.
THIRD LAW OF MOTION
The Third Law, concerning reaction, is true of both attrac-
tion and repulsion. It is not only true that a magnet will
draw a piece of iron to it, but it is also true that a piece of
iron will draw a magnet to it. When a gun is fired, the back-
ward kick of the gun is equal to the forward impulse of the
bullet, and if the gun and bullet were of the same weight they
would both go the same distance, but in opposite directions.
If two bullets are connected by a string, and then swung
into the air, they will circle around each other as they fly. If
both are of the same weight, they will swing around the centre
of the string. If one is heavier than the other, then the lighter
one will make the larger circles. In the latter case the influ-
ence of the small bullet will be exerted on a greater mass, and
will consequently draw it less out of its course. But neverthe-
less it is obvious that, as in the case of the bullet fired from a
gun, the action and reaction will be equal. 1
It is rather singular that Galileo, while discovering and
fighting for his laws of motion, entirely ignored Kepler's dis-
covery of the three laws of planetary motion, dealt with in the
preceding chapter. This has been charitably attributed, not
to vulgar jealousy, but to " a certain unconscious intellectual
egotism, not always unknown to the greatest minds." Ency.
Brit. art. " Galileo."
1 If anyone still finds these laws of motion hard to understand, he may find
his difficulties melt away as he reads them in the simple form in which they were
first given to an admiring world. They were published as follows :
I. Corpus omne perseverare in statu quo quiescendi vel movendi uniformiter
in directum, nisi quatenus illud a viribus impressis cogitur statum suum mutare.
II. Mutationem motus proportionalem esse vi motrici impress, et fiere sectm-
dum lineam rectam qua vis ilia imprimitur.
III. Actioni contrariam semper et aequalem esse reactionem ; sive corporum.
duorum actiones in se mutuo semper esse aequales et in partes contrarias dirigi.
CHAPTER XV
NEWTON'S LAW OF GRAVITATION
" The force of gravitation acts on every particle of matter, and hence it is not
confined to our own World. By its action the heavenly bodies are bound to one
another, and thus kept in their orbits. It may help us to conceive how the Earth
is supported, if we imagine the Sun letting down a huge cable, and every star in
the heavens a tiny thread, to hold our globe in its place. ... So we are bound
to them, and they to us. Thus the worlds throughout space are linked together
by these cords of mutual attraction, which, interweaving in every direction, make
the Universe a unit." J. Dorman Steele.
THE LAW AND ITS PROOF
THE three laws of motion discussed in the preceding chapter
were at first confined to sublunary dynamics. But Sir
Isaac Newton 1 showed that the heavenly bodies also are subject
to them. He theorised, and after many years of labour proved,
that while they were the cause of the peculiarities described in
Kepler's Laws, they were themselves the result of a general
principle known as the Law of Gravitation.
According to this universal law
" All bodies in the material Universe gravitate toward each other
with a force which is directly proportional to their masses, and inversely
proportional to the squares of their distances from one another."
Perhaps the simplest form in which this law can be correctly
stated is that " every particle of matter in the Universe pulls
every other particle toward it with a force which decreases as
the square of the distance increases."
When the law of gravitation was first brought forward in a
theoretical manner, it seemed to be very feasible, but, at the
same time, to be incapable of proof. The assumption that the
1 Born in 1642; died in 1727.
168 HOW TO KNOW THE STARRY HEAVENS
attracting force varies directly in proportion to the masses
hardly required any proof ; it simply meant that a body com-
posed of three atoms would attract three times as strongly as a
body composed of one atom. It could no more be questioned
than the statement that three equal masses of iron will, under
similar conditions, weigh three times as much as one such mass
alone. But the assumption that the attraction of one body for
another varies in the inverse proportion to the square of the
distance separating them was neither obvious nor easily proved.
There was this to be said in favour of the proposition, however,
that light, heat, and similar forces vary in intensity according
to this rule. For example, if a small lamp shines through a
square twelve-inch hole in a screen one yard away, so as to
light up part of another screen two yards from the lamp, it will
be found that the area illuminated on the second screen contains
four square feet. It is therefore four times as large as the hole
in the first one, and the intensity of the light is obviously
reduced to one quarter of what it was at half the distance. If
the second screen be moved to a distance of three yards from
the lamp, it will be found that the area illuminated measures
nine square feet. It is therefore nine times as large as the hole
in the first screen, and the intensity is evidently only one ninth
of what it was at one third the distance. The rule holds good
for any distance, provided that none of the light is absorbed by
fog, etc.
Newton theorised that the attraction of all the atoms com-
posing the Earth would act as though the pull came from the
centre of the Earth. Now this attraction is strong enough to
cause a body on the surface (about 4,000 miles from the centre of
attraction) to fall 16 feet in one second of time. If this law
of gravitation is true, then an object twice as far from the centre
of the Earth should drop only one quarter as far in the same
interval of time, an object three times as far from the centre
should fall only one ninth as far in a second, and so on for all
distances.
Newton could easily have proved or disproved this theory if
FIG. 84. MOUNT LOWE OBSERVATORY, IN SOUTHERN CALIFORNIA
NEWTON'S LAW OF GRAVITATION 169
he could have gone up 4,000 and 8,000 miles to see how far the
Earth's attraction would cause a body at those distances to fall
in a second. But unfortunately he was not able to do this.
Finally he found a way to get over the difficulty by taking
advantage of the presumed fact that our Moon is kept in her
orbit by the attraction of the Earth. It has been already shown
that on the Earth's surface a bullet fired horizontally from a gun
is, in one second, pulled 16 feet out of its direct course by the
attraction of the Earth beneath. That is to say, it falls just as
fast when it is flying through the air as when it is simply
dropped from the hand. Now the Moon is 60 times as far from
the centre of the Earth as we are. Let us look on it as a big
bullet fired horizontally at that height. We shall then see that
the Earth's attraction is pulling it out of the straight course
it would follow if suddenly left to itself. The theory is that
the Earth's attraction decreases as the square of the distance
increases. The square of 60 is 3,600, so that the Moon should,
in one second of time, be pulled out of its straight course the
3,600th part of 16 feet. This is about one twentieth part of an
inch, and it fits in exactly with the observed motion of the
Moon in its orbit. The theory is therefore true, so far as the
Earth and Moon are concerned. 1
The law has since been applied to all the planets revolving
around our Sun. The satellites of Jupiter, etc., are found to
1 Although this law of gravitation was unknown before Newton, its existence
and universality were suspected by Galileo and hinted at in his " Dialogo dei
Massimi Sistemi." In one place he says:
" Le parti della Terra hanno tal propensione al centre di essa, che quando ella
cangiasse luogo, le dette parti, benche lontane dal globo nel tempo delle muta-
tioni di esso, lo seguirebbero per tutto ; esempio di ci6 sia il seguito perpetuo delle
Medicee, ancorche separate continuamente da Giove. L'istesso si deve dire della
Luna, obligata a seguir la Terra."
Rather freely translated, this reads :
" The different parts of the Earth have such a propensity toward its centre
that, though it should change its place, the said parts, although far from the globe
in the time of its change, would follow it everywhere. An example of this is the
perpetual following of the satellites of Jupiter, although always separate from the
planet. There is a similar instance in the case of the Moon, obliged to follow
the Earth." '
170 HOW TO KNOW THE STARRY HEAVENS
conform to it, and the cometary messengers of heaven are bound
by it. Even the starry systems appear to circle in complete
bondage to this universal law of gravitation.
PLANETS SECURELY TETHERED
We now come to two questions which often puzzle those who
have not made a study of the subject. Why does not a planet,
when it reaches its perihelion, continue to approach the Sun in
a closing spiral till it finally falls into it ? And why does it
not, when at its aphelion, continue to recede in an opening
spiral, and finally go off into the outer darkness of space ? So far
as the principles involved are concerned) these questions are not
difficult to answer satisfactorily. But mathematics are neces-
sary if we wish to go into details and prove every point.
Let us take a single planet moving in a very eccentric orbit.
We will suppose that it has passed its aphelion and is approach-
ing that part of its orbit where it will be nearest to the Sun.
As its distance decreases, the increasing, attraction of the Sun
(being in the same general direction as that in which the planet
is moving) gradually increases its speed, and therefore straightens
its path. For, the deflection Sunward being so many inches
per minute, if the planet moves faster its course will be straighter. 1
The result is that the planet sweeps by the Sun with a rush
that the increased attraction cannot check. 2
As the planet's distance from the Sun increases, the decreasing
attraction (being almost opposite to the direction in which the
planet is moving) gradually checks its speed. It therefore
bends in toward the Sun and finally begins to approach again.
Where the planet moves in an orbit of small eccentricity, the
1 This is seen on our Earth, where a large charge of powder will send a bullet
swifter and therefore straighter than a small charge. If we could stand on the
summit of a lofty mountain, and fire a cannon horizontally with just sufficient
charge, the projectile would sweep around the Earth, and (possibly) knock in the
breech-plug of the cannon from behind.
2 A similar thing takes place with the pendulum of a clock. The Earth's at-
traction brings it down on one side with a rush that carries it up on the other
side.
I UNlv . votTY
L
NEWTON'S LAW OF GRAVITATION 171
above phenomena are not so marked, but the principle .is
the same. In the absence of a resisting medium there is not
the slightest possibility of a planet getting into a closing spiral.
And an opening one is only possible where tidal influences are
very strong. So we need not be afraid of either falling into the
Sun or of breaking loose and drifting into the outer darkness.
These are only possibilities of the remote future, long after the
human race shall have passed away from other causes.
Where a number of planets are revolving around the same
sun, at different distances, their mutual attractions slightly
interfere with their orbits, producing certain periodical jper^wr-
JataVws. It was the study of some of these irregularities which
led to the discovery of the planet Neptune, 1,000,000,000 miles
beyond Uranus, which had previously been regarded as the out-
side planet of our system.
WHAT IS GRAVITATION?
It appears certain that all matter is under the absolute con-
trol of the attraction of gravitation. Atoms and suns are alike
ruled by this law. Every motion is regulated by it, every non-
motion is the result of it.
Although gravitation is now thoroughly understood, both as
to its mode of action and the measure of its power, there is yet
some uncertainty as to its nature. It is generally regarded as a
universal property inherent in matter itself, but some think that
it may be an independent energy controlling matter from the
outside.
The original idea was that gravitation reaches out from one
particle to another, even when they are separated by great dis-
tances, with nothing to connect them, in fact that there is
action at a distance without a medium. This idea has had to
be abandoned, for it is evident that a thing cannot act where it
is not present. So a connecting ether has been " invented " to
carry the energy of gravitation (and what is known as radiant
energy) across from one particle of matter to another. Whether
172 HOW TO KNOW THE STARRY HEAVENS
this ether really exists, what it is like, and how it acts, are
questions that still keep scientists busy, and will probably not
be settled for some time to come.
EFFECTS OF GRAVITATION
Whatever it is, the action of gravitation is always mutual,
and appears to be instantaneous. It operates at all distances
and through all substances.
Its tendency, suddenly applied to scattered bodies previously
at rest, would be to bring together all the suns and worlds of
which the Universe is composed. But, if applied to bodies al-
ready in motion, its effect would be to change direct motions
into curved orbits like those of the planets.
Its effect on any isolated body (like the Sun, or our Earth)
is to cause its particles to arrange themselves in the form of a
sphere, more or less flattened when there is any considerable
rotation. In this sphere the densest forms of matter naturally
gravitate toward the centre, and, while "the globe possesses any
considerable amount of internal heat, there may be an outer
layer of liquid, with expansive gases outside of all.
On the surface of such isolated bodies its effects are almost
inappreciable, the only noticeable effect being that every par-
ticle of matter clings to the planet with an intensity varying
directly with the mass of the planet, and inversely with the
square of the distance between the body and the centre of the
planet. On the same globe all things on the surface are at prac-
tically the same distance from the centre. Therefore they are all,
whether heavy or light, attracted with the same intensity, and
(in a vacuum) fall with the same velocity. The weight of an
object equals its mass multiplied by the force of gravity. If it
were removed to a planet where the force of gravity was twice as
great, its weight would be doubled, though its mass would re-
main the same.
FIG. 85. SPIRAL NEBULA IN URSA MAJOR (M 81)
Lick photograph.
NEWTON'S LAW OF GRAVITATION 173
INTENSITY OF GRAVITATION
As regards the strength of the attraction of gravitation, it is
really very small, being more than a million times weaker than
that of magnetism. Two masses, each of 465,000 American
tons, attract each other with a force of one pound when they
are a mile apart. If the distance between them be doubled,
the attraction is reduced to four ounces. If the distance be
reduced to half a mile, it is increased to four pounds. If one
of the masses be doubled in size and weight the attractive force
is doubled, while if both masses be doubled, the attraction is
quadrupled.
OMNIPOTENCE OF GRAVITATION
The above example, taken by itself, might lead one to suppose
that the attraction of gravitation is of very slight importance in
a Universe where the distances separating the suns and worlds
are so vast. But other forces are local, or operate only under
certain conditions, while gravitation appears to be universal and
to act under all conditions. It therefore becomes an all-control-
ling force whose immensity the mind of man cannot realise. It
possesses some of the attributes of Deity, being omnipotent,
omnipresent, and eternal. It controls the infinitely great and
the infinitely small. It regulates the movements of every speck
of dust that dances in a sunbeam, and, at the same time, of
every sun that sweeps through the boundless depths of space.
The following illustration will give some faint idea of the im-
mense power of the attraction of gravitation :
In going around the Sun, the Earth travels about 19 miles in
a second of time. During the same interval the Sun pulls the
Earth toward him about one eighth of an inch. The power
exerted to produce this insignificant change of direction is so
enormous that if the solar gravitation were to be replaced by
steel telegraph wires they would have to be attached to the
entire Sunward side of the Earth, considerably closer together
than the stalks in a flourishing wheat field. If the bond con-
174 HOW TO KNOW THE STARRY HEAVENS
sisted of a single cast-iron rod, it would have to be thicker than
the Earth itself in order to stand the strain. Yet the mutual
attraction of the two bodies keeps them together without any
visible bond.
Professor Duffield says of this law :
" We cannot but regard it as the most important truth in the
whole book of Nature, and its discovery as the most interesting event
in the history of physical science. As there is but one material
Universe, and the law of gravitation solves the enigma of its struc-
ture, no other problem of equal interest and importance can ever
occupy the attention of the student of Nature."
The above quotation, while paying a just tribute to Newton's
discovery, really overrates the scope and importance of the law
of gravitation. As Ernst Haeckel says :
" Newton had the immortal merit of establishing the law of gravi-
tation and embodying it in an indisputable mathematical formula.
Yet this dead mathematical formula, on" which most scientists lay
great stress, as so frequently happens, gives us merely the quantitative
demonstration of the theory ; it gives us no insight whatever into the
qualitative nature of the phenomena. The action at a distance with-
out a medium, which Newton deduced from his law of gravitation,
and which became one of the most serious and most dangerous
dogmas of later physics, does not afford the slightest explanation of the
real causes of attraction ; indeed it long obstructed our way to the
real discovery of them."
The fact is that we are yet groping almost in the dark, and
need a second Newton to tell us why the law of gravitation
acts as he proved it to act.
PRECESSION AND NUTATION
In Chapter XII the slow reeling of the Earth's axis was
described, without any explanation except the remark that it
was allied to the wabbling of a child's spinning-top. As the
phenomenon is one of the results of the law of gravitation, and
NEWTON'S LAW OF GRAVITATION 175
was first explained by Newton, a few words concerning its
cause may not be out of place here. It should be remembered
that the intensity of the Sun's attraction on a planet varies with
the square of the distance. And it should not be forgotten
that it acts independently on each and every individual atom
composing the planet. An atom at the planet's centre is
attracted less than an atom on the surface facing the Sun, and
is attracted more than an atom on the surface away from the
Sun. The difference in intensity produces the same result as
though the nearest atom was attracted, and the farthest atom
was repelled. In a perfectly spherical planet these differences
would neutralise one another, and the effect would be the same
as though all the atoms were at the centre of the planet.
When the planet's equator is bulged out by rotation, the effect
is the same, providing that the equator of the planet coincides
with the plane of its orbit. But when the planet's equator is
tipped up at an angle with the p]ane of the orbit (as is the
case with our Earth), the relative attraction and repulsion, on
the equatorial bulging, tend to reduce the angle at which the
equator is tipped. The rotation of the planet, however, modi-
fies the movement, so that (in summer and winter) an atom
on the surface, at the equator, makes a lower curve and
crosses the ecliptic a trifle behind the place where it would
otherwise have crossed. This of course has the effect of mak-
ing the polar axis reel slowly back, as already described. The
effect is trifling, but cumulative, so that in the course of time
the axis wabbles completely round. In the case of our Earth
the process is greatly helped by the attraction of the Moon, yet
it is so slight that it takes 26,000 years for the poles to make
one wabble. At the equinoxes the action ceases, so that the
circles described by the polar axis have a tremulous or wavy
outline. As the Moon's orbit is a little inclined to the Ecliptic
and has a " precession " of its own, another irregularity is pro-
duced every 19 years. These two irregularities in the Earth's
precession are together known by the name of nutation.
176 HOW TO KNOW THE STARRY HEAVENS
CAUSE OF REPULSION
At first sight, the theory of gravitation does not seem to ex-
plain such phenomena as the solar flames and corona. These,
and especially the latter, are evidently acted upon by a repellent
force of enormous intensity. The explanation seems to be that
radiant light tends to push away any substance that it strikes.
In large bodies this repulsion is very small when compared with
the force of gravitation. But the former acts according to the
surface, and the latter to the mass. As bodies decrease in size,
the repellent force of light decreases by the square, while the
force of gravitation decreases by the cube. On extremely small
particles gravitation is overpowered by a continuous repulsion
two, ten, or twenty times as great, according to their size. They
are therefore driven off like a bullet out of a rifle, only hundreds
of times more rapidly.
Corona. In the case of the corona, the eruptive particles
are so minute that they appear to be driven clear away into
interstellar space. On the way, some of them are intercepted
by the planets. As they are charged with negative electricity,
and the planets are huge "electrical machines," they arrange
themselves according to the lines of force, and produce such
electrical phenomena as the Zodiacal Light, the Gegenschein,
the Aurora Borealis, etc. All the luminous stars send off simi-
lar negatively electrified particles, and when these, in their
travels, come across a large mass of uncompressed matter, they
cause its surface to glow like the rarefied gas in a vacuum tube.
This appears to be the reason why nebulae are luminous, though
cold with the fearful cold of interstellar space.
Solar Flames. In the case of the solar flames, the eruptive
particles are probably larger, and therefore come to a standstill
sooner or later. They are then buoyed up, not by an atmos-
phere, as our clouds are, but by the pressure of light radiating
from below. If they join together to form larger particles, they
fall back to the surface of the Sun, like the raindrops from our
watery clouds.
NEWTON'S LAW OF GRAVITATION 177
A WREATH OF SMOKE
Sometimes, on a quiet evening, just before sundown, when
hardly a breath of air was stirring, I have watched the blue
rings and spirals of tobacco-smoke, slowly curling, twining, and
eddying in the level glints of dying sunshine.
Now if you will imagine that the atoms of carbon in that
wreath of tobacco-smoke are mighty suns in every stage of solar
life, from the spiral nebulae of solar infancy to the dark, cold,
and lifeless wrecks of superannuated suns, then the curling
and eddying smoke will represent the Universe.
For the great telescopes of our observatories show us star-
clusters and nebulae extended through space in gigantic rings,
eddies, and spirals. If we could watch this celestial cloud of
smoke for a few millions of years, it is almost certain that we
should see these curves and spirals change from form to form
like wreaths of smoke. Through all eternity the star-dust of
which the Universe is composed is eddying and circling through
space that has no limits.
And the very same laws which regulate the curling of the blue
tobacco-smoke regulate the eddying and circling of the innu-
merable nebulae, suns, and worlds which compose our mighty
COSMOS.
NOTE. The laws briefly dealt with in the above three chapters are more fully
discussed and illustrated in Sir George Airy's " Popular Astronomy," which was
written for non-mathematical readers; in George C. Comstock's more recent
" Textbook of Astronomy ; " and in many other works.
12
CHAPTER XVI
ANCIENT COSMOGONIES, AND THE NEBULAR
HYPOTHESIS
" In the intellectual infancy of a savage state, Man transfers to Nature his
conceptions of himself, and, considering that everything he does is determined
by his own pleasure, regards all passing events as depending on the arbitrary
volition of a superior but invisible power. . . . After Reason, aided by Experi-
ence, has led him forth from these delusions as respects surrounding things, he
still clings to his original ideas as respects objects far removed. ... But as
reason led him forth from fetishism, so in due time it again leads him forth from
star-worship. . . . Philosophically speaking, he is exchanging, by ascending
degrees, his primitive doctrine of arbitrary volition for the doctrine of law."
Dr. J. W. Draper.
FACTS VERSUS THEORIES
THE human race is not old enough to have watched the
development of suns and worlds to any appreciable
extent. We cannot therefore know for an absolute certainty
that such a process is at work throughout the Universe. Yet
thinking men are naturally led, by their earthly experiences
and celestial observations, to believe in such a development,
and to theorise as to how the Universe has reached its present
condition. They have even gone beyond the present, and
speculated as to the changes which it will undergo in the
future.
Even a false theory has its value as a stepping-stone to lead
to a true one. It is well, therefore, to theorise even where we
have no direct method of proving the truth or falsity of our
speculations. When a theory gives a reasonable explanation of
observed phenomena, it must have some truth in it. And
when it not only explains all known phenomena, but also
enables us to discover and explain fresh ones, we may regard it
COSMOGONIES, AND NEBULAR HYPOTHESIS 179
as a valuable help for the upbuilding of the Temple of
Knowledge.
Still it is well for us to remember that an unproved theory
is not necessarily a permanent part of that Temple of Knowl-
edge. It may be only a piece of scaffolding that will have to
come down when the building is further advanced.
One of the great troubles in the past has been the tendency
to mistake unproved theories for known facts, and to stretch,
twist, or ignore all facts which refuse to fit in with them.
This is evidently a serious mistake. As Sir William Crookes
said at Berlin, a short time ago :
" It must never be forgotten that theories are only useful as long as
they admit of the harmonious correlation of facts into a reasonable
system. Directly a fact refuses to be pigeon-holed, and will not be
explained on theoretic grounds, the theory must go, or it must be
revised to admit the new fact."
With this necessary warning I will now proceed to outline
a few of the theories which have been held with regard to the
past, present, and future history of the Universe.
HISTORICAL SPECULATIONS
There are in existence several different classes of what pro-
fess to be histories of the Universe in general and of our World
in particular. Some of them have come down to us from pre-
historic times, while others are quite modern. They differ so
much from one another that it is evident they cannot all be
historical. If one is true, the others must be more or less
fictitious.
Some of the more ancient of the " historians " professed to
start from the very beginning of things, although they found it
a difficult thing to do. They began either with a primeval
Chaos that always existed, or with a world-egg that no hen
ever laid. Out of one of these they evolved the Earth and
all that is therein, along with such trifles as the Sun, Moon,
planets, and stars.
180 HOW TO KNOW THE STARRY HEAVENS
The more modern ones do not profess to know of any original
Chaos, and they doubt the veracity of the primitive-egg story.
They modestly content themselves with stating what they be-
lieve to have been the course of events since a certain time,
beyond which they admit that they have no direct knowledge.
And as far as possible they adopt those theories which appear
to be supported by evidence, and to be in harmony with the
laws of Nature as we know them here and now.
These different "histories" may be more or less definitely
divided into the following four classses.
I. Primitive Creationism.
II. Pseudo Creationism.
III. Evolutionary Creationism.
IV. Modern Evolutionism.
I must here content myself with giving a very brief sketch
of the leading varieties of these classes, beginning with the
various forms of Creationism, which I have divided into Primary,
Secondary, and Tertiary.
I. PRIMITIVE CREATIONISM (PRIMARY STAGE)
In early times, when unenlightened men first began to
speculate as to the origin and history of the World and its
surroundings, they found no one to tell them where the Earth
had come from or how it had come into being.
The wise men of each tribe naturally had to answer many
inquiries on the subject. If they had frankly admitted that
they did not know the origin and destiny of all things, they
would have lost their reputation for wisdom. So it was abso-
lutely necessary for them to invent some story which, if it did
not satisfy the mind of a child, would at least put a stop to its
questions. This is probably the way in which all creation
stories have originated, fresh details being gradually, and often
unconsciously, added by successive generations.
From their own limited observations and experiences, these
primitive men naturally inferred that the World could not
always have existed as they found it. They concluded that it
COSMOGONIES, AND NEBULAR HYPOTHESIS 181
must some time, some where, and in some manner have
been either hatched or born. The only other explanation they
could think of was that it might have been made by the Father
of the Gods, for his own amusement.
As a rule the ancients were entirely ignorant of all except
their immediate surroundings. This ignorance compelled them
to view all things from a flat-world standpoint, which natu-
rally and necessarily decided the character of their specula-
tions on the origin of things in general. Having no one to
tell them the facts of the case, they gradually evolved from
their own inner consciousness a number of mythical his-
tories whose ephemeral nature fitted in with their insignificant
Cosmos.
The best known of these, so far as our part of the World
is concerned, is an old Semitic legend, the modern form of
which has been poetically narrated by Milton in his "Paradise
Lost."
According to this account the World (including its attendant
Sun, Moon, and stars) is a manufactured contrivance, invented
and constructed by one who is known as the Architect, or
Creator, of the Universe. Although the account professes to
start from the beginning, it leaves the origin of the Creator
himself in the primeval darkness, and even intimates that he
had no origin, but always existed.
This Architect of the Universe is said to have " created " the
World and its appurtenances. This prodigious work having
been accomplished in six days, the Creator, we are told, " rested
on the seventh day, and was refreshed." He now keeps it in
existence and repair, and personally superintends everything
that takes place on it.
Owing to the machinations of an ambitious and unscrupu-
lous servant, whom he had himself brought into existence,
things did not run smoothly in the newly created World. Its
history (past, present, and future) embraces six thousand years
of strife and one millennium of peace, corresponding to the six
days of work and one of rest. At the close of the seven thou-
182 HOW TO KNOW THE STARRY HEAVENS
sand years the World and its Sun, Moon, and stars will be
destroyed, and will be succeeded by " a new Heaven and a
new Earth," to endure for ever.
II. PSEUDO CREATIONISM (SECONDARY STAGE)
The above is only one out of a number of primitive creation
stories. In the course of time these childlike " histories "
became looked upon as not only true but also " inspired." It
was actually made a punishable offence to doubt their truth
and inspiration. So, when men came to know something as to
the actual dimensions of the Universe, and the relative im-
portance of the Earth in that Universe, they recognised the
improbable nature of these stories, yet hesitated about rejecting
them as untrue and uninspired. The accounts were therefore
" spiritually interpreted," to fit in with the new order of things.
In some cases considerable ingenuity has been used to accom-
plish this. For example, when Astronomy had to be accepted,
the seven thousand years of strife and- peace were declared to
refer to our World alone. When Geology had to be accepted,
the seven days of creation and rest were " spiritualised " into
meaning seven immense periods of time, long enough for suns
and worlds to develop out of "fire-mist." The inconvenient
fact that the Sun and stars were treated as mere appendages
of the Earth, was explained as a " pious fraud " on the part of
the inspired writer, rendered necessary by the ignorance of his
readers.
Some people still accept these stories as true history. Others
have forced themselves to the curious conclusion that they are
not true historically, but that they are allegories, containing
spiritual truths, perceptible only to those who are spiritually
minded. All intelligent and well-informed people now know
that these accounts are simply primitive speculations about
the unknown past. But many of them refrain from hurting the
feelings of others by openly saying so.
COSMOGONIES, AND NEBULAR HYPOTHESIS 183
in. EVOLUTIONARY CREATIONISM (TERTIARY STAGE)
Among those who have rejected Oreationism in both its
primary and secondary forms, there are many who still adhere
to it in an attenuated tertiary form. For want of time or lack
of inclination to formulate a better and truer theory, they take
it for granted that in a very remote past an Infinite and Eternal
Being created an all-pervading substance, or matter out of
nothing, and endowed it with certain permanent qualities and
energies. He then allowed it to evolve without any further
interference. The resulting physical and chemical movements
of this matter have since produced the Universe as we know it.
Some, however, think that at one stage in each world there
was a second creative act, the introduction of organic life in
its lowest form. From this primitive single-celled organism
all the various forms of animal and vegetable life have since
developed by natural laws.
Another interference with mundane events is believed in by
some, the implanting of an immortal soul in man after his
body had sufficiently developed by the operation of natural
laws. This immortal soul was then left to work out its own
salvation or condemnation, without interference.
This tertiary and evolutionary creationism is upheld, in one
or other of its forms, by a more intelligent class of people than
those who are still in the primary and secondary stages, but it
appears to share with those beliefs the disadvantage of not
being either reasonable or true.
However, the truth itself is so astounding to finite creatures
like us, and long-inherited prejudices are so strong, that the
majority of people are not yet able to grasp or ready to receive
it. In the meantime this evolutionary creation-story serves
very well for a temporary basis on which to build a truer and
more reasonable history of the Universe. It will be thrown
away as soon as it has outgrown its usefulness, and the super-
structure can then be fitted on to the eternal foundation of
actual fact.
184 HOW TO KNOW THE STARRY HEAVENS
THE ORIGINAL NEBULAR THEORY
On the basis of a single creative act, Kant, Laplace, and
Herschel I. founded their celebrated Nebular Theory, which
first attracted notice about the end of the eighteenth century. 1
It is rather remarkable that these three great men arrived at
practically the same conclusions by independent and entirely
different routes.
FIG. 86. ORIGINAL, NKBULA, AFTER ITS ROTATION
HAS PRODUCED A DISC-LIKE FORM
Immanuel Kant 2 was led to it in his youth by abstract
philosophical speculations. He outlined the theory in a work
which was published in 1755, but as it did not excite any
interest, he turned his attention to other speculations.
Pierre Laplace 3 was led to its consideration by mathematical
1 Kepler and Tycho Brahe had previously speculated that the Sun and stars
were condensations from celestial vapours.
2 Born in 1724; died in 1804.
8 Born in 1744; died in 1827.
COSMOGONIES, AND NEBULAR HYPOTHESIS 185
reasoning, in middle age, and published it in a modest footnote
in his " Systeme du Monde," 1796. 1
Sir William Herschel 2 was led to it by his lifelong tele-
scopic observations. He discussed it in his papers to the Koyal
Society.
The assumption was that " in the beginning " an inconceiv-
ably vast and attenuated mass of intensely heated gas was
FIG. 87. NEBULA WITH OUTER RING, LEFT BEHIND BY CON-
TRACTION AND CONSEQUENT QUICKENING OF ROTATION
created and put in motion. This original motion led with-
out any further interference to its gradual condensation into
a number of rotating lens-shaped nebulae of thin gas. One of
these has since shrunk and developed into our Solar System,
others have condensed and developed into the stellar systems
which surround us, and thousands (having for some reason
failed to develop) still exist as glowing gaseous nebulae. They
1 He suggested it cautiously, " avec la defiance que doit inspirer tout ce qui
n'est poiut un resultat de 1'observation ou du calcul."
2 Born in 1738; died in 1822.
186 HOW TO KNOW THE STARRY HEAVENS
all move according to the natural laws originally imparted to
matter by the Creator, and eventually discovered by Kepler,
Galileo, and Newton.
As one of these primary rotating nebulae (subject to the
mutual attraction of its own particles) gradually condenses into
a spheroidal form, it naturally increases in density and speed
Fio. 88. CENTRAL CONDENSATION SURROUNDED BY RINGS
of rotation. Much of its energy is also turned into heat, which
radiates into space.
The tendency of every moving body to continue in a straight
line (First Law of Motion) produces a centrifugal force which
increases with the increasing speed of rotation. At last the
equatorial part of the spheroid breaks away in a ring, which
may continue to rotate around the shrinking central body.
Generally, however, it breaks up into a secondary rotating
spheroid, or planet, which continues to revolve around the
primary one, or sun. Each planet goes through the same
process of condensation, throwing off similar rings, which
COSMOGONIES, AND NEBULAR HYPOTHESIS 187
generally collapse into tributary satellites or moons (see Fig-
ures 86 to 90).
In all these secondary and tertiary bodies the original heat
is gradually dissipated by radiation into outer space. The later
rings are smaller than the earlier ones, and give rise to smaller
planets and moons, which go through the various stages more
rapidly than the larger ones.
In time the formation of rings ceases, but the central spheroid
continues to decrease in size and increase in density. Although
FIG. 89. RINGS COLLAPSING INTO PLANETS, AND CENTRAL
CONDENSATION TURNING TO A LUMINOUS SUN
still gaseous, it has long ceased to be a glowing transparent
nebula, and is a compact bluish-white sun, radiating an im-
mense amount of light and heat into space.
Later on, its colour changes to a yellowish white, and after-
ward to yellow. The radiation of heat into outer space goes
on continuously, so that in time it cools off to a reddish tinge.
The colour deepens to crimson and gradually fades away. The
star liquefies and then becomes solid. The crust no longer
188 HOW TO KNOW THE STARRY HEAVENS
glows with light and heat, so that the star ceases to be visible
from outer space.
Meanwhile the various worlds to which it has given rise
have cooled off, become liquid, crusted over, and finally solid-
ified. Life has made its appearance on their surfaces, developed,
flourished, and died away in the growing cold. They are now
dead worlds revolving about a dying sun.
/x^"- xN\
I . N :.'...*f^WKf w..- . / s
\\:<::r :>'//
:. .?%. .' tr
FIG. 90. SOLAR SYSTEM AS IT is NOW
In the course of millions of years the sun itself cools to its
centre, and shrinks till it is but a shadow of its former self. All
forms of energy die away, the times of rotation of the planets
and moons become equal to their periods of revolution, and the
entire system is dead and cold.
Lord Byron once wrote, of this period :
" I had a dream which was not all a dream.
The bright Sun was extinguished, and the stars
Did wander darkling in the eternal space,
Rayless and pathless, and the icy Earth
Swung blind and blackening in the moonless air."
COSMOGONIES, AND NEBULAR HYPOTHESIS 189
The other nebulae which surrounded it have passed through
the same stages and are also dead. The Universe is one vast
cemetery of dead suns and worlds.
" Time was, time is, and time shall be no more. "
Such is the evolutionary history of our Universe which has
been theoretically built up on the most modern form of Crea-
tionism. It is not all true, yet it probably contains more truth
than any of its predecessors. And it is perhaps about as near
the truth as the majority of us are able to get without being
overwhelmed by the awful realities of eternal time and infinite
space.
Many of those who pursue the truth wherever it may
lead them, regardless of prejudices and consequences, have
changed and enlarged the original Nebular Theory to make
it fit in with the discoveries of the nineteenth century. When
thus changed it is no longer in the third stage of Evolution-
ary Creationism, but rests entirely on the fourth and last basis
of Modern Evolutionism. It will be dealt with in Chapter
XVIII.
CHAPTER XVII
THEOKIES AND DISCOVERIES MODIFYING THE NEBULAR
HYPOTHESIS
" We must bear in mind that scientific hypotheses as to the underlying causes
of phenomena are subject to the law of evolution, and have their birth, maturity,
and decay. Theory necessarily succeeds theory, aud while no hypothesis can be
looked upon as expressing the whole truth, neither is any likely to be destitute
of all truth if it sufficiently reconciles a large number of observed facts.
" The notion that we can reach an absolutely exact and ultimate explanation
of any group of physical effects is a fallacious idea. We must ever be content
with the best attainable sufficient hypothesis that can at any time be framed to
include the whole of the observations under our notice. Hence the question,
' What is electricity ? ' no more admits of a complete and final answer to-day than
does the question, ' What is life? ' Though this idea may seem discouraging, it
does not follow that the trend of scientific thought is not in the right direction.
We are not simply wandering round and round, chasing some illusive will-o'-the-
wisp, in our pursuit after a comprehension of the structure of the Universe.
Each physical hypothesis serves as a lamp to conduct us a certain stage on the
journey. It illuminates a limited portion of the path, throwing a light before and
behind for some distance, but it has to be discarded and exchanged at intervals,
because it has become exhausted and its work is done." Professor J. A. Fleming.
SINCE the original Nebular Theory, outlined at the close of
the preceding chapter, was formulated by Kant and La-
place, great additions have been made to our knowledge of
natural laws. And these additions have led to important
modifications of the theory.
Some of the most important of these modifying discoveries
and theories will now be briefly sketched. The reader is par-
ticularly desired to bear in mind Professor Fleming's words as
given at the head of this chapter.
MATTER AND ETHER
Although it cannot be proved, it is now generally agreed that
substance, or matter, exists in two forms, one of which has
many subdivisions while the other appears to be homogeneous.
MODIFYING THE NEBULAR HYPOTHESIS 191
I. The first and most obvious division contains all forms of
what may be termed ponderable matter, or, for convenience,
simply matter. It includes all kinds of substance which are
obvious to our senses. All solids, liquids, and gases belong to
this division.
This sensible matter is supposed to consist of a variety of
very small but perfectly distinct atoms. Those substances
which are built up entirely of one kind of atom are known as
elements, while those containing two or more kinds of atoms
are known as compounds. It possesses such characteristics
as go by the name of gravity, inertia, molecular heat, and
chemical affinity.
II. The other form of substance may be termed ethereal
matter, though it is commonly known as ether ^ It does not
consist of a variety of atoms, like the ponderable matter just
mentioned. It is practically imponderable and is absolutely
imperceptible to the senses. We have therefore only indirect
proofs of its existence.
According to one of the most modern theories concerning this
ether it is composed of particles which are very much smaller
than atoms and are all exactly alike in every respect. These
are supposed to be so crowded together that they act like one
continuous substance. It has also been likened to an incon-
ceivably thin elastic transparent jelly, filling all space not occu-
pied by ponderable matter. It even fills the spaces between
the atoms of the latter. Its existence appears to be proved by
the action of gravitation across apparently empty spaces, and
also by its wave-like movements, which are recognisable as
radiant energy, in the forms of chemism, 2 light, heat, electricity,
and magnetism.
Although we do not know that the above theory is correct,
we are compelled, by reasoning on observed phenomena, to
believe that, in one or other of its two forms, this indestructible
1 Not the bottled ether of the chemist, but the luminiferous ether of the
astronomer.
2 Producing chemical action. It is also known as actinism.
192 HOW TO KNOW THE STARRY HEAVENS
substance, or matter, fills all the infinity of space, without any
void whatsoever.
ATOMIC THEORY
The science of chemistry deals with ponderable matter only.
It has ascertained by experiment that all the varied substances
known are composed of about 80 " elementary " forms of matter.
These exist either separately, as elements, or combined, in cer-
tain fixed proportions, to form chemical compounds. And it
has explained the observed phenomena of chemical combination
by what is known as the Atomic Theory, formulated by Dalton
in 1808. This theory is that each of the elements is composed
of separate and infinitesimal atoms. These are all supposed to
be exactly the same in size, weight, shape, and properties, but
to be entirely different, in size, weight, shape, and properties,
from the atoms of any other element. These atoms may com-
bine to form molecules, but seem to be incapable of further
analysis.
PERIODIC SYSTEM OF ELEMENTS
Although one element cannot be changed into any other ele-
ment, yet the different elements do not appear to be absolutely
independent of one another. When they are arranged according
to their combining weights, they fall naturally into family
groups, reminding one of the octaves of music, where the eighth
notes are related to one another. It is probable, therefore, that
the elements are not ultimate unchangeable forms of matter,
but that their atoms consist of variously arranged groups of one
primitive form of matter. This, when uncondensed, may possi-
bly form the substance of the luminiferous ether.
THE LAW OF SUBSTANCE
One of the most far-reaching of modern discoveries is that of
the Law of Substance, commonly known as the Law of the
Conservation of Matter and Energy.
Indestructibility of Matter. One half of this law of sub-
FIG. 91. DUMB-BELL NEBULA
Lick photograph.
MODIFYING THE NEBULAR HYPOTHESIS 193
stance was discovered much earlier than the other half, and is
still known as the Law of the Persistence or Indestructibility
of Matter. It was worked out experimentally, with the balance,
in the laboratory of Lavoisier, as early as 1789. This first half
of the law affirms that no substance is ever created or destroyed ;
that the Universe always contains exactly the same quantity of
matter ; and that chemical processes do not increase or decrease
its quantity, but merely change its condition.
The modern science of Chemistry has been largely built on
this half of the law of substance, and it is now accepted by all
thinking men.
Conservation of Energy. The other half of the law of sub-
stance is known as the Law of the Persistence of Force or
Conservation of Energy. It was worked out experimentally, in
the workshop of Eobert Mayer, in 1842. This second half of
the law of substance affirms that no force is ever created or
destroyed ; that the Universe always contains exactly the same
amount of energy ; and that chemical and mechanical changes
do not increase or decrease its amount. They merely change
its condition from potential to actual, or from actual to potential,
leaving the sum total of the two forms of energy eternally the
same.
The physical sciences have been largely built on this half of
the law of substance, and it is now adopted (either as a fact or
as a working hypothesis) by all thinking men.
Actual energy manifests itself in several different ways, and
one kind of it can readily be changed into another. Sound,
heat, light, chemical action, electricity, magnetism, etc., are all
manifestations of energy, and any one of them can be converted
into any other without actual loss of energy.
Some one may here say, " That sounds like perpetual motion,
which we know to be an absurdity."
It is true that perpetual motion is an absurdity so far as
machinery constructed by man is concerned. That, however,
is not because any of the energy is destroyed, but because it is
turned into a form which is not available to us. It still exists,
13
194 HOW TO KNOW THE STARRY HEAVENS
and accurate measurement will show that there is no loss of
energy whatever.
All forms of energy are available to Nature, so that the Uni-
verse as a whole is not only a " perpetual-motion machine," but
is the only one that can possibly exist.
SPECTROSCOPIC DISCOVERIES
The discovery of the dark lines in the solar spectrum, by
Wollaston and Frauiihofer, and their explanation by Kirchhoff
and others, after fifty years of study, have put the atomic theory
on a solid basis, and given an immense help in solving the
riddle of the Universe. KirchhofFs discovery, in fact, deserves
to rank with the discovery of the law of gravitation by Newton.
While the one enables us to weigh the suns and worlds in a
balance, and to find out their past, present, and future move-
ments, the other tells us what they are made of and the
condition they are in. It also enables us to detect celestial
phenomena and movements that the telescope by itself fails
to reveal. These achievements have, however, been already
described in former chapters, so need not be further dwelt on
here.
KINETIC (OR VIBRATORY) THEORY OF SUBSTANCE
It is now concluded that all the different forms of energy
gravitation, sound, heat, light, chemical action, electricity,
and magnetism are only different manifestations of one
primitive force. This is commonly conceived to be a vibratory
motion of the atoms of matter dancing to and fro in empty
space, and influencing one another at a distance without any
medium.
When this theory is examined, however, some parts of it
prove not only mysterious, but improbable, if not impossible.
We can find no satisfactory answer to the question, How can a
thing act where it is not present ?
MODIFYING THE NEBULAR HYPOTHESIS 195
PYKNOTIC (OR CONDENSATION) THEORY OF SUBSTANCE
To overcome this objection it has been suggested that all
space is filled with a simple primitive continuous substance,
which has a tendency to contract or condense around infinitesi-
mal centres. These centres of condensation are the atoms of
ponderable matter, and they are supposed to float in the uncon-
densed matter, which goes by the name of ether. The condensa-
tion of the atoms causes a stretching of the surrounding ether.
The efforts of the atoms to complete their condensation are
therefore opposed by the resistance of the ether to the further
increase of its strain. The result is the accumulation of an
immense amount of potential energy around the atoms, and of
actual energy in the ether. These two forms of energy are
continually varying, but the sum of them is ever the same.
They manifest themselves as light, heat, gravitation, and all the
other modes of motion with which we are acquainted, and
thereby produce all the varied phenomena of Nature.
These two theories of substance are now being tried in the
crucible of experiment and observation. Fresh facts are being
discovered every day, and a satisfactory and comprehensive
theory will probably be constructed before very long.
ELECTRO-MAGNETIC THEORY OF LIGHT
Until 1872, "chemism," light, heat, electricity, and mag-
netism, were almost universally regarded as separate and dis-
tinct entities. We now look upon them as merely sensations
or effects due to one solitary form of radiant energy, which is
given off by all radiant suns, and manifests itself differently
according to the way in which we observe it.
According to Maxwell's electro-magnetic theory of light
(which is now generally accepted), heat, light, magnetism, etc.,
are simply different manifestations of electricity generated and
sent out by the huge electrical machines which we know as
suns or stars. They are, in fact, due to stresses and strains in
the luminiferous ether.
196 HOW TO KNOW THE STARRY HEAVENS
It will be seen that the tendency now is not to seek for
mechanical explanations of electrical phenomena, but to look
for electrical explanations of mechanical phenomena.
ULTRA-ATOMIC (OR ELECTRONIC) THEORY
Kathode Rays. If a wire which carries a current of elec-
tricity be cut in two, and the ends kept apart, the flow is of
course stopped. But if the cut ends (or terminals) are inside
a closed glass vacuum-tube, the current leaps across the almost
empty space, and the tube is filled with a phosphorescent glow.
Sir W. Crook es, and Professor Thomson, after years of experiment
with these vacuum-tubes, concluded that this cold light is due
to a torrent of small negatively electrified particles of radiant
matter, chipped off the " kathode " or negative terminal.
These kathode particles resemble ordinary matter in possess-
ing inertia, and will turn a toy windmill when they strike it.
By allowing some of them to pass through a slit in a mica
diaphragm, and then to skim along the surface of a screen
coated with zinc sulphate, their course becomes visible (in the
dark) to the naked eye. Ordinarily the particles travel in a
straight line, so that their course resembles a straight jet of
steam. But when a magnet (or a plus pole) is brought near,
the jet of luminous particles bends toward it, as a horizontal
jet of water bends toward the earth. The amount of the
deflection depends on the strength of the attracting current,
the mass of the particles, and the speed at which they travel.
It has thus been ascertained that the particles are from 700 to
1000 times less (in mass) than an atom of hydrogen, and that <
they travel at a speed comparable with that of light. The
torrent gives a negative electric charge to any bodies it may
strike, and it appears to be virtually an electric current.
Metals are transparent to it, and even after passing through
them it affects a photographic plate more powerfully than
ordinary light.
Rontgen or X Rays. Any object struck by these kathode
particles gives off what are thought to be invisible ether waves.
FIG. 92. NOVA PERSEI, 1901. SHOWING MOVEMENT OP
SURROUNDING NEBULOSITY
Lick photographs.
(a) Nov. 7-8, 1901. Exposure 7 h. 19 m.
(6) Jan. 31 and Feb. 2, 1902. Exposure 9 h. 45 m.
MODIFYING THE NEBULAR HYPOTHESIS 197
These are commonly known as Rontgen or X Rays. They
radiate from their source in straight lines, and are not deflected
by a magnet or electrical field. They can pass through wood,
metal, leather, and flesh without losing their power of affecting
a photographic plate. They do not impart negative charges to
the bodies on which they fall, but they discharge charged
bodies by making gases better conductors of electricity.
Becquerel Rays (Alpha, Beta, and Gramma). Besides the two
kinds of STIMULATED radio-activity just described, some forms of
matter possess a SPONTANEOUS radio-activity. All compounds
containing the heavy elements known as radium, thorium,
cerium, and (perhaps) actinium, give out, continuously and
spontaneously, three distinct kinds of radiant energy. These
are known as
Alpha, or Atomic Rays.
Beta, or Kathodic Rays, and
Gamma, or Rontgen Rays.
Alpha or Atomic Rays. These are the most noticeable of
the spontaneous radiations, and appear to consist of atomic
projectiles shot out in all directions from the radio-active
substances. They move in a straight line with a velocity of
about 20,000 miles per second. They are not ordinarily drawn
aside by a magnet or by an electrically charged body, but in
a very stroDg electrical field they are deflected toward the
negative pole. The direction and amount of this deflection,
with a current whose intensity is known, prove that they con-
sist of positively electrified atoms whose mass is two or three
times as great as that of hydrogen atoms. 1 On account of their
great size they cannot pass between the atoms of ordinary mat-
ter. They can therefore be stopped by a sheet of paper. They
affect a photographic plate more slowly than the beta particles,
but discharge electrically charged bodies more quickly.
1 They may possibly be atoms of the newly discovered metal helium, whose
atomic weight is four times that of hydrogen. This element is never found except
in company with the heavy radio-active elements we are discussing, and its
spectral line has been found in the gaseous emanations from radium.
198 HOW TO KNOW THE STARRY HEAVENS
Beta or Kathodic Rays. These are identical with the kathode
rays of the Crookes tube. They therefore consist of negatively
electrified particles about 2,000 times smaller (in mass), than
the alpha atoms. They travel in a straight line at about the
speed of light. They can pass through a plate of platinum or
an inch of solid iron, and then strongly affect a photographic
plate. On account of their small size they cannot discharge
electrified bodies so quickly as the more ponderous alpha
projectiles.
Gramma or Rontgen Rays. These are identical with the
x rays of the Crookes tube. They are probably ether-waves
caused by the breaking up of the atoms. They can pass
through six inches of iron and then affect a 'photographic
plate.
Of all the radio-active elements yet discovered, radium is by
far the most active. It is indeed so active that its compounds
are measurably warmer than surrounding objects. In the dark
they give off a faint light like that of a glow-worm. When
they are placed near a screen covered with zinc sulphide, the
impact of the bombarding projectiles on the zinc crystals gives
a display which (seen through a microscope) resembles a sky
full of shooting-stars.
The available evidence seems to show that those elements
whose atoms are very heavy and complex were built up under
conditions very different from the present ones, and are now
very slowly disintegrating, by stages, into lighter and simpler
elements. 1 This would explain the apparently inexhaustible
supply of energy possessed by the radio-active elements.
In this connection Professor R A. Millikan says :
" The disintegration of a gram of uranium, or thorium, or radium,
sets free at least a million times as much energy as that which is
represented in any known chemical change taking place within a
gram weight of any known substance. The experiments of the last
1 This would be analogous to the complex molecules which are built up by
living organisms (at the expense of solar energy) only to disintegrate into simpler
ones at the first available opportunity.
MODIFYING THE NEBULAR HYPOTHESIS 199
eight years have then marked a remarkable advance in science, in
that they have proved the existence of an immense store of sub-atomic
energy." l
Glowing metals and other hot bodies give off radiant matter
somewhat similar to some of the forms described above. Cold
metals do the same when they are exposed to ultra-violet light.
It is possible that all forms of matter may emit similar particles
all the time.
It would be absurd to suppose that these bodies can give out
either radiations or particles continuously without any loss of
energy or weight, but the loss may sometimes be so small that
they may appear to do so. In some cases the radiations may
have been previously received from the Sun, and the vibrations
changed to a rate which our senses or instruments are capable
of perceiving or registering.
The particles of which most radiant matter is composed are
variously known as electrical corpuscles, electrons, ions, or
negative particles. It is worthy of note that different sub-
stances do not give out different kinds of corpuscles, but that
the latter appear to be all alike, whatever their source.
An atom of hydrogen is the smallest of all known atoms. In
decomposing water by electricity, an atom of hydrogen carries
a certain definite and indivisible charge of electricity, which is
known as an electron. Now it has been found that one of our
newly discovered corpuscles [although it is from 700 to 1000
times less (in mass) than an atom of hydrogen] carries the same
amount of electricity. This, however, is always what is known
as a negative charge. Positively charged corpuscles have not
yet been discovered, and they probably do not exist in a free
state.
It is possible that all the various forms of " elementary "
atoms composing ponderable matter are built up of concentric
layers of corpuscles, the layers being alternately positive and
1 "Recent Discoveries in Radiation," Popular Science Monthly, April, 1904.
Perhaps this advance will help to set at rest the long-standing dispute between
the astronomers and the geologists as to the duration of geologic times.
200 HOW TO KNOW THE STARRY HEAVENS
negative. In this case we may assume that the outside layer
is always composed of negative corpuscles, so that the atoms
all attract one another at a distance, but mutually repel when
close together, especially when they are of the same sign. For
otherwise the atoms would mingle and lose their individuality.
If this is so, then the vibrations which produce light, etc., are
not vibrations of the atom itself, but of the electrons or cor-
puscles of which it is composed.
According to this Electronic Theory, electrons or corpuscles
are the ultimate particles of which all kinds of atoms consist.
The atoms themselves are " star-clusters " of electrons in stable
orbital motion at planetary distances from one another. On
this hypothesis a cluster of about 700 electrons forms an atom
of hydrogen. An atom of oxygen contains about 11,200 of
them. An atom of gold contains about 137,200. And so on.
It appears probable that, besides the corpuscles which are
built up into atoms, there are such vast quantities of free nega-
tive corpuscles that they fill all space . to saturation. If so,
then the luminiferous ether itself consists of these electrons or
negative particles. 1
1 This Electronic or Ultra-Atomic Theory appears to have needlessly alarmed
many people, who think that it will lead to the overthrow of the Atomic Theory
and of the Law of Substance. They may perhaps be set at ease by the following
words by Sir Oliver Lodge, F.R.S., at the close of an article on " Radium and its
Lessons." He says:
" Let me conclude by asking readers to give no ear to the absurd claim of
paradoxers and others ignorant of the principles of physics, who, with misplaced
ingenuity, will be sure to urge that the foundations of science are being uprooted,
and long-cherished laws shaken. Nothing of the kind is happening. The new
information now being gained in so many laboratories is supplementary and stim-
ulating, not really revolutionary, nor in the least perturbing to mathematical
physicists, whatever it may be to chemists ; for on the electric theory of matter it
is the kind of thing that ought to occur. And one outstanding difficulty about
this theory, often previously felt and expressed by Professor Larmor, that
matter ought to be radio-active and unstable if the electric theory of its constitu-
tion were true, this theoretical difficulty is being removed in the most brilliant
possible way." Nineteenth Century Magazine, July, 1903,
FIG. 93. SPECTRA OF NOVA PERSEI, SHOWING CHANGES
Yerkes Observatory.
Feb. 27.
Feb. 28.
Mar. 6.
Mar. 15.
r. 28.
MODIFYING THE NEBULAR HYPOTHESIS 201
REPULSION OF LIGHT
It has been discovered, first by theory and afterward by ex-
periment, that when the vibrations of light strike any object
they push against it with a force which varies according to the
square of its diameter. And as the attraction of gravitation,
acting on the same object, varies as the cube of its diameter, it
follows that, if the object is small enough, it will be violently
repelled from the source of light.
These facts form a simple and sufficient explanation of many
physical phenomena, both terrestrial and celestial, and have
been several times alluded to in the preceding chapters.
EVOLUTION OF LIFE, ATOMS, AND WORLDS
About the beginning of the nineteenth century, Goethe,
Lamarck, and some other naturalists rejected the theory of the
special creation of the different species of plants and animals.
They contended that all have developed, by natural means,
from the simplest forms of life, which originally came from
non-living matter. This development, they claimed, was car-
ried on by means of the interaction of heredity and adaptation.
In 1859 Charles Darwin proved the truth of this theory of
descent, as far as such a theory is capable of proof, and showed
that it was caused by a struggle for existence and the resulting
natural selection by the survival of the fittest.
The late Herbert Spencer first recognised that the same law
of evolution dominates the entire Universe. He showed that
its transformations are exhibited, not only by the Universe as
a great whole, but in all its details. They can be traced in the
Solar System, and in the inorganic Earth ; in the organic world
as a whole, and in each individual organism ; in society at
large, and in the individual mind. They are also clearly recog-
nisable in all the products of social activity.
From suns and worlds to molecules and atoms, all things
struggle for existence, and survive or perish according to their
202 HOW TO KNOW THE STARRY HEAVENS
fitness. The reason why atoms and suns are in a state of
stable equilibrium that seems to be the result of mental con-
trivance is that all the forms which do not possess that " fitness
to survive " are promptly changed into forms that are not
mutually interfering. In both atoms and suns there is an
unconscious struggle for existence leading to an equally un-
conscious survival of the fittest.
PRIMEVAL TIDES
The shape, size, condition, and movements of any heavenly
body are due to the forces which act (or have acted) upon the
individual particles of which it consists. The mathematical
study of these forces has led to the discovery that the develop-
ment of suns and worlds is largely controlled by tidal action
while they are still in a gaseous or liquid-gaseous condition.
In a solar system like ours, and in a binary system or star-
cluster, the various bodies are moving with a certain regularity
along practically non-interfering lines. . This is not the result
of skilful manoeuvring by clever world-pilots. There is no one
steering them out of danger. Their apparent security is simply
due to the fact that interfering movements soon lead to catas-
trophes which effectually remove the insecure members of the
family circle, but leave the others alone. It is simply an in-
stance of the struggle for existence and of the survival of the
fittest.
But the sovereign suns which roam at large through space
all appear to be flying at random. So far as we know they
have no regular orbit, but each one is apparently dashing
blindly in the direction of least resistance to the surrounding
centres of attraction. They may be likened to a cloud of
mosquitoes or a vast swarm of bees.
Let us suppose that two gaseous suns are approaching one
another from opposite directions. Each one is sailing majes-
tically along in a practically straight line, and at the same
time is serenely spinning around on its axis.
If there were pilots on board, who could control them by
MODIFYING THE NEBULAR HYPOTHESIS 205
means of a steering-apparatus, they would probably get in a
flurry sometimes, steer wildly, and cause a collision. But as
there is no one in charge to make trouble, an "accident" of
this kind seldom takes place.
It seems natural to suppose that if the two suns do not
actually collide they will pass each other and go on their way
as though they had never met. This is the case, indeed, when
they are a great distance apart. But if they pass very near to
one another the law of gravitation compels them to salute each
other. Their original speed is added to by their mutual attrac-
tion. They swing in toward one another, pass like a flash, and
go off on a curve which soon becomes practically a straight
line.
So far the only effect noticed has been a change of direction.
But there appear to be other changes produced. When the
two bodies were making their bow to each other, the central
particles in each of the suns were attracted less than the
nearest particles, but more than the farthest. The intensity
of the pull varies in the inverse ratio to the square of the dis-
tance (see Chapter XV). The result is the same as though
the nearest and farthest particles in each body were strongly
repelled from one another. The two suns therefore lose their
original orange-shape (due to attraction modified by rotation)
and become more or less the shape of a pear. After they have
passed each other, never to meet again, they continue to rotate
as before, and- the small end of each pear-shaped star swings
around as a mighty tidal wave. The centrifugal tendency is
so strong that the two ends gradually draw the central matter
to them, forming a dumb-bell arrangement which finally breaks
in two. The result is that each star becomes a " binary " or
double star, in which both of the partners rotate in the same
direction as that in which the parent moved. The telescope
and spectroscope show the heavens to be crowded with such
binary systems. In some cases the rotation is so rapid as to
show that the partners are still clinging together like Siamese
Twins.
204 HOW TO KNOW THE STARRY HEAVENS
The binary system known as V Puppis appears to be in this
stage of evolution. The combined mass of the two partners is
equal to that of 66,000 worlds like ours, and they are still in
a distended gaseous state. Yet they are shown to revolve (or
rotate) in the remarkably short period of 35 hours.
The theory of tidal evolution (on which the above descrip-
tion of "puppation" is founded) was demonstrated mathe-
matically by Professor George Darwin from an examination
of the interaction between the tides and the motions of the
Earth and Moon.
I
CHAPTER XVIII
MODIFICATIONS OF THE NEBULAR THEORY
" Worlds on worlds are rolling ever,
From creation to decay,
Like the bubbles on a river,
Sparkling, bursting, borne away." P. B. Shelley.
" Without beginning, aim or end ;
Supreme, incessant, un begot ;
The systems change, but goal is not,
Where the Infinities attend." G. Sterling.
IMMORTALITY OF THE UNIVERSE
THE discoveries and speculations I have just sketched, and
others which have not been mentioned, have led to some
important modifications and developments of the original Neb-
ular Theory.
Among other changes, the foundation of Creationism has
been rejected by the foremost minds, so that the whole theory
is evolutionary. We now recognise no beginning and acknowl-
edge no end. We can conceive of no space which is not occu-
pied by matter in one or other of its two forms. We can admit
of no exhaustion of energy leading to a dead Universe. We
have come to the conclusion that nothing exists apart from
matter and its energies. Mind, in the form of desires and in-
clinations, exists not only throughout the animal and vegetable
kingdoms, but likewise in so-called dead matter. Even the
molecules, atoms, and corpuscles have a kind of sensation and
will.
-FROM DEATH UNTO LIFE"
The secret of the perpetual youth of the Universe appears to
lie in the fact that the millions upon millions of heavenly
206 HOW TO KNOW THE STARRY HEAVENS
bodies do not move in paths of eternal regularity, but that they
interfere with one another. This causes their orbits to be
changeable, and, to some extent, irregular. The result is that
every once in a while two of them come into violent collision,
thus changing a large amount of potential into actual energy.
If two trains travelling at the speed of a mile a minute were
to meet " head on," it is obvious that an enormous amount of
latent energy would be turned to actual energy. If they were
travelling 750 times faster (which is the speed at which our
Sun is going toward Vega), the amount of actual energy pro-
duced by the shock would be 540,000 times greater ( = 750x
750). And if the two trains were to be loaded down till they
each equalled our Sun in weight, the energy produced would
be proportionately increased. It would be equal to that caused
by a direct collision between our Sun and another star of the
same mass and travelling at the same speed;
The result of such a collision could be calculated mathe-
matically, but the most vivid imagination could not picture it.
Yet there are suns many thousands of times larger, travelling
at a speed many times as great, and apparently liable at any
time to come together with a crash, or to glance by one another
with a result almost as disastrous. In the event of such a
collision the temperature of the colliding bodies would be raised
many thousands of degrees. They would expand into a huge
mass of thin gas, which would, in time, cool off to the tempera-
ture of space (probably about 230 F.). That is to say, the
old and feeble perhaps dead suns would spring into new
youth and drift away as a more or less diffuse and shapeless
mass of glowing gas. This would gradually assume the form
of a rotating spiral nebula, and begin once more the great drama
of evolution.
This picture is no freak of the imagination, but appears to be
an illustration of an actual fact. In all probability such things
have always been taking place, are taking place now, and will
be taking place when our Solar System has for ever disappeared
and been forgotten.
MODIFICATIONS OF THE NEBULAR THEORY 207
We thus see that the evolution of suns and worlds does not
necessarily take place once and then cease. It is apparently
repeated over and over again ; here, there, and everywhere. As
Ernst Haeckel says, " while the rotating masses move toward
their destruction and dissolution in one part of space, others
are springing into new life and development in other quarters
of the Universe."
SOME NEBULA ARE COLD
The Nebular Theory of Laplace was that the nebulae were
extremely hot, and rotated in lens-shaped masses which threw
off regular rings. It has since been modified for both theoreti-
cal and observational reasons.
In the first place it is evident that, however hot a thin nebula
may be at its first formation (due to the collision of mighty
suns), there is nothing to prevent that heat from radiating away
into outer space. When it has done so there is no fresh supply
of heat to draw from except that produced by the action of
gravitation drawing its spirals back into condensed centres, and
it takes millions of years for that to produce any great increase
of temperature. So in the meantime it may be invisible except
at the outer surface. There a rain of negatively electrified cor-
puscles (sent out by the myriads of radiant suns) probably
causes it to glow with a cold light akin to many other corpus-
cular radiations. 1
In the second place it has been found that the most common
form of nebula seen in the telescope is not lens-shaped, but
spiral. While some of the nebulae (like the Great Nebula in
Andromeda) seem to be condensing into a vast central globe
surrounded by tolerably even rings, others (like the Spiral
Nebula in Canes Venatici) appear to be condensing around a
number of centres, as though forming a social system or star-
cluster (see Figures 63, 64, and 85).
1 Among these may be mentioned the Solar Corona, the tail of a comet, the
Zodiacal Light, the Gegenschein, the Aurora Borealis and Australis, St. Elmo's
fires, the phosphorescence of fishes and other animals, the kathode rays of our
electricians, etc.
208 HOW TO KNOW THE STARRY HEAVENS
EVOLUTION OF SOLAR SYSTEM
When our Sun was in its first nebular stage (perhaps due to
collision), it was probably a hot and more or less spherical mass
of inconceivably thin gas, immensely larger than the whole Solar
System is now. Its particles would then be so far apart that
the most perfect vacuum we can produce would be dense in
comparison. Seen from a great distance, it would probably re-
semble the symmetrical planetary nebulae which are revealed
by our telescopes (see Figure 99).
Presuming that this planetary nebula was not interfered with
from outside, it would not lose its regularity of form, but would
gradually condense and acquire a spiral structure. But if any
wandering stars had happened to pass through it, it might for a
time have assumed the torn explosive appearance of the great
Trifid Nebula (see Figure 67), and if it had collided with a
neighbouring nebula it might possibly "have acquired an irregu-
lar form like that of the Great Nebula in Orion (see Figure 68),
but of course it would have been on a much smaller scale.
Unless very much scattered, however, the mutual attraction of
its particles would, in the course of time, again bring about a
regularity of form and structure.
When a cricket-ball is struck by a bat, the size, shape, and
density of the two bodies, and their position, speed, and direc-
tion, determine the flight of the ball and the subsequent adven-
tures it may meet with. In the same way the colliding bodies
which we assume to have given birth to the nebulous mass
under consideration must have received a certain moment of
momentum which has produced every peculiarity now possessed
by the Solar System which has developed from it.
After the explosive energy of the original collision had pro-
duced the hypothetical nebula, every gaseous particle in it was
left at a certain temperature and in a certain position. It was
also moving in a certain direction with a certain velocity. The
varied and irregular nature of these movements led to innumer-
able collisions between the particles. Some of the energy pos-
MODIFICATIONS OF THE NEBULAR THEORY 209
sessed by the particles was thus turned to heat, which, like the
original heat of the nebula, radiated away into outer space. The
varied movements of the particles, and the resulting collisions,
naturally ended in the survival of the movements which did not
interfere with one another. The mass therefore gradually at-
tained a rotating disc-like form, lying on a plane and moving
in a direction determined by its original " moment of momen-
tum." In this way every particle moved in the path of least
resistance, and therefore with the least, expenditure of energy.
By this time the temperature of the nebula was very much
reduced by radiation into outer space. It was probably invisi-
ble except near the surface, where the radiant energy from sur-
rounding suns made the light surface-gases glow with a cold
radiance akin to that of the kathode rays of our vacuum tubes.
The dissipation of the original heat by radiation led to the
contraction and condensation of the entire mass. The decrease
in size of course led to an increase of the density and speed of
rotation. As the speed was greatest toward the centre, a rotat-
ing and indrawing spiral was the result (see Figures 63 and 85).
The centre of this spiral became a vast condensation which,
in the case of our System, drew to it the great mass of the neb-
ula. Four important subordinate centres of condensation were
also formed, as well as a great number of lesser ones. These
centres gradually absorbed the nebuldus matter around them,
and thereby increased continuously in density.
At first these centres of condensation did not have any rota-
tion except that due to the spiral indrawing revolution of the
whole mass. That is to say, each subordinate centre rotated at
the same speed that it revolved. But as its particles were drawn
in toward the centre, the rotation grew more rapid, because they
had a shorter journey to go and were nearer the local centre of
attraction. All the subordinate condensations, therefore, ac-
quired an ever-quickening speed of rotation in the same direction
as the revolution of the whole system. In the case of the
central condensation there would be no distinction between
rotation and revolution.
210 HOW TO KNOW THE STARRY HEAVENS
As the particles in one of these condensations gradually fell in
toward its centre, their friction with one another turned a large
part of its energy into heat. So much heat was produced in this
way that it could not all radiate into space. Its temperature,
therefore, rose, slowly but steadily, till it glowed like a little sun.
As a result of the changes outlined in the preceding three
paragraphs, the centres of condensation, though they decreased
in size, continually increased in density, speed (of rotation and
revolution), and heat.
So far we have theoretically traced the evolution of the origi-
nal nebula into a system of thin, hot, and bright gaseous planets
revolving around a huge gaseous centre. This central conden-
sation was even hotter than the planets, and was destined in
time to become a central sun, luminous with an inconceivable
intensity of heat.
The small amount of nebulous matter which still remained,
outside the planetary centres, was gradually drawn in by them
in a spiral manner, and condensed into similar but smaller
centres. They acquired the same peculiarities of revolution
and rotation, and in fact repeated the original history of the
whole system on a smaller scale. This appears to be the origin
of the satellites which now attend the larger planets, and of the
rings of Saturn, which consist of innumerable small satellites.
After a certain amount of condensation the production of
frictional heat in each subordinate centre became less in
amount. As the radiation continued unchecked, a maximum of
heat was reached, and the satellites and planets then began
to cool off. The smaller a body is, the larger becomes its
surface in proportion to its mass. The satellites and smallest
planets therefore cooled off the quickest. Their surfaces solidi-
fied and became solid rock. This, being a bad conductor of heat,
somewhat checked their loss of heat by radiation, but did not al-
together prevent it. In time they therefore became solid to
the centre and gradually approximated to the temperature of
outer space.
The larger planets are now going through the same cooling
MODIFICATIONS OF THE NEBULAR THEORY
and solidifying process. But the central Sun is still producing
about as much heat by its contraction as it loses by radiation
into outer space. It is still kept in an incandescent gaseous
form by this heat, and the only elements in it which have
reached a solid state are the carbon and silicon which are ex-
posed to the cold of outer space above a certain elevation in
its atmosphere of metallic gases. Their chilled particles are
apparently frozen into solid incandescent beads that form the
glittering clouds which we term the solar photosphere.
We thus see that the heat of the Sun is not due to com-
bustion. In fact combustion is like organic life, it cannot
exist above or below a certain range of temperature. The heat
of the Sun is at present far too great to allow a comparatively
cold process like combustion to take place anywhere near it.
When the Sun formed the bulk of the original nebula its
energy was all potential. Its circling particles have been
falling ever since, as they " spirated " around the centre of
gravity of the mass. Their friction in falling is the cause of
all the heat, etc., which has since been produced and radiated.
The same amount of heat is produced by the friction of adja-
cent particles, whether a body falls rapidly or slowly, directly
or indirectly. As the Sun's mass has not changed and is
known, the amount of potential energy changed into actual
energy can be computed. The radiant energy developed by
the contraction of the Solar System from a thin nebula is equal
to the energy necessary to force its particles asunder and return
it to a nebular condition.
After the contraction had gone on for many millions of years,
the various planets were left outside of the central condensing
nucleus in the way already described. When this nucleus
had contracted to the size of the Earth's present orbit, it was
still about 12,000 times thinner than our atmosphere at the
sea level. It was therefore about as dense as the most perfect
vacuum we can make with an air-pump. As it continued to
shrink in size, the crowding atoms gradually gave rise to long
heat-waves. In the course of ages the short light-waves were
HOW TO KNOW THE STARRY HEAVENS
also produced, turning the gaseous mass into a nebulous sun.
It has been estimated that when it had contracted to the size
of the present orbit of Mercury it gave off about one eightieth
of its present radiant energy, and when the continuous con-
traction had reduced it to a thousand times its present size its
average density became equal to that of our atmosphere at the
sea level.
As the light gases around it were gradually absorbed, it
slowly changed from a nebulous star into a brilliant bluish-
white star, and afterward into a yellowish-white one. It is
now, on the average, about one and a half times as dense as
water. Its particles, therefore, fall more slowly, but produce
more friction and radiance.
The Sun's contraction in size has now fallen off to about
9 inches per day say a mile in twenty years. This is so
small that it would take nearly 10,000 years to recognise the
shrinkage, from the Earth, with our present instruments. The
maximum of heat appears to have been passed, and the light
has begun to wane and turn yellow. Some day, in the dim and
distant future, spasms of chemical combination will take place
in the reddening Sun. It will gradually liquefy from the
centre up to the surface, and afterwards solidify from the sur-
face down to the centre. It will then cease to contract and to
give out light and heat, its potential energy having all turned
into actual energy, and radiated away into space. By that time
its average density will have probably increased to about twenty
times that of water.
Although satellites or moons are common in the Solar System,
our Moon appears to be, in some respects, an exceptional one.
It is very much larger, in proportion to the Earth, than the
satellites of the other planets "are when compared with their
primaries, and it appears to have had a different origin. Before
it was born, the still molten Earth appears to have shrunk
until it rotated in about four or five hours. Its equatorial parts
then bulged out and became almost weightless, through the
centrifugal force resulting from the rapid rotation. The pull of
MODIFICATIONS OF THE NEBULAR THEORY 213
the Sun on this weightless mass raised a huge tide on the Sun-
ward side of the Earth. This gradually grew in size, so that
the Earth assumed something of a pear shape. Finally the
rotation became so rapid that the tidal wave was wrenched
loose from the main body of the Earth and became our Moon.
This tidal parentage is known as a " fission " process, and was
first brought to light by Professor George Darwin.
The Earth and Moon, while still very close together, and
still molten, produced huge tides in each other. The Earth-
raised Moon-tides acted as a brake on the Moon and checked
its rotation. At last its rotation and revolution periods became
equal, so that it always turned the same face to the Earth.
The Earth-tides which the Sun and Moon raised acted as a
brake on the Earth itself, and at the same time quickened
the forward motion of the Moon, thereby increasing its distance
and period.
The Earth and Moon have now solidified, so that the tides
on the Moon have ceased, and those on the Earth are almost
FIG. 95. EARTH-TIDES, IF THE DAY AND MONTH WERE EQUAL
The moon's orbit would remain constant.
entirely confined to the large open bodies of water on its sur-
face. Yet the ocean tides still continue to act as a brake to
check the Earth's rotation. The effect, though small, is cumu-
lative, and will in time lengthen the Earth's day and the
Moon's " moonth " till they are both equal to about 55 of our
days. The lengthening will then cease, and both bodies,
though still revolving around their common centre of gravity,
214 HOW TO KNOW THE STARRY HEAVENS
will be relatively immovable, like the two ends of a dumb-bell,
which always present the same face to each other.
It is not difficult to understand that the tides on each body
should act as a brake and check rotation. But it is not so
obvious that the Earth- tides should pull the Moon forward,
and, by so doing, increase the size of its orbit and the period of
its revolution. The principle is as follows :
A particle of matter at the centre of the Earth is pulled
toward the Moon with a certain force. A particle on the side
nearest the Moon is pulled with a greater force. And a parti-
CUtt-TAttion
)MOON
FIG. 96. ACCELERATION OF MOON BY FORWARD PULL OF EARTH-TIDE
Moon's orbit forms a slowly opening spiral.
cle on the side away from the Moon is pulled with less force,
and is therefore (relatively) repelled. Consequently, if the
Earth rotated at the same speed at which the Moon revolved,
the water would bulge out, not only on the side nearest the
Moon, but also on the side farthest from it (see Figure 95).
Owing, however, to the relative rapidity of the Earth's rota-
tion, the tides are dragged forward by molecular friction. The
tide nearest the Moon is therefore a little in front of the line
joining the centres of the Earth and Moon (see Figure 96).
It is the forward pull of this Earth-tide on the Moon which
quickens the motion of the latter. By so doing it very slowly
enlarges the Moon's orbit and lengthens its period of revolution
around the centre of gravity of the Earth and Moon. The
action (like that of the Earth-brake) is absolutely imperceptible,
MODIFICATIONS OF THE NEBULAR THEORY 215
but is, at the same time, real and cumulative. It is therefore
only a question of time for great changes to be produced. And
of time there is no end. 1
By the time the Earth and Moon have reached the dumb-
bell stage, the lunar tidal-friction on the Earth will come to an
end, and the Moon's path will cease to be an opening spiraL
FIG. 97. LOOP IN APPARENT PATH OF MARS
As he approaches opposition, his direct (easterly) motion amongst
the stars slackens and soon ceases. He then appears to move back
towards the west. After opposition this retrograde motion also slack-
ens and ceases. His direct motion then recommences, and is kept up
till the next opposition. He thus appears to make a loop every 584 days.
But until our oceans are frozen solid, the Earth's solar tides
will still continue to act as a brake and check its rotation. So
at last the time may come when the Earth's day will equal its
year, and the same side will always be turned toward the Sun. 2
It is rather uncertain what changes will take place after this
stage has been reached. If no accident should happen, in the
form of a collision with some outside body, the probability is
that the satellites and planets will very slowly draw in toward
their centres of revolution. 3 In this case the Moon's path will
1 The tide which is away from the Moon tends to counteract this pull, but is
too weak to overcome it altogether.
2 Mercury and Venus appear to have already reached this stage.
8 This theory is based upon the supposition of a resisting medium, ethereal or
otherwise.
216 HOW TO KNOW THE STARRY HEAVENS
gradually get smaller, and it will, in time, reach the surface of
the Earth. The two bodies will grind each other into super-
heated gas, which will afterward cool down and solidify. The
resulting body will gradually get nearer to the Sun, and even-
tually grind its way into the body of its parent. 1
By the time all the planets have returned to the Sun, and
the last disturbance has subsided, one second of Eternity will
w
FIG. 98. DIAGRAM SHOWING CAUSE OF LOOP IN APPARENT PATH OF MARS
The positions of Earth and Mars given at intervals of ten days. Mars appears to ad-
vance amongst the stars from 1 to 7, to retrograde from 7 to 11, and then to advance as
before.
have passed away since it was in the same stage before. The
Solar System will then be represented by a cold, dark, solid
mass containing the same amount of matter as the original
nebula. This dead hulk will drift around in the long cold star-
light night (like a derelict on the broad ocean) until some simi-
lar body collides with it and turns it all into gas again. It will
1 If this theory is correct, the matter of which our bodies are composed once
formed part of what is now the Sun, and will in time return to it.
MODIFICATIONS OF THE NEBULAR THEORY 217
then be ready to live its life over again and give birth to an-
other Solar System perhaps twice as large as the present one.
These cycles will presumably take place an infinite number of
times, the same matter being used over and over again to all
eternity. This is probably true not only of the future but of
the past ; not only of our System but of all the systems of the
Universe; not only of our Universe but of all the universes
that may exist in infinite space.
Now that I am through with the Nebular Hypothesis, it may
be well to remind the reader again that it is still an unproved
theory. As a working hypothesis it is one of the grandest and
most valuable theories ever reasoned out by the mind of man,
and in its main features it is almost certainly true as far as it
goes. But from the very nature of the case we are not in a
position to prove its truth, and it is doubtful if we ever shall
have anything except indirect evidence concerning it.
SUMMARY
I cannot do better than close this chapter with a summary,
by Ernst Haeckel, of the most important conclusions at which
science is arriving with regard to the constitution and evolu-
tion of the Great Cosmos. It is as follows:
" I. The extent of the Universe is infinite and unbounded ; it is
empty in no part, but everywhere filled with substance.
" II. The duration of the Universe is equally infinite and unbounded;
it has no beginning and no end : it is eternity.
II III. Substance is everywhere and always in uninterrupted move-
ment and transformation : nowhere is there perfect repose and rigid-
ity ; yet the infinite quantity of matter and of eternally changing
force remains constant.
" IV. This universal movement of substance in space takes the
form of an eternal cycle or of a periodical process of evolution.
" V. The phases of this evolution consist in a periodic change of
consistency, of which the first outcome is the primary division into
mass and ether, the ergonomy of ponderable and imponderable
matter.
218 HOW TO KNOW THE STARRY HEAVENS
" VI. This division is effected by a progressive condensation of
matter as the formation of countless infinitesimal ' centres of conden-
sation,' in which the inherent primitive properties of substance feel-
ing and inclination are the active causes.
"VII. While minute and then larger bodies are being formed by
this pyknotic process in one part of space, and the intermediate ether
increases its strain, the opposite process the destruction of cosmic
bodies by collision is taking place in another quarter.
" VIII. The immense quantity of heat which is generated in this
mechanical process of the collision of swiftly moving bodies represents
the new kinetic energy which effects the movement of the resulting
nebulae and the construction of new rotating bodies. The eternal
drama begins afresh." *
1 " The Kiddle of the Universe," pp. 242, 243.
CHAPTER XIX
THE MESSENGERS OF HEAVEN
" In the old mythologies the Universe consisted merely of a flat World, resting
on an infernal bowl, and covered by a celestial vault or canopy.
" The Gods who ruled this mundane Universe generally resided on the top of
the firmamental dish-cover. There the supreme Deity had his throne, and pre-
sided over the councils of the Gods.
" As none of these Gods were omniscient or omnipresent, they had to provide
themselves with angelic messengers to keep them posted as to what was going on
iii the World beneath, and to carry out their commands when they had come to
an agreement as to what kind of left-handed justice should be meted out to the
mortals below.
" These messengers of heaven were no loafers round the throne when they had
a duty to perform. They could fly on the wings of the wind and outstrip the
fiercest tempest.
" We now know that these angelic messengers, like the Gods they were supposed
to serve, have no existence except in the imaginations of ignorant and superstitious
people. But Science has revealed to us that there are messengers of heaven more
swift than the wing-footed Mercury, more restless than the cloven-hoofed Satan,
and more long-lived than the Father of the Gods himself." A. Zazel.
VISITORS FROM AFAR
IN a former chapter I spoke about the intense loneliness of
our Solar System in the midst of an immense multitude of
similar systems scattered through space.
Is there, then, no physical communication between the vari-
ous systems of worlds ? Are they entirely and for ever cut off
from one another? Are there no messengers of heaven that
can serve the bidding and carry the messages of the sunny-faced
Gods of ethereal space ?
Yes, there are wanderers who go from star to star and from
constellation to constellation. There are beings which spend
almost an eternity in going to and fro in the Universe, and in
flying up and down through it.
220 HOW TO KNOW THE STARRY HEAVENS
A VOYAGE OF FIVE MILLION YEARS
In order to learn something of these interstellar wanderers,
let us suppose that we are back in our Chariot of Imagination,
half way between our Sun and the nearest outside star. Let us
also suppose that the clock has been turned back several
millions of years ; that we have plenty of time at our disposal ;
and that we have laid in a goodly supply of Job's patience.
We are surrounded, as before, by countless systems of worlds,
but they are all in the remote distance. Let us move around
a little, and see if our immediate neighbourhood is really as
empty as it seems.
With the naked eye we might have to look for a long time
before finding anything near us. But with suitable instruments
we soon find that although there are no suns or large worlds in
our neighbourhood there are, here and there, small fragments of
hard rock floating in the otherwise empty darkness. These
stones sometimes contain a large percentage of iron, and greatly
resemble the meteoric stones that occasionally fall onto our
Earth. They vary greatly in size, some of them being no larger
than grains of sand. As there is no large world near to attract
them, they are destitute of weight and simply float in empty
space.
If we search long enough we may possibly come across one or
two similar rock masses of considerable size, for there does not
appear to be any break between these " pocket-planets" and the
huge suns and worlds with which we are distantly acquainted.
In some places these airy particles of sand and gravel are
thousands of miles apart, but sometimes they are so crowded
together that they are only twenty or thirty miles from one
another.
As these fragments of floating rock are familiar in appearance,
small in size, non-aggressive in disposition, and sedentary in
habit, we will not concern ourselves any more with them at pres-
ent, but will stop in one place and sweep the neighbourhood with
a searchlight to see if anything more important passes our way.
THE MESSENGERS OF HEAVEN
We may have to watch for what seems to us a big part of
eternity, or our search may be successful before an earthly year
has passed away.
At last our patience is rewarded by seeing something coming
in our direction. It is approaching so leisurely that we have
plenty of time to observe it, as it almost imperceptibly drifts by
our lonely station.
With the help of suitable instruments we can see that our
visitor consists of a nucleus of fragmentary solids surrounded
by a thin but misty atmosphere which emits a faintly phos-
phorescent glow. The density of the whole mass is so small
that the solid nucleus is apparently in the form of dust or ashes,
with perhaps a nucleolus of larger fragments. All are practi-
cally without weight, and rest on one another
as gently as so much feathery down.
Our visitor is not very far away from us, as
celestial distances go, and yet it appears to
be almost at a standstill. Considering its
size it really seems to be the quietest, laziest,
deadest object we have yet come across in the
Universe. With the exception of the tiny ^ 99. A CELES-
meteoric stones just mentioned, we have never TIAL MESSENGER ON
seen its equal in these respects.
Let us follow this strange object in its do^iVpSntta^Vei^
leisurely travels through space. But be care- ula - it should be viewed
, , J . . r . , from a distance.
lul lest your impatience at its slowness does
not bring on that kind of nervous attack which is known by
western deer-hunters as the "buck-ager," for you might pos-
sibly scare the lazy-looking object, which is not as dead as it
looks, and is indeed capable of travelling at a speed that would
almost leave the Chariot of Imagination behind.
After keeping the new arrival in view for a million years or
so, it becomes evident that its drifting motion is not due to any
energy of its own, but is caused by the gravitational attraction
of the far distant stars.
HOW TO KNOW THE STARRY HEAVENS
KEARING PORT
In the course of long and weary ages the object we are
investigating gradually and imperceptibly enters the area
where the attractive energy exerted by one star is greater than
that of all the other stars put together. The result is that it
now moves faster than before, and (like a messenger-boy near-
ing his destination) begins to look as though it were going
somewhere.
It yields itself without a struggle to the growing influence,
and imperceptibly quickens its speed with every mile it goes.
As the time passes away, the now progressive messenger leaves
the cold and midnight darkness of outer space, and enters the
serene twilight that reigns eternal at the portals of the solar
system it is visiting.
As it approaches the brilliantly glowing star and comes within
the radius of its circling family of worlds, it increases still more
the rapidity of its forward movement. Faster and yet faster it
speeds through the gathering light. The intense cold of inter-
stellar space has now moderated. The new arrival feels the
growing warmth, and begins to unfold itself before the cheerful
influence. The surrounding haze gradually melts away into a
glowing gas which forms a huge luminous atmosphere around
the loose and scattering nucleus.
By this time the outer members of the solar family have been
safely passed. The now rushing messenger is hastening faster
and yet faster toward the central star. The milestones of space
fall behind as the pickets of a fence flicker when seen close at
hand from an express train.
The so-called Asteroids are passed with a fearful disregard
for possible collisions. Then, with still gathering intensity of
ever-increasing speed, our celestial messenger flashes like a
winged sword of fire through the midst of the inner planets as
they circle serenely around their central sun. So great is the
speed of the messenger's body that its flowing robes of luminous
particles now trail behind for many millions of miles. They
FIG. 100. A CELESTIAL MESSENGER APPROACHING A STAR
FIG. 101. BROOK'S COMET, 1893
Lick photograph. The tail was distorted, probably
by collision with a swarm of meteoric bodies.
FIG. 102. COMET 1903 C
Lick photograph.
THE MESSENGERS OF HEAVEN 223
look, indeed, like the " wake " of a fast-moving steamer on
smooth water (see Figure 100).
A CELESTIAL MESSENGER APPROACHING A STAR
The inhabitants of the minor planets tremble by night as
they see what looks like a mighty two-edged sword of fire
flaming in the starlit sky. Some of the more ignorant of
them pray to their Gods to deliver them from the threatening
monster. Others, with more self-reliance, beat their tom-toms
to scare away the intruder from their neighbourhood. But, all
unconscious of the commotion it has caused among the self-
important microbes that cling around the circling cobble-stones,
the mighty visitor sweeps majestically by on its appointed
path, leading to the central star.
A HOT RECEPTION
At last, with a still more energetic rush that almost rivals
the flight of the swift- winged arrows of light, the messenger of
the Gods swoops down down down, and is lost to sight
in the blasting heat and dazzling light of the solar furnaces.
To all appearances our messenger of the Gods has met with
such a fiery reception that his reappearance is not to be looked
for. His fall seemed to be as disastrous as that of the fabled
Adversary, whom (according to Milton)
"the Almighty Power
Hurled headlong flaming from the ethereal sky,
With hideous ruin and combustion, down
To bottomless perdition, there to dwell
In adamantine chains and penal fire,
Who durst defy the Omnipotent to arms." l
One thing, however, we noticed as our celestial messenger
disappeared in the solar light, and that was that he did not fall
prone into the solar flames, as the traditional Adversary crashed
into the molten crater of the hellish Kilauea. He seemed, in-
1 " Paradise Lost," Book I.
224, HOW TO KNOW THE STARRY HEAVENS
deed, to fall to one side, as though he meant to skim along the
surface, deliver his message, and rush out on the other side
before the terrific heat could burn him up.
Knowing, however, how fearful is the heat of that stu-
pendous globular furnace, it does not seem worth while staying
to see if he has survived the ordeal. Indeed, it is uncomfort-
ably hot even fifty millions of miles away from the blazing
star. We shall have to back out of the stellar heat lest our
Chariot of Imagination should catch fire, or we should lose
control of the horses thereof and share the fate of the presump-
tuous Phaethon when he tried to drive the chariot of the Sun.
ANOTHER VOYAGE
But stay ! Something has just come into sight on the other
side of the star. What is it ? Surely it cannot be that our
messenger has safely skimmed the vast and fiery furnace, and
has already reappeared on the other side, a million miles away
from where he disappeared but an hour ago ! It seems im-
possible, and yet it is evidently the same messenger, hasten-
ing away in safety from the fiery ordeal through which he has
passed.
So far from being injured by the encounter, he (like the
grand hero of " Paradise Lost "),
" With fresh alacrity and force renewed,
Springs upward, like a pyramid of fire,
Into the wild expanse, and through the shock
Of fighting elements, on all sides round
Environed, wins his way ; harder beset
And more endanger'd than when Argo passed
Through Bosphorus, betwixt the justling rocks;
Or when Ulysses on the larboard shunn'd
Charybdis, and by the other whirlpool steered." 1
Strange to relate, our fast-retreating messenger has been
beaten in the race by his flowing garments. These, instead of
trailing behind in the solar furnaces, are now extended in front
1 " Paradise Lost," Book II.
THE MESSENGERS OF HEAVEN 225
of him for many a million miles, as though anxious to get
back into the outer cold and darkness.
Let us turn our chariot and trace him as he recedes from the
star. We have not followed him very far before we find that
his speed begins to slacken, and that he is apparently gathering
in his garments. By the time that we are once more in the
dark, outside the stellar system, he is again nothing but a
round mass of faintly glowing haze, drifting idly through the
midnight sky.
So he keeps on, century after century, drifting drifting
drifting, like a ship becalmed by night in the solitude of a
tropic sea.
On our little Earth and perhaps on millions of similar
worlds scattered through space continents appear above the
seas and are pounded to pieces by the waves. New and higher
forms of life develop, and give way in their turn to still more
specialised species. The huge reptiles of the Earth's Oolite
yield to the warm-blooded mammalia of the Tertiary period.
The four-footed tree-dwellers develop ape-like peculiarities.
The sharpest of the four-handed apes desert the trees and adapt
themselves once more to live on the ground. Pithecanthropus
erectus develops into Palaeolithic Man. Neolithic Man is
driven into the mountains by those who have chariots of iron.
Nations, empires, and races come into existence, nourish for a
time, and pass away, like ephemeric clouds in a summer sky.
The chattel-slave and his master develop into the serf and his
lord. The wage-slave and his " boss " become economic equals
in the Industrial Commonwealth. And still this hazy mass is
drifting drifting drifting, through ethereal realms of star-
lit space.
A million times our World goes around its Sun, and still our
lazy messenger is imperceptibly drifting through endless night.
For two three four five millions of Earth-timed years
he drifts drifts drifts along, and then, coming once more
under the influence of a star, he repeats his former rush, but
around another sun. Again he goes into the outer darkness,
15
226 HOW TO KNOW THE STARRY HEAVENS
drifts through almost endless years, and again he rushes around
another star. And so he spends what seems to us almost an
eternity of time.
A CAPTIVE MESSENGER
Sometimes the influences which surround a star cause him
to close his orbit and circle around and around the same star in
a long narrow orbit. But some time or other the attraction of
a planet turns him out of his closed orbit, and he once more
goes off and drifts drifts drifts through endless space.
COMETS
It is hardly necessary to state that our Messenger of the
Gods is nothing more or less than what is known to us as a
comet. Such bodies exist throughout the Universe in hundreds
of millions. Until recently we were entirely in the dark as to
their composition, origin, and movements. Their nuclei, it is
true, were known to submit to the law of gravitation, but
hardly a guess could be made as to the nature of the repulsive
force which produces and dominates over their tails. Even yet
we have much to learn concerning comets generally. But some
of the main facts have been ascertained, and a reasonable
theory has been formed which throws a good deal of light
upon them.
The probability is that they are huge collections of loose
meteoric dust and gravel, with large quantities of hydrocarbons
and free hydrogen. All this loose material has been ejected
into space from solar or planetary volcanoes. In the intense
cold of outer space (which is at least 230 below zero on the
Fahrenheit scale, and may possibly be 461), the hydrogen
and hydrocarbons naturally cling evenly around the solider
material.
On approaching a star, the radiant energy from the central
sun causes them to spread in all directions around the scatter-
ing nucleus. They thus form the cloudy haze of which all
THE MESSENGERS OF HEAVEN 227
telescopic comets consist. When still nearer, the spreading
particles in front are further dissipated by the heat. At last
they are so small that the radiant energy of the sun overcomes
their gravity, and violently repels them into outer space.
There, lighted up by the sun, and glowing with a soft electric
light of their own, they form the tremendous hollow luminous
FIG. 103. PARABOLIC ORBIT OF A FREE COMET
It is practically an ellipse with the two foci at an infinite
distance from each other. Hence the orbit is closed at only
one end.
trumpet-shaped appendage known as the tail of the comet.
The shape of the tail, and its direction in space, depend on the
strength of the repelling force, and that varies with the size of
the particles composing the tail. Sometimes there are several
tails, extending in different directions, or, rather, in different
curves. There appear to be three different types of tail, differ-
ing in direction, shape, and material. The straightest ones are
probably composed of hydrogen. They are repelled with the
greatest force, and therefore extend almost directly away from
the Sun. The next are more curved, and are supposed to con-
228 HOW TO KNOW THE STARRY HEAVENS
sist of varying hydrocarbons. They are repelled with about
one quarter the force of the hydrogen tail. The third type is
still more curved, and probably consists of chlorine and iron.
The repulsion is only about one sixteenth that of the hydrogen
tail. All of these tails are hollow cones, of which only the
sides are generally visible.
FIG. 104. ELLIPTICAL ORBITS OF CAPTIVE COMETS
As fresh particles are being sent out into each tail all the
time, it naturally follows that after the head of the comet has
begun to recede from the Sun its newly formed tails stretch out
in front of it. In the meantime the old ones have been driven
off and dispersed.
As before stated, the main body of a comet obeys the same
laws that control the motions of all the heavenly bodies. The
luminous gas of which a comet is largely composed is so thin
and transparent when within the Solar System that the faintest
stars can be seen through millions of miles of its substance.
The whole comet is so light in weight that it can sweep by the
FIG. 106. DONATI'S COMET, 1858
By Bond. (From Comstock's " Text-book of Astronomy," published by Messrs. D. Appleton & Co.)
FIG. 107. COMET RORDAME, 1893
By Hussey, at Lick Observatory.
THE MESSENGERS OF HEAVEN
planet Saturn without disturbing the motions of his numerous
family of moons, while these same moons, small as they are,
are able to deflect it from its original path if it should happen
to pass near them.
PERIODIC COMETS
" Amid the radiant orbs
That more than deck, that animate the sky,
The life-infusing suns of other wcfrlds ;
Lo ! from the dread immensity of space,
Returning with accelerated course,
The rushing comet to the Sun descends ;
And as he sinks below the shading Earth,
With awful train projected o'er the heavens,
The guilty nations tremble." Thomson, "The Seasons" Summer.
Some of the comets that move in closed orbits around our
Sun have had their elliptical paths traced out by the astron-
omers. They are not confined to the Ecliptic, like the planets,
but are inclined at all angles
to it. Their regular coming can
be anticipated, though their
movements are never to be de-
pended on, owing to the ease
with which they are turned
out of their course by the plan-
ets they happen to come near.
Several of the periodical
comets have paths extending
,, , ., \ . _. 6 FIG. 105. TAIL OF A COMET NEAR
to the orbit of Jupiter. Others PERIHELION
go away as far as Saturn and
Uranus. This is one of the peculiarities which gave rise to
the theory that they were originally thrown out from those
giant planets by tremendous volcanic eruptions, like those
which are constantly taking place on the apparent surface of
our Sun. This theory is now generally abandoned, on account
of the tremendous force necessary to overcome the gravitation
of such huge planets.
They are now believed to have been captured by the planets
230 HOW TO KNOW THE STARRY HEAVENS
to which they are related. Tempel's comet, which is connected
with the Leonid meteors and which goes away as far as the
orbit of Uranus has had its orbit traced back to the year
126 A. D. At that date the two bodies were very near together,
and the planet appears to have drawn it (and the Leonids
accompanying it), out of the original parabolic orbit into an
elliptical orbit having a period of about 33 years. Such
changes of orbit appear to be not uncommon among comets.
The spectra of comets .contain three bright hydrocarbon
bands well denned at the red end. There are also several
bright iron lines, and one due to manganese. When a comet is
near the Sun, the bright sodium lines are sometimes seen. In
addition to this emission or radiation spectrum, there is
generally a faint absorption spectrum visible, with dark lines.
METEORS
Another peculiarity of these erratic wanderers is that some
of them are intimately connected with meteor showers. When
FIG. 108. A METEOR BURSTING IN THE ATMOSPHERE
Seen through a telescope.
our Earth passes through the path of one of these captive
comets, vast multitudes of so-called " shooting-stars " enter our
atmosphere and burn up with the heat generated by atmospheric
friction. Where fragments of meteors happen to reach the.
THE MESSENGERS OF HEAVEN 231
surface of the Earth, they are found to consist of volcanic sub-
stances like those thrown out by earthly volcanoes. Many of
them consist of irregular fragments cemented together. Some
contain considerable iron, and carbon has been found in a few.
Even mineral veins have been found in them.
Our Earth has now lost a great part of its volcanic activity,
yet the eruption of Krakatoa, a few years ago, was almost
powerful enough to cast its debris clear of the planet's
attraction.
Supposing such a thing to take place, the cast-out masses,
both gaseous and solid, would naturally turn toward the Sun,
rush around that mighty globe, and, if not consumed by its
heat, return to the place where the Earth was when they were
ejected. Not finding the planet where it had been, the stream
of meteoric matter would naturally turn to the Sun again, and
continue in the same orbit until its Earth-derived particles were
all picked up again by the Earth or Moon.
If these comets and clouds of meteoric dust should originate
in the way described, it follows that moderate-sized worlds of
other systems must be equally capable of casting out similar
masses of cometary gas and meteoric solids. This would explain
the great abundance of comets and meteoric streams in our own
system.
There is some evidence that both comets and meteoric streams
gradually waste away when travelling through solar systems.
At each approach to a star, a comet appears to lose the repelled
matter which forms its dissipated tail or tails. After a certain
number of perihelia the supply of hydrogen and hydrocarbons
fails. Short-period comets are therefore generally tailless. A
comet has also been known to split up into two separate bodies
which gradually drifted apart. In some cometary orbits there
appear to be several comets, all moving in the same path, but
at long distances apart. Sometimes the solid bodies forming
the nucleus of a comet appear to spread out along its orbit until
the comet disappears and nothing remains but a long trail of
invisible meteoric matter. Meteoric streams also waste away
232 HOW TO KNOW THE STARRY HEAVENS
to some extent, owing to the capture or deflection of fragments
by passing planets. The captured fragments of course form the
meteors and " shooting-stars " with which we are so familiar on
Planet Number Three.
It seems, therefore, that, long-lived as the comets are, they
too have a limit in duration. They are not " built for eternity,"
but are as ephemeral as the suns and worlds among which they
wander. But the loss is evidently made up by the constant
formation of fresh comets and meteoric streams in various parts
of the Universe.
CHAPTER XX
LARGE AND SMALL WORLDS
" There are worlds so vast that beside them our Earth would seem but a toy.
There are worlds so small that they might serve as marbles for our children to
play with." A. Zazd.
IT has been already shown that both suns and worlds vary
enormously in size and in the amount of matter they con-
tain. But it is very hard to realise how vast these differences
are. In our own System, while some planets are immensely
larger than our Earth, others are too small to be visible with
any telescope unless they happen to be massed together in mil-
lions, as in the rings of Saturn. It may be well to illustrate
some of these differences, paying special attention to the Third
Planet, the largest planet, and the Sun.
MICROSCOPIC WORLDS
There are " planets " going around the Sun which are so small
that if we had them in our hands we could not see them with-
out a microscope. They are commonly called meteoric bodies,
yet they really and truly are worlds like ours, revolving in or-
bits more or less similar to ours. They are subject to the same
laws, and may have had a separate existence as long as the
Earth on which we live.
At the same time there are planets, going around the same
Sun, so vast that our Earth would appear utterly insignificant
beside them.
OUR INSIGNIFICANT EARTH
Jupiter, the largest planet in our system, weighs 300 times
as much as our Earth. Not having yet cooled down so much
as the Earth, it is more than 1,200 times as large.
234 HOW TO KNOW THE STARRY HEAVENS
Our Sun weighs 330,000 times as much as the Earth, and
for the same reason is 1,250,000 times as large.
Two or three illustrations may make these comparisons
plainer.
If our Earth be represented by a ball one inch in diameter,
Jupiter's weight will be represented by a globe, of the same
SATURN.
* 9 f| @ 6
ASTEROIDS. MARS. MOON. EARTH. VENUS. MERCURY.
FIG. 110. RELATIVE SIZES OF PLANETS
density, 4.2 inches thick, and that of the Sun by a globe 5 feet
9 inches across.
With the same one-inch ball for our Earth, Jupiter's size will
be represented by a globe 11 inches thick, and that of the Sun
by a globe 9 feet across.
If we were to place in a straight line enough of these one-
inch globes to represent the weight of Jupiter, they would
extend 25 feet, while if we were to put in a line enough to
represent the size of Jupiter, they would reach 100 feet.
To represent the Sun's weight in the same way, we should
LARGE AND SMALL WORLDS
235
reguire a string of them more than five miles long. And for
its size, nearly twenty miles of them.
The difference between the mass of the Sun and that of the
Earth may also be illustrated in this way. A weight dropped
from a height on our Earth falls a little over 16 feet in the first
second. But on the Sun it
would fall 452 feet in the
same interval of time. An ob-
ject which, on account of the
Earth's attraction, here
weighs one pound, if removed
to the apparent surface of
our Sun, and weighed by a
spring balance, would be
found to have increased its
weight to 28 pounds on ac-
count of the greater mass
and attraction of the Sun.
These two illustrations do
not really do justice to the
difference between the mass
of the Earth and that of the
Sun. For the Sun's centre of
attraction is 108 times as far
from the object on its surface
as in the case of the Earth.
To get over this difficulty, let us imagine the Sun to be com-
pressed until it is the same size as the Earth, without dimin-
ishing its mass. It will then be 330,000 times as dense as the
Earth. The object which, on the Earth, weighed a pound, will
now, when removed to this compressed Sun, be found to weigh
165 American tons. And a weight dropped from a height will
fall 1,000 miles in the first second. 1
1 This compressed illustration is of course impossible, but it will serve to show
the immense difference in the quantity of material contained in the Earth and
Suu.
FIG. 111. RELATIVE SIZES OF SUN,
JUPITER, AND EARTH
236 HOW TO KNOW THE STARRY HEAVENS
All the other planets in our System, taken together, weigh
about 450 times as much as our Earth, yet the Sun outweighs
them all 745 times. If all the planets be represented by a
heap of boulders weighing 450 pounds, a little one-pound pebble
will stand for the Earth. And on the same scale the Sun will
be represented by a mighty rock weighing about 170 American
tons.
Our Moon is 2,162 miles in diameter, and looks, from here,
as though it were the same size as the Sun, yet the latter ex-
ceeds it in bulk more than
60,000,000 times, and in weight
27,000,000 times.
Go out on an unusually clear
night, when the Moon is below
the horizon. Notice what a
multitude of stars can be seen
by the naked eye alone. Imag-
ine every star visible to be 600
times as large as our Earth.
Then all of them rolled together
into one vast globe would not
be as large as the Sun.
Yet our Sun is comparatively
a small star. Canopus, one of
the bright stars in the southern
hemisphere, gives out many
thousands of times as much light. If its lustre is equal to that
of the Sun, it must be many thousands of times larger.
FIG. 112. RELATIVE SIZES OF THE
FIRST FOUK ASTEROIDS AND THE
EARTH'S SATELLITE. BY BARNARD
The black circle represents the Moon,
and the white ones the Asteroids.
OUR MIGHTY GLOBE
We thus see that our planet is a very insignificant world
compared with some of the other heavenly bodies. Yet it con-
tains what seems to us to be a considerable amount of material.
Let us suppose the Earth to be drawn out into a long square
column a mile thick each way. This column would reach from
LARGE AND SMALL WORLDS 237
the Sun to a distance 93 times as great as that of the planet
Neptune.
Let us suppose that this long column was put on suitable
flat-cars and started off at 50 miles an hour. Then suppose we
saw it coming, and decided not to cross the track till it had
passed by. We should have to wait 590,000 years before 'the
line would be clear.
A signal-light flashed from one end of this train, at the usual
speed of 186,000 miles in a second of time, would not be seen
at the other end for sixteen days.
If our Earth could be crushed under foot till it was flattened
out, so as to be only a mile thick, it would form a round flat
disc, 565,000 miles across, considerably larger than the
Moon's orbit.
So that if our Earth is of but slight importance in the Uni-
verse, it must be admitted that it is a considerable size when
looked at from a human standpoint.
THE CRASH OF WORLDS
Theoretically, every atom of matter in the Universe influences
every other atom of matter in the Universe. And practically
it influences all within x millions of miles.
Yet as a rule the myriads of suns and worlds do not interfere
with one another. They keep on in the even tenor of their
way from century to century. For many ten thousands of
millenniums they keep out of one another's way.
Still, accidents will happen even among solar systems.
There appear to be times when suns and planets come into col-
lision, when even worlds suffer shipwreck.
Some of the stellar systems are drifting along at the rate of
two hundred miles in one second of time. Therefore such catas-
trophes are liable to give rise to a considerable amount of light
and heat.
Whenever you see what is miscalled a shooting -star dart
across the sky and disappear, you witness the destruction of a
" pocket-planet " which may be as old as our Earth.
238 HOW TO KNOW THE STARRY HEAVENS
Whenever you see the fiery rush of a meteor, and hear its
distant crash, you may know that another little world has met
its doom and ceased to have an independent existence.
Whenever a star suddenly increases in brilliancy, and for a
time gives out many thousands of times its former light, you
may feel tolerably certain that mighty suns have crashed into
mutual destruction.
Yet nothing is really destroyed. The " shooting-star " still
exists as vapour or dust in our atmosphere ; the meteor settles
down to form part of oUr Earth; the crashing suns, though
turned to naming gas, unite and begin once more the same end-
less cycle of evolution and devolution. There is no end, nor
was there yet beginning.
STARS ARE SOLITARY
" His soul was like a star, and dwelt apart."
Many people still have the old idea that the stars, although
a long way from us, are comparatively close to one another.
This is not at all correct, in spite of the fact that in thousands
of cases two, three, or more stars form one system.
Some of the star-clusters appear to be democratic systems
composed of vast numbers of comparatively small suns revolv-
ing around their common centres of gravity. Thus the cluster
Omega Centauri consists of more than 6,000 stars, of which at
least 125 are variables (see Figure 94). In cases like this it is
not likely that the individual suns have planets revolving
around them, or, at least, not habitable ones.
But leaving these multiple systems out of consideration, it
may be said that each star is, with the exception of its subject
worlds, solitary in space. If we could take our stand at a com-
fortable distance from any one of these sovereign stars, we
should imagine the system to be in the centre of a huge void,
surrounded, at an enormous distance, by a hollow sphere of
crowded stars. Or, in other words, the heavens would look
about the same as they do from our Solar System. In the case
LARGE AND SMALL WORLDS 239
of a neighbouring star, only an expert could detect any changes
in the constellations.
When we see two stars which appear to be near to each
other, we must remember that in many cases one star is two,
ten, twenty, or a hundred times as far from us as the other one.
It may even be that the brighter one is the most distant.
On this account the apparent brightness of a star as seen from
our Earth is a very unreliable guide as to its distance or size.
As a matter of fact, no two stars are alike in actual size, bril-
liancy, colour, or any other peculiarity.
STABS ARE MIGHTY SUNS
" The stars of heaven fell to the ground, as green figs fall jvhen the tree is
shaken by a mighty wind." Rev. vi, 15.
Then we must remember that every one of these sovereign
stars is a SUN more or less like our Sun. Every one seen is at
least something like 1,000,000 times as large as our Earth.
The smallest visible is worthy of the name of SUN ; is large
enough, powerful enough, hot enough, and bright enough, to
hold sway over worlds as beautiful as Venus, as fiery as Mars,
as vast as Jupiter, as magnificent as Saturn, as distant as Nep-
tune, and as populous as the little Earth on which we live.
Every star visible is blazing with a light peculiar to itself,
different from the light of any other. In the vast majority of
cases this light is intense enough to make the Columbian
search-light look black by comparison.
Each of these suns is throbbing with quaking blasts of fer-
vent heat that would make the molten interior of a Bessemer
converter seem cold by comparison. The eruptions of Mont
Pe'le'e, fearful as they seemed to us, were but the sputterings of
a bunch of Fourth of July fire-crackers when compared with the
awful cannonading which goes on, every day in the year, all
around the average star.
So intense is the heat of our own central star that if the
Earth were to be checked in its career and left to fall toward
240 HOW TO KNOW THE STARRY HEAVENS
the Sun, it would never reach the photosphere in a solid state,
but would be turned into flaming gas, and driven off again, like
a hailstone falling toward a mass of molten steel. Sir John
Herschel showed that if an icicle 45 miles in diameter could
be driven endways into the Sun with the velocity of light
(186,000 miles per second), it would be melted off as quickly as
it advanced. Some of the larger stars could dispose of an icicle
more than 100 miles in diameter.
Every star is continuously roaring and throbbing with ear-
rending detonations and world-jarring convulsions that are
greater, in one short hour, than all our thunder and lightning,
earthquakes and volcanic eruptions, for millions of years gone
by. Every one is dragging its attendant family of worlds
through the wilderness of space at a speed that the mind of
man cannot realise, it is so tremendous.
A TINY GLOBE
"The Earth is my foot-stool." (The Later] Isaiah, Ixvi, 1.
In all this splendour of molten orbs, our Earth, fortunately
for us, has no part. Silent, dark, and invisible (except to three
or four of its nearest companions), it is of no measurable im-
portance in the economy of Nature. So far as other worlds are
concerned, its existence is no benefit, its disappearance would
cause no anxiety, its destruction would be no loss, its absence
would give no trouble.
Yet, fastened to the radiant skirts of the glorious Sun by
invisible yet unbreakable bonds, it has been dragged for many
millions of years, through the wilds of space, at a speed incon-
ceivably great. Small though it is, it is teeming with life of
every kind. It contains almost boundless oceans and con-
tinents. It has mountains and valleys, rivers and lakes, islands
and seas, beautiful beyond the power of words to describe. It
has a history extending back millions upon millions of years.
It has a future almost without end.
LARGE AND SMALL WORLDS
HUMAN ACHIEVEMENTS
So far I have considered only the smallness and insignificance
of man. But there is another side to the question. A thing
may be small and yet wonderful. The ancestors of man were
all Earth-born. He himself is but the creature of a day, and
has all his life been on one insignificant planet with no pros-
pect of ever leaving it. Yet, considering his situation, he has
done some wonderful things. Leaving out of consideration all
his earthly achievements, he has eaten of the fruit of the Tree
of Celestial Knowledge to a far greater extent than might have
been expected. Cooped up in his invisible cage, he has con-
templated the visible parts of the Universe to such good effect
that he has solved many of its mysteries. Not satisfied with
the eyes provided by Nature, he has constructed artificial
instruments which increase their light-grasping power more
than 40,000 times. With their help he is measuring the depths
of space, analysing the stars as though they were in his labora-
tory, weighing suns and worlds in a balance, and photographing
celestial objects that are invisible even with his instruments.
He traces the wanderings of the planets both in the remote
past and the distant future. He is finding out the life-history
of a sun from its cradle to its grave. He watches the stars so
closely that millions of them are unable to move without his
knowledge. The infinitely great and the infinitely small are
alike compelled to submit to his scrutiny. Slowly but surely
he is compelling Nature to give up her innermost secrets. He
is gradually solving the mystic riddle of the Universe.
These be no light achievements for man to have even par-
tially accomplished. The Gods of Greece and Eome never
attempted such tasks. Odin and Thor never dreamed of such
vast undertakings. The labours of Heracles and feats of Shem-
ishon cannot be mentioned on the same page without provoking
a smile. The actual achievements of man surpass those
fabulously attributed to the Gods and heroes of antiquity.
16
HOW TO KNOW THE STARRY HEAVENS
TWO STANDPOINTS
" The Hebrews looked upon themselves as Yahveh's Peculiar People, which
they probably were.
" The Chinese regard the ' Celestial Empire ' as the most important part of the
World, which it is to them.
" Every little Boston is thought, by its own people, to be the ' Hub of the Uni-
verse/ which it possibly may be to those that dwell therein.
"But a Citizen of the GREAT COSMOS though compelled to view all things
from his own physical standpoint can see them also from a spiritual standpoint
which is Universal and Eternal." A. Zazel.
To the ancients, the World was visible only from a local
standpoint, with the eyes of an epheineron. From their posi-
tion it appeared to be vast beyond comparison, fixed beyond the
possibility of removal, changeless as the decrees of destiny,
eternal as time itself.
We, who have eaten of the fruit of the Tree of Knowledge,
have acquired the power of observing the Earth from both a
local and a universal standpoint. We have learned of its
insignificance , yet we better comprehend its vastness. We
know that it is ever on the wing, yet we understand the un-
deviating fixity of the paths in which it travels. We watch its
lands and seas come and go like drifting clouds, yet we are
aware of the changelessness of the laws to which those changes
are due. We know it as a transient bubble on the River of
Eternity, yet we have discovered a history that staggers even
the imagination itself, and can foresee a future that shall rival
its past.
CHAPTER XXI
IGNEOUS FORCES ON THE MOON AND ELSEWHERE
" He scarce had ceased, when the superior fiend
Was moving toward the shore : his ponderous shield
Ethereal temper, massy, large, and round,
Behind him cast ; the broad circumference
Hung on his shoulders like the Moon, whose orb
Through optic glass the Tuscan artist views
At evening from the top of Fesole',
Or in Val d' Arno, to descry new lands,
Rivers, or mountains, in her spotty globe."
Milton, " Paradise Lost," Bk. I.
BY this time we should have a very fair idea of the construc-
tion, dimensions, distances, and histories of the various
celestial mansions which compose the visible part of the Grand
Temple of the Universe. It is now time to turn nearer home
and find what there is to be seen and learned of the satellite
which is such a faithful attendant on the Third Planet of the
Solar System.
Some details have already been given about our Moon, but
little has been said concerning its present appearance and
condition, or about the changes that have taken place on it
since it left the embrace of its earthly parent. 1
The history of the Moon, like the histories of its ancestors
the Earth, the Solar System, and the Universe is not
recorded in books that were written by eye-witnesses. It has
to be obtained by carefully observing its present appearance
and condition, and then by reasoning as to the way in which
natural laws (known and unknown) can have brought about
1 Since the Moon owes its separate existence to the gravitational attraction of
the Sun on the body of the Earth, it shares with many of the heroes of antiquity
the honour (?) of having a heavenly father and an earthly mother.
244 HOW TO KNOW THE STARRY HEAVENS
that appearance and condition. The most that we can reason-
ably hope for, under these circumstances, is to get a fairly
accurate idea of the main sequence of events without laying
too much stress on minor details. Indeed we must not be
surprised if we find that recognised authorities sometimes differ
with regard to the course of events, as well as to the relative
importance of the different agencies that have been at work
on it. Past experience has shown that incorrect theories will
sooner or later be found out, and replaced by others that are
nearer the truth.
LUNAR FEATURES
If we examine the Moon with the unaided eye, when our
side of it is fully illuminated by the Sun, we can see very little
as to its condition except that it appears to be a tolerably
bright round disc with some irregular dark patches on it.
Each of these dark patches remains permanently in about the
same part of the disc, and has been there since history began.
It is therefore evident that the Moon always turns the same
side to us. The only considerable change is in the direction
from which it is illuminated by the Sun as it revolves around
the circling Earth.
With the help of an opera-glass (also used at full moon),
these lunar patches become very much plainer, and appear to
have a somewhat circular outline. There also comes into
sight a star-like series of bright radiating streaks, having their
centre near the south of the visible disc. These two pecu-
liarities together give the full moon a strong resemblance to a
peeled orange that has been badly bruised. 1
1 If two photographs of the Moon are taken from rather different standpoints,
and then combined so as to be used in the stereoscope, this resemblance to a bruised
orange becomes quite startling. Thus viewed, the Moon loses the flat disc-like
appearance due to its immense distance, and stands out as a solid sphere just as
it would appear to a giant whose eyes were thousands of miles apart. The same
principle has also been applied to planets and comets, so as to show them as they
really are, standing out solidly between us and the more distant background of
stars. Efforts are now being made to get similar stereoscopic pictures of the
stars, by coupling photographs taken at intervals of many years.
FIG. 113. FULL MOON SHOWING RADIATING STREAKS
IGNEOUS FORCES ON THE MOON 245
With a small telescope the whole surface is seen to consist
of solid land like that of our continents. The Moon is there-
fore a solid sphere (or spheroid) like our Earth, but without
any oceans or seas. The dark patches are now recognised to
be tolerably level plains of a darker material than the rest of
the surface. Some of these plains are more or less surrounded
by mountain chains, or lesser elevations.
The telescope also brings into view a large number of smaller
and more regular circles scattered on all parts of the visible
surface. Those, however, which are near the edge of the disc
are distorted into ellipses by perspective. The largest of these
rings are easily seen to consist of a circular embankment or
rampart surrounding a saucer-like depression in the centre of
which there is often an irregular conical elevation.
When the Sun shines obliquely on these circular ramparts,
their shadows are seen extended on the plains beyond, as well
as on the floor of the interior. Where they are numerous the
scene reminds one of a plaster-of-paris surface that has been
filled with bubble-holes by means of citrate of magnesia.
When such a surface is illuminated from one side by a power-
ful electric light, it makes an almost perfect representation of
some parts of the lunar disc.
Those who are acquainted with volcanic districts on our
Earth will have no difficulty in recognising these hollow cir-
cular objects as volcanic craters with or without central lava
cones.
These lunar craters are extremely numerous and vary greatly
in size. The largest are considerably over one hundred miles
across, and below this all sizes are represented down to invisi-
bility, the smallest seen being less than a mile across.
On and near the dark plains these craters are tolerably
plentiful, but toward the southern part of the Moon's disc they
are so astonishingly numerous that they crowd together and
overlap one another. The large ones are often filled with, and
surrounded by, swarms of little ones, which even perch on the
summits and slopes of their ramparts.
246 HOW TO KNOW THE STARRY HEAVENS
Several of the larger craters form centres for bright star-like
radiating streaks extending along the surface for hundreds of
miles. The most extensive set of these has already been men-
tioned as giving the full moon the appearance of a peeled
orange. Its longest streak can be traced for over 2,000 miles.
With a powerful telescope long narrow cracks are also visible
on the Moon's surface, as well as crust foldings and all kinds
of small irregularities which need not be here described. They
are beautifully pictured in Nasmyth and Carpenter's splendid
but expensive work entitled " The Moon."
IGNEOUS FORCES
Now it is evident that most, if not all, of the lunar features
just mentioned are of exclusively igneous or volcanic origin. 1
There is no single feature or peculiarity which can with cer-
tainty be ascribed to either air or water. Oceans, seas, lakes,
marshes, rivers, planes of denudation, snow-patches, ice-sheets,
clouds, mists, and such-like aqueous features and phenomena,
are conspicuous by their total absence.
On our Earth the various aqueous agencies have for millions
of years waged an unceasing conflict with the igneous agencies,
and have now almost won the fight. But on the Moon the
igneous forces have had all the field to themselves, and have
had to deal with a force of gravitation only one sixth as great
as that on our Earth. We therefore find that all the lunar
features are such as would be produced by volcanic forces
working under peculiarly favourable conditions. When com-
pared with similar volcanic features here they are seen to be on
a vastly greater scale, differently proportioned, and more per-
fectly preserved.
Before dealing further with the condition, peculiarities,
origin, and development of these lunar features, it may be well
to say a few words about the various ways in which volcanic
forces are likely to act under widely different conditions. We
1 The word " volcanic " is here used in its widest sense.
IGNEOUS FORCES ON THE MOON 247
shall then be better able to understand the unfamiliar shapes,
sizes, and other peculiarities of the lunar relics of igneous
action.
HOW A MOLTEN WORLD SOLIDIFIES
The cooling off of a luminous gaseous sun or planet, first into
a liquid and then into a solid state, is an exceedingly protracted
process. An appreciable part of it has never been witnessed
by ephemeral man. This being the case, it must be borne in
mind that the following account is almost entirely theoretical.
No one can prove its truth, though the greater part of it is
supported by many forms of indirect evidence. The most that
can be said for it is that it is exceedingly probable.
After a gaseous sun-like world has cooled off sufficiently to
allow its most combustible elements to burn themselves into
chemical compounds, it still continues to cool off by radiation
into space. So in time the bulk of its material leaves the
gaseous state and forms a spherical white-hot molten globe.
This is extremely dense and compressed at the centre, where
the heavier elements and compounds naturally tend, and com-
paratively thin and " watery " near the surface, where the pres-
sure is small. When the molten globe is of any considerable
size it is surrounded by an atmosphere composed of those gases
which liquefy only at a low temperature.
If the world under consideration is only a subordinate centre
of condensation, it still continues to revolve around the main
centre, as in its gaseous youth. Its rotation not only continues,
but (if not counteracted by tidal action) increases in rapidity
as it cools and shrinks. And any tides that may have been
previously produced in it by large neighbouring bodies will
still continue to affect it.
In time the radiation of heat into space will chill, and even-
tually freeze, the surface of the molten world. The time occu-
pied in solidifying will depend on the mass of the cooling world
and on the resulting density of its atmosphere.
The solid outside crust will gradually get thicker, but, if
248 HOW TO KNOW THE STARRY HEAVENS
neighbouring worlds cause any considerable tides beneath, it
will be liable to be fractured as soon as it loses some of its
flexibility. The cooling and freezing processes, however, go
on at the surface without interruption, though considerably
hindered by the more or less violent physical and chemical
reactions below.
At last a tolerably solid crust is formed, covering the entire
world to a considerable depth. This crust is all the time en-
croaching on the molten nucleus inside it, and will eventually
replace it to the very centre.
But before that can take place there will be a terrible struggle
for supremacy between the cooling and crushing shell, and the
crushed and overheated nucleus.
For the laws of cooling and contraction are such that just
before a liquid turns to a solid it swells out and occupies more
room than it did before, and that after it has solidified it shrinks
as it continues to cool off. 1
Owing to these peculiarities the solid outside crust at first
contracts faster than the nucleus inside it. The strain produced
by this cause (assisted by the presence of confined gases) is
tremendous beyond conception, and appalling in its world-wide
effects. When at its greatest intensity it causes the world to
throb and quiver from centre to circumference. The crust frac-
tures and gapes from pole to pole. Near the centres of force
the surface-blocks jump like the lid of a pan full of boiling
water. The molten rock and its confined gases (which consist
partly of the vapour of water) force their way through the
cracks and gaping fissures. Where their escape is strongly op-
posed, they issue in explosive fountains of fiery solids, liquids,
and gases, and bombard the heavens with an incessant and
ear-rending cannonading that defies description. If an eye-
witness could view the stormy scene from a safe distance, he
might think that the throes of Eagnarok were at their height.
1 The freezing of water and solidification of type-metal sufficiently illustrate
the former peculiarity, and the cooling of almost any solid substance exemplifies
the latter.
H
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or THE
UNIVCP.S/TY
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IGNEOUS FORCES ON THE MOON 249
And in fact he would not be far wrong, for the old Norsemen
probably got the germ of that grand conception from the world-
rocking convulsions of the Icelandic volcanoes.
In the course of time the solidifying process gets nearer the
centre of the world. The igneous forces are therefore hampered
by the increasing weight of the solid crust above. The molten
nucleus now contracts faster than the solid crust, and the latter
crumples and folds as it settles down on the outside of it. The
strains produced by both contraction and expansion vary in di-
rection and intensity, and the surface phenomena vary accord-
ingly. The igneous manifestations in time become less violent,
and the conflict gradually dies away into feeble and intermittent
spasms, which at last entirely cease.
The natural features resulting from the above conflict vary
according to the intensity of gravitation, the density of the at-
mosphere, the amount of water above and below the surface,
and such like peculiarities, and these, in their turn, depend
largely on the size of the cooling sphere.
TIME OCCUPIED IN SOLIDIFYING
On a little world, like our Moon, for example, the force of
gravitation is small. Consequently the gases and vapours appear
to leave the planet as they are liberated. It is therefore ex-
posed to the intense cold of outer space, and, as its surface is
large when compared with its mass, it cools off in a compara-
tively short time.
On a somewhat larger world, like the Earth or Venus, gravi-
tation is more powerful, and retains all the gases except the
very lightest. It is therefore surrounded by a dense, foul, and
cloudy atmosphere, which retards and lengthens the cooling
process. But, as soon as the surface temperature is low enough
the aqueous vapour in this atmosphere turns to liquid drops
and rains down on to the solid surface. At first this surface is
too hot to retain the water, and it is driven off again in the
form of steam. But after a time it collects into rivers of hot
250 HOW TO KNOW THE STARRY HEAVENS
water and flows into any depressions there may be in the crust.
There it forms oceans, seas, and lakes, of more or less saline
water. This, by its alternate evaporation and condensation,
produces on the dry land all the well-known phenomena of
aqueous denudation.
On a still larger world, like Saturn or Jupiter, the process is
still more hampered and prolonged by the intensity of gravita-
tion and by the extent and density of the cloud-packed atmos-
phere. 1
In the case of huge bodies like our Sun, and of still larger
ones like Canopus and Rigel, the time taken to cool off (first to
a liquid, and then to a solid state) is so enormous that it is
beyond the comprehension of ephemeral beings. Reason may
be able to estimate the period in years, but even the imagination
fails to grasp and realise its vastness.
COMPARATIVE EFFECTS OF IGNEOUS FORCES
When this conflict was at its height on our Earth, the cen-
tral attraction of gravitation was (as now) considerable when
compared with that of the Moon, and there was a dense acrid
atmosphere all around, which at first contained all the water
now in the oceans. These features would act as a check on
the igneous forces, prolong tbeir action, and make their per-
manent records less conspicuous. Yet geology shows that some
tremendous results were produced even when the conflict was
dying away.
Leaving the more ancient and important effects out of con-
sideration, the crater of Haleakala, which has an area of 16
square miles, is an awe-inspiring evidence of past volcanic
1 The low density of the large outer planets shows that they are still in a
gaseous state with possibly a small molten nucleus. Owing to their rapid rotation
the dense clouds by which they are surrounded are whirled into more or less per-
manent latitudinal belts, which compose the only visible part of the planet. The
belts on each side of the Equator exhibit more frequent changes than elsewhere.
The Sun has a somewhat similar peculiarity, as the sun-spots and eruptive promi-
nences are mainly confined to the same " sub-tropical " regions.
IGNEOUS FORCES ON THE MOON 251
power. The eruption of Krakatoa, a few years ago, shook the
Earth to its very centre and from pole to pole. Its upward
cannonading was so terrific that it was heard 3,000 miles away,
and it almost shot its projectiles into outer space. The Japan-
ese earthquakes, even now, are active enough to cause the
islands to be facetiously termed " The Lid of Sheol." Even the
sputterings of Mont Pele'e and Vesuvius are sometimes violent
enough to inspire our respect. Who, then, can describe, or
even imagine, the world-wrecking violence of the igneous forces
when they were at the height of their strength and activity,
before geology began ?
On a much larger world than ours, with heavier rocks and a
still denser atmosphere, the igneous forces are even more
cramped than here, and the radiating surface is smaller in com-
parison with the mass. The process, therefore, continues for a
much longer time, and the resulting evidences are compar-
atively insignificant.
FIG. 115. SECTION OF EARTHLY VOLCANOES
Built up of ashes and cinders, with interstratified lava streams.
But on a smaller world, like our Moon, the igneous forces
appear to be practically unfettered. As the material there is
only one sixth as heavy as it would be on our globe, it can be
moved with only one sixth the effort.
If two volcanoes, one on the Moon and the other on the
Earth, were each to eject the same kind of material with the
same amount of force and under the same atmospheric condi-
tions, the lunar projectiles would go six times as far as the
earthly ones. But as there is no resisting atmosphere on the
Moon, the lunar volcano will scatter its debris to an even
greater distance than the difference in weight would indicate.
HOW TO KNOW THE STARRY HEAVENS
The result is that a violent, explosive, and long-continued
eruption will not (as here) build up a huge mountain of debris
with a small crater on its summit. It will tear out an enor-
mous circular funnel-shaped hollow, surrounded by a massive
rampart just at the edge of the volcano's field of force.
FIG. 116. SECTION OF LUNAR VOLCANO IN FULL ACTIVITY
It may be well to give one or two illustrations of these dif-
ferences in size and proportion between the earthly and the
lunar volcanoes.
The largest volcanic crater on our globe is an extinct one in
the Hawaiian Islands, that goes by the musical name of Hal-
eakala. Its size, however, has been increased and its shape
altered by an explosion like that which blew the head off the
original Mount Vesuvius. The crater as it now exists is 7^
miles across, one way, and 2i miles the other. It has an area
of about 16 square miles, and the depth is about 2,700 feet.
There are 16 conical hills scattered about its interior, from 500 to
600 feet in height. It is perched on the summit of a mountain
20 miles across and 10,000 feet above the sea-level.
In the southern part of the Moon is a crater to which has
FIG. 117. CLAVIUS AND TYCHO
The former is the large walled plain near the bottom of the picture. The latter is the
centre crater. It is the source of the chief lunar radiating streaks, which are
only visible at full moon. Photographed at Yerkes Observatory.
T\B R ATT?*
CK THE
UNIVERSITY
or
*Li
IGNEOUS FORCES ON THE MOON 253
been given the name of Clavius. It is one of the largest on our
side of the Moon, and has several smaller and more recent
craters scattered about its interior. It is more than 140 miles
across, and has an area of about 16,000 square miles. Its ram-
part in some places reaches a height of 17,000 feet above the
inside floor, which is about two miles below the level of the
outside plain.
This crater, like all the very large ones on our side of the
MOOD, has no central cone. It is thought by some that these
coneless craters are not the result of explosive volcanic erup-
tions, but that they were formed as seething lakes of molten
lava, like the crater of Kilauea in the Hawaiian Islands.
There are many, however, which have inside cones, indicating
that they are true volcanic craters. It may be as well to give
the dimensions of one of the largest of these.
Theophilus, one of the most perfect craters on the Moon, is
64 miles across, and has an area of about 3,200 square miles.
Some of the peaks on its rampart reach an elevation of 18,000
feet above the floor of the crater. One of the cone-shaped
mountains in its centre is 6,000 feet high, yet its summit is
4,000 feet below the level of the outside plain. A number of
similar craters are scattered around, but they are smaller or in
a less perfect state of preservation. Besides these, there are
swarms of craters so small that only a very powerful telescope will
show them. But, small as they are, they are equal in size to the
craters of the largest earthly volcanoes.
VARIETIES OF IGNEOUS ACTION
The solid crust which first forms on a solidifying world is
more or less flexible on account of its thinness and high tem-
perature. As it cools off and loses this flexibility it is cracked
in all directions by the tides and other strains to which it is
exposed. The cracks are filled up with molten rock, which
sometimes reaches the surface and spreads over it in thin
sheets. As this liquid matter cools and consolidates, it cements
the crust solidly together again. The process goes on till the
254 HOW TO KNOW THE STARRY HEAVENS
whole shell is traversed in every direction with dykes and
veins of mineral matter.
When the crust has become thicker, and the interior strains
are greater, the molten matter exudes in greater volume from
FIG. 119. SECTION OF MOUNTAIN OF EXUDATION
the cracks. It solidifies quickly on the cold surface, and piles
itself up in great heaps, forming ridges and sometimes moun-
tains of exudation. The action is something like that of our
mud- volcanoes, only the material is plastic through heat instead
of water.
In time the molten nucleus becomes small, in proportion to
the outside shell. It then contracts faster than the crust, and
leaves the latter to fold and shrink upon it like the skin of a
FIG. 120. SECTION OF MOUNTAIN OF ELEVATION
wizened apple. This folding or crumpling produces what are
known as mountains of elevation , consisting of more or less
parallel ranges of folded rock. 1
The molten matter, instead of exuding quietly up wide cracks
to the surface, and there cooling off on the mountain slopes, is
1 The character, distribution, and condition of these folded rocks will depend
upon whether or not the world has a permanent atmosphere and a large amount
of water on its surface. Also on whether it has any external source of heat and
light, to keep those agencies in a state of activity.
V 1 J f '
feV$i&'i
s i Y- .
FIG. 118. THEOPHILUS, A LUNAR CRATER-WITH-CONK
64 miles across. Yerkes photograph.
IGNEOUS FORCES ON THE MOON 255
now forcibly ejected from a series of blow-holes along the
closed or choked cracks. 1 The result is that instead of piling
up mountains of exudation it forms volcanoes of eruption.
The funnel-shaped hollow or crater formed at the top of one
of these blow-holes is surrounded by a rampart composed of
the ejected material. While the explosive force is increas-
ing, the hollow gets larger, and the rampart is pushed farther
back. The size of the crater is therefore a measure of the energy
of the volcano at the height of its power, during its most
violent paroxysms.
When the explosive force abates somewhat, small craters are
formed inside the large one. When the violent eruptions give
way to a quiet yet considerable oozing of molten rock, it fills
up the crater till the rampart gives way, and then floods the
surrounding country with more or less liquid lava. When there
is not enough lava to overflow the crater, it simply solidifies
inside, forming a nearly level floor. And when the lava flow is
FIG. 121. SECTION OF LUNAR CRATER WITH CONE
too small or viscid to spread over the crater, it solidifies into
conical peaks above the central vent.
Sometimes a volcano becomes inactive, not because the energy
is exhausted, but because it is intermittent and the vent has
become plugged up during a quiet interval. A subsequent dis-
turbance, if powerful enough, will either blow out the obstruc-
tion or force a vent in some other part of the line of weakness.
In the latter case the crust will be fractured afresh, and other
1 The violence of its action depends largely on the quantity of water which
gets to the hot interior, and on the volume and character of the gases produced
by chemical action.
256 HOW TO KNOW THE STARRY HEAVENS
craters will be formed. The old one will then remain dormant
or become extinct.
As the volcanic forces become exhausted, the craters formed
are, of course, smaller than the old ones. And so at last the
igneous action ceases to be visible on the surface of the now
solid world.
The subsequent history of the world in question will depend
upon the presence or absence of air and water in a state of
activity. With them, the surface structures reared by igneous
action will be gradually obliterated. Without them, the only
changes will be landslides due to variations of temperature act-
ing on the piled-up crater ramparts and precipitous mountain
slopes. With this exception the volcanic structures will be
perfectly preserved for as many millions of years as the petrified
world containing them continues to have a separate existence.
CHAPTER XXII
LUNAR GEOLOGY AND GEOGRAPHY
" Speaking by our own lights, from our own experience and reasoning, we are
disposed to conclude that in all visible aspects the lunar surface is unchangeable ;
that in fact it arrived at its terminal condition eons of ages ago ; and that in the
survey of its wonderful features, even in the smallest details, we are presented
with the sight of objects of such transcendent antiquity as to render the oldest
geological features of the Earth modern by comparison." Nasmyth and Car-
penter, " The Moon."
BIRTH OF THE MOON
WHEN the Moon still formed part of the Earth, the whole
mass was probably in a molten condition, and surrounded
by an extremely dense atmosphere which contained all the
water now in the oceans, seas, and lakes. The atmospheric
pressure must then have been equal to about 5,000 pounds to
the square inch.
Owing to the rapid and increasing rotation the molten body
was very much spread out at the equator, and the atmosphere
was deeper and denser there than near the poles. The loss of
internal heat by radiation was therefore greatest at and near the
poles. This probably led to great convectional currents in the
molten globe. The same cause led to atmospheric currents
the lowest of which were from the northeast to the southwest
in the northern hemisphere, and vice versa in the southern.
The attraction of the Sun, acting on the molten rock of which
the rotating spheroid consisted, presumably raised a huge and
ever-increasing tide on the side nearest to it. As the rotation
quickened, this solar tidal wave of molten rock grew in size
until it was finally thrown off and became the Moon, as de-
scribed in a previous chapter.
17
258 HOW TO KNOW THE STARRY HEAVENS
Now the material which went to form the Moon was not
taken from the heavy central metallic rock (8.2), but from the
lighter envelope of molten silicates, with a density of a little
over three times that of water (3.2). And the heavy atmos-
phere of steam and other gases was either retained or drawn
back by the Earth on account of its superior size and attraction.
The lunar silicates, however, were probably heavily charged
with steam, etc., owing to the enormous atmospheric pressure to
which they had previously been subjected.
The orbit of the new-born Moon gradually increased in size,
from the tidal action. The molten silicates composing the
Moon, being relieved from the tremendous atmospheric pressure,
gradually expelled the steam and gases with which they were
charged. They thus formed a huge globe of "boiling" rock,
which cooled off on every side, by radiation into space, until
the surface matter solidified.
THE GREAT PLAINS
The escaping gases, assisted by the earth-tides, probably
broke up the first crust, and the fragments floated and drifted
on the still molten surface. Large open lakes of boiling rock
may thus have been left between them. These molten lakes
would be something like that in the crater of Kilauea, but of
vastly greater dimensions. They were sometimes many hun-
dreds of miles across, and were more or less surrounded by
rocky ramparts. These may have been built up of solid blocks
driven to the sides by the violent ebullition and diverging
surface currents.
In the course of time these hypothetical molten lakes cooled
off and solidified. They form the dark level plains visible from
the Earth with the naked eye. Before the invention of the
telescope they were thought to be seas ; and the Latin name
for a sea has stuck to them ever since. 1
1 Even Kepler shared in this erroneous belief. In one place he says "Do
maculas esse maria, do lucidas esse terras." Galileo, on the contrary, appears to
have discovered that there are no visible bodies of water on our side of the Moon,
3 1
LUNAR GEOLOGY AND GEOGRAPHY 259
Most of these great plains have either a circular outline or
are more or less surrounded by semicircular bays. Mare
Serenetatis (the Sea of Serenity) is an example of the former,
and Mare Imbrium (Sea of Showers) of the latter. This
circular feature is not the result of accident. Whatever differ-
ences of opinion there may be as to the way in which they
originated, it is certain that they are the result of (igneous or
other) forces acting from local centres.
THE WALLED PLAINS
Mare Crisium, one of the smallest and most regular of the
great plains, connects them with the crater-like watted plains,
of which the best examples are known by the names of Ptolemy,
G-rimaldiy Clavius, Schiller, and Schickard. Most of these are
over 100 miles in diameter.
In spite of the enormous -surface dimensions of these walled
plains, and of the fact that they have a practically level floor
with no central cone, their appearance is so crater-like that it is
impossible to draw a satisfactory dividing-line between them
and the smaller volcanic craters which were subsequently
formed. Their resemblance is so marked that it is evidently
due to relationship.
RADIATING STREAKS
After the surface had cooled off and consolidated, the cooling
process went on below, adding to the solid crust at the expense
of the molten nucleus. The varying ratios of contraction, etc.,
gave rise to violent strains which resulted in immense cracks
radiating in all directions from the local centres of force. The
molten lava welled up through the cracks and spread over the
for his friend Milton carefully avoided mentioning lunar oceans and seas. He
made Raphael watch the Earth
" as when by night the glass
Of Galileo, less assured, observes
Imagined lands and regions in the Moon."
" Paradise Lost," Bk. V.
260 HOW TO KNOW THE STARRY HEAVENS
surface for some little distance in thin watery sheets. These
of course soon solidified, and are now visible when the Moon is
at its full.
MOUNTAINS OF EXUDATION
At a later time, when the conditions were rather different,
the solid crust appears to have been again fractured in some
parts of the Moon, and immense quantities of molten lava
welled out onto the surface. There it cooled off and solidified,
like spring water that comes to the surface in a severe frost.
In this way long ridges of solidified lava were formed, with
open vents all along the summit. Through these vents the
quiet exudation of lava continued until the ridges became
mighty ranges of mountains. Such are the Leibnitz Mountains,
in the extreme south of the Moon. These have an elevation
of 31,000 feet above the general surface. They are therefore
higher in proportion than any mountains on the Earth.
Another important range is known as the Lunar Apennines,
a little to the north of the centre of our, side of the Moon.
It is an extremely wild and precipitous range of mountains
about 480 miles long and of considerable width. It contains
about 3,000 peaks, which probably represent the widest parts
of the elongated cracks through which the liquid silicates rose
to the surface. Some of these summits are 18,000 feet above
the level of the plains below.
The Caucasus Range and the Lunar Alps are similar
mountains of exudation. The latter range contains 700 peaks
and is almost cut in two by a remarkable straight valley with
a level floor and precipitous sides 11,000 feet high. It is 80
miles long and about 5 miles wide at the bottom.
With perhaps the exception of the first mentioned, all these
ranges of mountains have a steep precipitous slope toward the
Moon's west, 1 and a long gradual slope on the side toward
which they are carried by the Moon's rotation. In this respect
they resemble the Andes of South America.
1 Toward the east as seen from the Earth.
liili
:fi'l
m -
!OTs
MmMM
FIG. 124. COPERNICUS
By Nasniyth and Carpenter. (From " The Moon," by Nasmyth and Carpenter,
published by John Murray. )
LUNAR GEOLOGY AND GEOGRAPHY 261
ISOLATED PEAKS
A few isolated peaks were also formed, perhaps by the same
quiet exudation of rather viscid lava. They rise rather abruptly
from the level plain, like some vast cathedral. There is one in
the north which goes by the name of Pico. It rises almost
precipitously to a height of 8,000 feet. 1
EXPLOSIVE VOLCANIC ERUPTIONS
After these mountain ranges and isolated peaks had been
more or less quietly formed on the northern plains the increas-
ing shrinkage of the nucleus appears to have closed up the
wide cracks and made egress to the surface more difficult.
The result was that the volcanic forces became violent, and the
molten lava, instead of quietly oozing up all along the cracks,
was forced up explosively at distant centres. Owing to the feeble
gravitation, and to the absence of atmospheric pressure, the
resulting volcanic craters were so tremendous in size that we
have nothing on Earth anywhere approaching them.
After the volcanic forces had passed their maximum the
large craters were choked up, and smaller ones were formed on
their flanks, to be in time superseded by still smaller ones.
There are sometimes strings of them, evidently formed along
the same crust-fractures.
QUIET VOLCANIC EXUDATIONS
The explosive volcanic eruptions were sometimes succeeded
by the quiet exudation of lava through the same volcanic vents.
Where the flow was very abundant the crater was filled till the
lava broke down the rampart and flooded the outside plains.
In the case of one crater, which has been named Wargentin,
the lava rose to the very brim of the crater and there solidified,
forming a round table-mountain 53 miles across.
1 The lunar peaks are not really as precipitous as one would think from the
long shadows they causet
HOW TO KNOW THE STARRY HEAVENS
In cases where the flow of lava was less abundant the craters
were partly filled up, and have now either a level or a slightly
convex floor. 1 Very often this has a number of little craters
scattered about it, and has also a cone, or series of cones, over
the central vent.
As no two of the lunar craters were formed under exactly
the same conditions, it is not surprising to find that each one
has an individuality of its own. Yet if we except the great
differences in size, which are easily explained, it will be found
that their resemblances are much more marked than their
differences. There is not the shadow of a doubt as to their
volcanic origin, and geologists can learn many a lesson as to
the history of the Earth by studying the volcanoes on the
Moon.
OPEN CRACKS
After all volcanic activity had died away on the Moon's sur-
face (and probably after the Moon had solidified to its centre),
large numbers of surface cracks were formed by the continued
contraction. Many of them are of such a tremendous size that
they are visible to our telescopes. Some can be traced for
more than a hundred miles, being from one to two miles wide
and of great but unknown depth.
These open cracks in some cases cut clear through the
previously formed craters. Not only are some of the large
and early craters thus intersected, but also some of the small
and more recent ones.
With the formation of these open cracks the Moon's activity
apparently ceased and it became what it is to-day and what
our Earth will be to-morrow a dead world.
TYPICAL FEATURES
The study of lunar geology leads naturally to lunar geography,
which is its product. The principal features can be best learned
with the help of a good telescope, assisted, and preceded, by
1 Due to imperfect fluidity.
t>' * iio
x *u *) . i:
*
as
FlO. 125. SCHICKAUD AND WARGENTIN
By Nasmyth and Carpenter. (From " The Moon," by Nasmyth and Carpenter,
published by John Murray.)
LUNAR GEOLOGY AND GEOGRAPHY 263
the study of lunar charts and photographs. It may he well,
however, to point out some of the best illustrations of the
peculiarities already mentioned.
The G-reat Plains are conspicuous objects on account of
their great size and dark hue. Most of them can be made out
with an opera glass, or even with the naked eye. Their names
will be found on the lunar charts at the end of the book.
The bright streaks which have been mentioned radiate from
the craters which bear the celebrated names of Tycho, Coper-
nicus, Aristarchus, Kepler, and Proclus. These craters de-
veloped after the streaks were formed, but owe their positions
to the weakness and open state of the crust at the centre of
fracture.
There are over 100 streaks radiating from Tycho. They
spread over a great part of the Moon's surface. One of them
passes under the distant crater Menelaus, stretches clear across
the " Sea of Serenity," and is finally lost to sight at the north-
ern edge of the Moon.
The streaks radiating from Copernicus are next in importance.
They are so intricate as to be uncountable.
The Aristarchus streaks appear to have been formed after
those of Copernicus but before those of Kepler.
The craters-with-cones vary in size from the giant Petavius,
78 miles across, to the little companion to Hell, 1-f miles in
diameter. There are probably many smaller ones which the
telescope fails to reveal.
Copernicus, 56 miles across, is one of the grandest objects on
our side of the Moon. It is remarkable not only for its radiat-
ing streaks, but also for the landslides on both sides of its
rampart, for its radial spurs extending for 100 miles, for the
open cracks in its neighbourhood, and for the thousands of tiny
craters which surround it.
Plato, 60 miles across, is a coneless crater easily recognised,
at full moon, as a dark oval spot near the northern edge.
Like all other craters, it is better seen when the sunshine falls
on it at an angle, and throws the black shadows of its sur-
264 HOW TO KNOW THE STARRY HEAVENS
rounding peaks on the smooth inside floor and on the hill
country beyond. It has a considerable landslide on the inner
side of its rampart, and there are thirty very small craters
scattered about on its level floor. The Lunar Alps are close by,
cut hi two by the curious straight valley already mentioned.
Aristarchus, 28 miles across, is as easily recognised by its
brilliant chalk-like hue, that almost dazzles the eye. The sur-
face outside appears to be folded into parallel ridges, and there
is a curiously contorted crack, not far away, which is about two
miles in width.
Ptolemy, Alphons, and Arzacha,el, near the centre of ou~
side of the Moon, form one end of a more or less continuoui
chain of large craters extending to the south. Near the last
named is a huge circle with a scarcely perceptible rampart.
Across this almost smooth circle there runs what looks like a
straight railroad embankment, about 60 miles long and 2,000
feet high. From its artificial appearance it is commonly known
as The Railway.
Every part of the Moon's surface is full of objects that are
interesting when seen through a good telescope with the right
illumination. With the exception of the bright streaks, all the
lunar features are best observed when they are near the chang-
ing " terminator," so that the light falls on them at an acute
angle.
FIG. 126. PTOLEMY, ALPHONS, AND ARZACHEL
By Nasmyth and Carpenter. (From " The Moon," by Nasmyth and Carpenter,
published by John Murray.)
CHAPTER XXIII
INHABITED WORLDS
" As there are other globes like our Earth, so there are other [family groups]
like our Solar System. There are self-luminous suns exceeding in number all
computation. The dimensions of this Earth pass into nothingness in comparison
with the dimensions of the Solar System, and that system, in its turn, is only an
invisible point if placed in relation with the countless hosts of other systems.
Our Solar System, far from being alone in the Universe, is only one of an exten-
sive brotherhood, bound by common laws and subject to like influences. Even in
the very verge of creation, where imagination might lay the beginning of the
realms of Chaos, we see unbounded proofs of order, a regularity in the arrange-
ment of inanimate things, suggesting to us that there are other intellectual
creatures like us, the tenants of those islands in the abysses of space." Dr. J. W.
Draper.
ARE OTHER WORLDS INHABITED?
IN ancient times our Earth was supposed to be the only world
in existence. In fact the Universe was thought to consist
solely of our Earth and its appendages. But in the course of
time it was discovered that the Earth is only one member of a
family of worlds, and that there are other families of worlds
outside of our own.
These two discoveries naturally gave rise to a lively discus-
sion as to whether those worlds are, as a rule, inhabited by
living organisms.
At first, pride and theological prejudice led many people to
deny emphatically the existence of any kind of life on other
worlds. Even after the consideration of probabilities had led
to the abandonment of this position, the existence of rational
life was strongly contested.
After this came a time when the most progressive minds
went to the other extreme. They claimed that life probably
266 HOW TO KNOW THE STARRY HEAVENS
exists on every world of any size, at a certain stage in its
development.
The first of these extreme views concerning the plurality of
worlds has long been abandoned by all intelligent and well-
informed persons. The last is now being somewhat modified
by astronomers. They consider that, while it is absurd to sup-
pose that our Earth is the only inhabited world in the Universe,
the opposite extreme is not supported by the available evidence
as to the conditions existing on other worlds.
While the extreme affirmative side was in the ascendency,
certain imaginative astronomers (and other imaginative persons
who were not astronomers) stated that they had recognised
indications of life on the Moon. A little later, some of our
very best observers constructed charts of Mars showing the
dark markings on it connected together by very artificial-looking
" cobwebs." Schiaparelli gave the Italian name canali (mean-
ing " channels " ) to these elusive markings. English-speaking
people mistook the Italian canali for the. English word " canals,"
and jumped to the conclusion that Mars is inhabited by very
enterprising engineers who eke out a small water-supply by
means of large irrigating canals. The theory was afterward
made less absurd by the supposition that the markings were
not the canals themselves, but the belt of vegetation on each
side of the main ditch.
Made enthusiastic by this supposed identification, one or two
sensational astronomers went a step farther, and asserted that
the Martians were trying to attract our attention by displaying
geometrical signals constructed on a world-wide scale.
The supposed evidences of life on the Moon were easily
proved to be wholly imaginative. In one rather notorious case,
indeed, they turned out to be nothing but a hoax, gotten up to
test the credulity of the general public.
With regard to the " canals " of Mars, the belief is now grow-
ing stronger among astronomers that they are largely subjective
phenomena that in fact the majority of them are optical
delusions caused by the observers over-straining their eyes in
INHABITED WORLDS 267
the effort to make the best use of their telescopes. The rest of
them are probably due to close sequences of spots too faint to
be separately visible.
The truth appears to be that our optical appliances, powerful
as they may be, are yet very far from the degree of perfection
required in order to detect evidences of life in other worlds.
The probability is that they always will be unequal to the task.
We have therefore no means of actually proving or disproving
the theory that other worlds are inhabited. There appears to
be some positive evidence that the Earth is inhabited, and that
its Moon is not. But apart from these two planets we have no
actual positive evidence that life exists, or does not exist, any-
where in the Universe. And we never shall have.
This being the case, about the only way we can deal with
the problem is to try to find out the conditions necessary for
life as we know it, and to see whether those conditions exist on
any of the other planets hi our System. We shall then be in a
better position for speculating on the probability, or otherwise,
of these worlds being inhabited by living organisms allied to
those on our Earth.
When that question is disposed of, there will still remain
the more obscure problem whether any of the worlds are
tenanted by entirely different forms of life.
ESSENTIALS TO LIFE AS WE KNOW IT
Among the things which are absolutely essential to organic
life here are the four elements known as carbon, hydrogen,
nitrogen, and oxygen.
Of these, oxygen, in a free gaseous state, is essential to all
forms of animal life.
Carbon and oxygen, in combination, form carbon-dioxide
(C0 2 ), which, as a gas, is equally essential to all forms of
vegetable life.
Hydrogen and oxygen combine to form water (H 2 0), which
both plants and animals require in a liquid state.
268 HOW TO KNOW THE STARRY HEAVENS
Carbon and hydrogen form the basis of numerous compounds
which, by their formation and oxidation, alternately accumulate
energy and expend it in motion, etc. These two processes are
together known by the name of energy-traffic.
Nitrogen is necessary, in a free gaseous state, to keep in
check the all-devouring energy of free oxygen. It is also neces-
sary, in combination with the hydrocarbons, to regulate and
control their energy-traffic. It is specially adapted for this
office on account of its sensitiveness to changes of energy and
the resulting instability of its compounds.
All the life on our globe is based on protoplasm, which con-
sists of these four elements. A number of other elements
occur in most forms of life, but do not seem to be so essential
to it.
An intermittent supply of radiant energy also appears to be
necessary to life as we know it. The plants derive their
energy, either directly or indirectly, from the Sun, and the
animals get it at second-hand, from the plants.
The energy-traffic mentioned above can only be carried on
within a certain range of temperature. Life based on proto-
plasm cannot exist where the temperature is permanently
above 150 K, or below 32 F. High temperatures break up
the protoplasm into less complex compounds. Low temper-
atures check and eventually put a stop to its activity.
A certain intensity of the force of gravitation also seems to
be essential to life as we know it. For worlds which are very
much smaller than ours do not appear to be able to retain the
vapours and gases necessary to living organisms, and on worlds
that are very much larger, the same organisms would be
crushed to death by their own weight.
DO LIFE-ESSENTIALS EXIST ON OTHER WORLDS?
When we examine the other planets in our System, we find
that some of these essentials are lacking in every one, and
always will be lacking.
Fastigium Ceryor
30 Margaritifer-Sinus
60 Ganges
90 Solis Lasus
120 Nodus Gordii
150 Mare Sirenum
FIG. 127. TWELVE VIEWS OF MARS
By Lowell. (From Todd's " Stars and Telescopes," published by
Messrs. Little, Brown, & Co.)
180 Atlantis
210 Trivium Charontis
300 Syrtis Major 330 Phisoner Euphrates
FIG. 127. TWELVE VIEWS OF MARS
By Lowell. (From Todd's "Stars and Telescopes," published by
Messrs. Little, Brown, & Co.)
f\BR ATTp
Of THE
UNIVERSITY
or
INHABITED WORLDS 269
Our nearest neighbour, the Moon, shows no signs of having
either air or water. This is probably due to the fact that it is
unable to retain them, except in a solid state. Owing to their
absence, and to the slowness of the planet's rotation, the range
of temperature is too great for any form of life based on the
carbon compounds.
Mercury and Mars probably have a very scanty supply of
both air and water. There are no perceptible oceans or seas on
Mars, and Dr. Campbell, of Lick Observatory, has shown that
the atmospheric pressure on its surface is very small. It ap-
pears, in fact, to be less than that at the summit of Mount
Everest, the highest mountain on our globe. This being the
case, it is possible that the planet is unable to retain the vapour
of water, and that its " snowy poles " are nothing but frozen
carbon-dioxide (C0 2 ), an inch or two in thickness.
Venus probably has a good supply of both air and water.
But as it appears to keep one side always turned to the Sun, it
has not the intermittent supply of radiant energy which is nec-
essary for life on our globe. The Sunward side must be too
hot for protoplasm to exist, and the dark side must be cold
enough to freeze both water and air. Mercury also appears to
possess the same unfavourable coincidence between its rotation
and revolution.
The Asteroids receive much less light and heat than the
Earth. They have probably neither air nor water, as their
gravitation is too small to prevent these from escaping into
space, as free hydrogen does from our Earth.
Jupiter may be said to be all atmosphere, as it appears to be
still in a hot gaseous state, surrounded by thick cloudy conden-
sations. The intensity of the Sun's light and heat is 27 times
less there than on our Earth. Its five moons must therefore
appear as mere wandering stars.
Saturn is not as dense even as Jupiter. And it is still less
favourably situated as regards solar radiation, in spite of its
enormous satellite-rings and numerous moons. For the intensity
of solar light and heat is 90 times less than here.
270 HOW TO KNOW THE STARRY HEAVENS
Uranus and Neptune are little more, at present, than huge
masses of rotating gas, slowly revolving in the gloomy outskirts
of the Solar System. The intensity of Neptune's sunshine
is 900 times less than that which we enjoy. Its lot would
therefore be a cold one if it were not for its store of internal
heat, continually replenished by the gradual contraction of the
planet.
This concludes our survey of the Solar System in search of
the essentials of life. If we wait until the outer planets have
reached the present stage of the Earth, we shall still find the
conditions utterly unfavourable to life as we know it. For the
force of gravitation will still be tremendously greater than
here, and the radiant energy from the distant and waning Sun
will then be insufficient to keep the otherwise dense atmos-
pheres from settling down over their entire surfaces, in a solid
mass of never-melting " snow."
We have then good reason to think that in our own System
the Earth is the only planet on which the conditions are
favourable for life as we know it. That is to say, if life must
necessarily be based on protoplasmic combinations of oxygen,
hydrogen, nitrogen, and carbon, the other planets in our System
appear to be uninhabitable.
Among the many millions of solar systems which surround
our own, it may be regarded as certain that there is no single
world where the conditions sue identical with those on Earth.
But it is possible that there may be quite a number of worlds
where the conditions are somewhat similar to those found
here.
In such worlds we should probably find living organisms
based on the same four elements, but developing along some-
what different lines. For earthly forms of life have grown up
under certain conditions, and cannot exist where those condi-
tions do not prevail. On other planets life would start under
different conditions and develop accordingly. In other words,
the various forms of life on our globe are the result of general
laws operating under special conditions, and the same general
INHABITED WORLDS
laws would, under different conditions, result in different forms
of life.
But although the number of such worlds in the Universe may
be numerically large, it must be relatively small. We know
that the Universe contains hundreds of millions of luminous
suns, and we have reason to believe that they are many times
outnumbered by dark planetary worlds. Let us deduct from
these latter the comparatively small number on which the con-
ditions are presumably somewhat similar to those on our Earth.
The question now remains whether the rest are entirely with-
out life of any kind, or whether they are tenanted by forms of
life which are based on other elements and require altogether
different conditions.
For my part, I must say that the latter seems the most rea-
sonable supposition, considering the resourcefulness of Nature
in our part of the Universe. Yet we have reason to believe
that even our World is entirely uninhabited, except on the thin
surface layer. And it is only habitable there for a compara-
tively snort time. Nature may be as wasteful of worlds as it
is of sunshine.
The fact is that we none of us know anything at all about
this last question. And we never shall know.
WHERE IS THE EARTH?
" Beelzebub. ' There is a place
(If ancient and prophetic fame in heaven
Err not), another world, the happy seat
Of some new race, called Man.
Thither let us bend all our thoughts, to learn
What creatures there inhabit, of what mould
Or substance, how endued, and what their power.'
Satan. ' Whom shall we send
In search of this new world? Whom shall we find
Sufficient? Who shall tempt with wandering feet
The dark, unbottomed, infinite abyss,
And through the palpable obscure find out
His uncouth way, or spread his aery flight
HOW TO KNOW THE STARRY HEAVENS
Upborne with indefatigable wings,
Over the vast abrupt, ere he arrive
The happy isle?
I abroad
Through all the coasts of dark destruction seek
Deliverance for us all : this enterprise
None shall partake with me.'" Milton, "Paradise Lost," Bk. II.
So far the entire subject of inhabited worlds has been treated
from an earthly standpoint. It may be an advantage to con-
sider it briefly from the outside.
Let us suppose for a moment that our Earth is the only
world in the Universe which is inhabited by living organisms.
And let us suppose that from some distant spirit-land a flying
messenger is sent to hunt up our World, without any special
instructions for finding it. Let us also suppose that he can
travel through space at a speed equal to that of light. He may
travel from star to star, for hundreds, thousands, and millions
of years, without being able to find it. " If in the course of time
he comes to our System, he may see the larger and more showy
planets, and yet fail to notice our little World.
If it were to be pointed out to him as the specially favoured
world, he would hardly be able to convince himself of the fact
without a close examination. For the only unusual feature
about it, as seen from a distance, would be that it was attended
by a satellite which was large in proportion to its primary.
Apart from this peculiarity, which may be common in other
systems, the Earth would seem to be merely an insignificant
attendant on a star which was itself almost indistinguishable
from millions of other stars.
That our Earth is the only inhabited world is therefore an
extremely unlikely supposition to be entertained by anyone
who is at all conversant with the dimensions, construction, and
duration of the Universe. It appears reasonable only to one
who is almost entirely ignorant of all except his immediate
surroundings.
Yet there are people on our Earth (even in so-called enlight-
INHABITED WORLDS 273
ened and civilised countries) who not only think that it was
created expressly for the use of man, but also believe that the
entire Universe visible and invisible was made for his
service and edification ! There are persons who actually believe
that the Sun was made to rule an earthly day, the Moon to
adorn an earthly night, the planets to serve as oracles of earthly
fortunes, and the stars to relieve the monotony of an earthly
sky ! The sciences of astronomy and geology show that
natural as these ideas may seem to unenlightened people
they are as baseless as the airy fabrics of a midnight dream.
SUMMARY
Dr. F. J. Allen, in a recent article in the " Popular Science
Monthly," l has ably summed up the argument as to " Life in
Other Worlds." He says :
" 1. If life is essentially a function of the elements nitrogen, oxy-
gen, carbon, and hydrogen, acting together, then it can probably
occur only on exceptional worlds, with conditions closely resembling
those of our own Earth. Such conditions are not present in any
other world in our own Solar System, nor can they be expected to
occur frequently in members of other systems.
" 2. On the other hand, if different conditions can awaken a capac-
ity for exalted energy-traffic among other elements than those just
named, then the Universe seems to provide immense possibilities of
life, whose variety and magnificence may far exceed anything that we
can imagine."
OTHER-WORLD SPECULATIONS
I think that it has now been satisfactorily shown that we
have no direct knowledge whatsoever concerning inhabited
worlds outside of our own, and that we are never likely to
obtain such knowledge.
But on the other hand it has also been shown that it would
be preposterous to suppose our Earth to be the only inhabited
1 November, 1903.
18
274 HOW TO KNOW THE STARRY HEAVENS
world in the Universe. As a matter of probability, we may
safely take it for granted that there are, at the present time,
myriads of inhabited worlds, a certain percentage of which
have developed reasoning beings. We may also take it for
granted that there have been myriads of such worlds in the
limitless past, and will be in the limitless future.
This being so, the question naturally arises, is the life on
those worlds likely to develop along the same lines as here,
or has each world its own special line of development, not con-
ceivable by the inhabitants of any other planet ? In other
words, is it probable that a visitor to one of those worlds would
there find two ascending series of organisms, the one culmi-
nating in flowering shrubs and trees, and the other in back-
boned quadrupeds, headed and more or less controlled by
a reasoning biped like man ?
At first sight it does not seem as though any time could be
profitably spent in considering the question. It looks, indeed,
as though it would be only another case of arguing about the
politics of the people who live or do not live on the other
side of the Moon.
Yet a close study of the development of life on our Earth
appears to afford considerable indirect and circumstantial
evidence that the course of organic evolution may be very
similar, even where the physical and chemical conditions are
widely different. This similarity is rendered probable by the
fact that organic peculiarities, both internal and external, have
not been developed so much by the inorganic as by the organic
surroundings. The evolution is mainly the result of a struggle
for existence, which must go on wherever there is life. There-
fore if the physical environment be a tolerably permanent one,
favouring the processes of organic chemistry, the resulting life-
forms may be similar, whatever may be the temperature or the
active chemical elements.
On our Earth, Nature has long been unconsciously experi-
menting with innumerable kinds of organic life. Without
either mercy or spite she has pitted one form against the other
Fi<;. 128. Disc OF THE SUN, AUGUST 12, 1903
Showing brilliant calcium flocculi. Middle (H) level. Taken with Hale'a spectroheliograph,
at Yerkes Observatory.
\TBRA;?>
0- r- <E '
UNIVERSITY
or
*J
INHABITED WORLDS 275
under a great variety of local conditions, allowing the fittest to
survive and the rest to perish. The " experiments " have been
ceaselessly carried on for many millions of years, with a super-
abundance of material, and with a physical and chemical
environment that has been almost unchanging.
This being the case, the course of development and final
result may have been inevitable rather than the effects of
chance. Earthly forms of life may be practically duplicated
on a million worlds that were, and are, and are to be.
There is not room in this chapter to go into details on the
question, and it would be out of place in any other part of this
volume. But a few hints may be given as to the way in which
organic life is likely to develop on a world where the condi-
tions prove favourable.
Whatever the temperature and active elements may be, it
seems certain that organic life must be based on the cell or its
equivalent, and that the first cells must originate from and in
non-living compounds of those active elements.
A. The first living forms must be single-celled PROTISTA,
having their home in water or some similar fluid.
The energy necessary to carry on the processes of life must
come from a chemical change similar to the oxidation of tissues.
The wasting tissues must be renewed by the absorption of
soluble inorganic compounds.
Each single-celled organism must go through a life-cycle
ending either in death or in division. This must lead to re-
production by fission, or by some similar process involving a
less expenditure of energy than the original spontaneous
generation. 1
The multiplying individuals must adjust themselves to local
conditions, and thus give rise to varieties, species, etc. When
they have multiplied till food becomes scarce, some will be
compelled to feed on their neighbours. Only those will survive
which can obtain food and protect themselves from being
eaten. The result of this " cannibalism " is a division into
1 And capable of being carried on under less favourable conditions.
276 HOW TO KNOW THE STARRY HEAVENS
plants, which live on soluble inorganic food, and animals,
which live, either directly or indirectly, on the plants.
When single-celled possibilities have all been long and
fully tried, the only possible advance will be found in combina-
tion. Some of the dividing organisms will remain in contact
and partnership, giving rise to many-celled plants and animals.
These compound individuals will by co-operation and division
of labour find greater safety and economy, resulting in a
better living than their simple competing neighbours. They will
therefore get the upper hand, and continue to advance in size
and complexity of organisation.
Nature may be said to have issued two irrevocable decrees
with regard to organic evolution. One of these is that " where
there is no necessity there shall be no development." The
other is that " where there is necessity there shall be either
development or death."
The plants living by the absorption of soluble inorganic
compounds, which are all around them require no special-
sense organs, or apparatus for thinking, moving, eating, digest-
ing, etc., and they do not develop them. But they are usually
compelled to anchor themselves to the sea-bottom where the
surroundings are favourable, to spread themselves out so as to
obtain a large absorbing surface, to protect themselves from
their animal foes, and to modify their methods of growth and
reproduction wherever the local conditions require it.
The animals being compelled to find suitable organic food
or starve will develop means of locomotion and all the
physical and mental peculiarities necessar}^ for obtaining and
utilising the available supply. Like the plants, they will find
it necessary to protect themselves from their animal foes, and
to modify their methods of growth and reproduction wherever
the local conditions require it.
The animals will therefore rise to a higher plane than the
vegetables, and the free-moving and offensive forms will develop
more, in every direction, than the fixed, sluggish, and defensive
forms,
INHABITED WORLDS 277
So far as shape is concerned, there appear to be only two
general organic types possible, either here or in any other
world. These are the radial and the elongated bilateral.
Among the animals, the radial type has given rise, on our
planet, to two branches.
B. One of these is termed the CCELENTERATA. It contains
such forms as the jelly-fishes, sea anemonies, and corals. These
have only one opening to the stomach.
0. The other branch is the ECHINODERMATA. It includes
the crinoids, starfishes, and sea-urchins. They have the stomach
open at both ends.
All the forms in these two branches are either fixed or
sluggish. Other-world forms of this radial type would probably
be the same.
The elongated bilateral type, although very unpromising in
its earlier stages, has much greater possibilities. In fact all
our higher forms of animal life belong to this type.
D. The simplest form is that of a marine worm, which is
little more than a long sack with a hole at each end of it. At
this stage it is naturally a very sluggish animal.
E. When the worm-like animal develops tentacles or arms
around its mouth, it becomes a MOLLUSK, represented on Earth
by the clams, snails, and cuttle-fish. Some of these forms are
rather more active than those already mentioned, but the limit
of advancement is soon reached.
F. When the worm-like form develops a segmented structure,
with a tough skin, and numerous jointed legs arranged along
its two sides, it becomes the more active ARTHROPODA, repre-
sented in our seas by the lobster family and some insects.
Gr. When the same worm-like form retains its simpler
structure but develops an internal skeleton, with a tail and two
pairs of lateral limbs, it becomes a VERTEBRATE fish-like ani-
mal. This is capable of great activity, and appears to be the
highest form of life which can be developed under oceanic
conditions. 1
1 For many millions of years this fish-like vertebrate has made very little
progress with us, in spite of the relative immensity of our oceans and the great
278 HOW TO KNOW THE STARRY HEAVENS
From this it appears probable that on those worlds which
are nearly or entirely covered by water or some similar liquid,
the highest form of life will be a rather stupid fish-like animal
with an internal skeleton, simple organisation, a tail, and two
pairs of lateral fins.
On those planets which have large masses of land rising oat
of the ocean, some forms of life will be gradually crowded out
of the water and modified so that they can live without being
constantly submerged. In the course of time both plants and
animals will spread over the continents and islands, relying on
an occasional rainstorm to keep them from drying up.
On our Earth, only the elongated worm-like type sent repre-
sentatives out of the water to seek a living on the dry land.
Its four branches (D, E, F y and G) now constitute the entire
population of the dry land, as well as all the more active resi-
dents of the ocean. The arthropods and vertebrates have been
the most successful of the dry-land colonists, and have risen,
both physically and mentally, far above their relatives who still
remain below the sea level.
Most of the dry-land ARTHROPODS became parasites of the
land vegetation. 1 As a result of the struggle for existence they
developed into an immense variety of insect-lite. At the same
time they compelled the plants to protect themselves, and so
caused the development of an equally immense variety of
flowering plants. But their complex organisation and parasitic
mode of life limited their size and prevented them from de-
veloping further than the bee and the ant. On other worlds
the same causes would probably result in similar limitations.
It would be a mistake to suppose that the animal with the
most complex organisation is necessarily the highest and most
progressive form of life. The most progressive animal, both
physically and mentally, is likely to be the one which has the
variety of forms which have arisen therein. Its development appears to have
been checked by the limitations of its habitat. Even the land mammals which
have gone back to live in the sea have degenerated, both physically and mentally.
1 Some of them afterward became parasites on other animals.
INHABITED WORLDS 279
very simplest and best arranged machinery that is really
effective in accomplishing the desired ends.
On our world the arthropods, with their many segments and
numerous limbs, were compelled (like the fishes in the sea) to
waste their energies in mere multiplication of non-progressive
species. The fish-like VERTEBRATES, on the other hand, with
their simple, well-arranged, and centralised organisation, and
with the smallest effective number of limbs, made rapid prog-
ress as soon as they had adapted themselves to living on the
dry land. Their gills were replaced by lungs, and their lateral
fins developed into legs, with five toes on each foot. The more
varied conditions to which they were exposed in their new
habitat, combined with the violent struggle for existence which
soon arose, led to great developments in size and strength or in
nimbleness and cunning. Their internal organs became more
effective, and their organs of sense more acute. They developed
into amphibians, reptiles, birds, and mammals. Many of them
became carnivorous, and developed claws and teeth suitable for
their bloodthirsty profession. This led to the survival of those
vegetarian forms which were most successful in defence, con-
cealment, or flight. A great variety of species arose from this
struggle for existence.
Some of the tree-dwelling quadrupeds learned to use their
feet for climbing, and for swinging from tree to tree. When
they were subsequently forced to live on the treeless plains,
they walked upright on their hind legs, and used their front
feet for grasping weapons and tools. Their mental develop-
ment was so much hastened by this new use for their front
feet that they gradually learned to utilise the forces of Nature
in addition to their own strength. They also learned to convey
their thoughts to one another by a constantly increasing variety
of vocal sounds, and mutually to co-operate for the attainment
of any desired end. As they were now able to protect them-
selves from the elements, and from all kinds of difficulties and
dangers, they soon spread from land to land without under-
going any great physical modifications. Their descendants are
280 HOW TO KNOW THE STARRY HEAVENS
now to be found all over the continents and islands of the
Third Planet, and the species is known to science by the name
of Homo sapiens.
Now the innumerable modifications that have, on our Earth,
led from the first protista to the latest man, are entirely the
result of the struggle for existence. This struggle may at the
very first have been entirely physical and chemical. But when
once any particular part of the World became crowded with
living organisms, there arose a much more terrible struggle,
between the different species, and also between the individuals
composing those species. This struggle was one for the neces-
saries of life, such as food, water, air, and light. All kinds
of organic life were blindly and intensely prolific, but the
World was small, and the necessaries of life were strictly
limited in amount. The entire Earth therefore became like
the Black Hole of Calcutta, packed with a struggling mass of
starving and suffocating organisms. For every one that lived
long enough to propagate its species, a -thousand perished in
infancy. Only those that were strong, savage, nimble, cunning,
unscrupulous, or uneatable, could survive and hand down their
peculiarities to their posterity. The surviving forms are there-
fore those which are best fitted to carry on the struggle.
The physical and mental peculiarities which have been most
successful here would probably be most successful in a similar
struggle for existence on any other world. And the course of
organic evolution would therefore be somewhat similar. Hence
we may say, with George Morris :
" There is considerable reason to believe that the beings which
answer to man upon any of the planets of the Universe must at least
approach man somewhat closely in physical configuration. ... It
certainly seems as if a human traveller, if he could make a tour of
the Universe, would find beings whom he could hail as kindred upon
a thousand spheres." *
1 Those who wish to follow up this subject should read an article by Mr.
Morris in the Popular Science Monthly for April, 1904.
INHABITED WORLDS 281
A POET'S DREAM
The astronomer, as such, has nothing to say of the unknown
citizens of these unknown worlds. Accustomed, as he is, to
test his theories by observation, he holds lightly to unprovable
speculations, however probable they may be.
The speculative poet, however, trusts himself in airy flights
that extend far beyond the limits of the known. He not only
wrestles boldly with half-seen facts, but also concerns himself
with invisible probabilities. With an imagination that knows
no fetters except those of natural law, he sees, beyond the
utmost range of telescope and camera, the
" fire of unrecorded stars
That light a heaven not our own."
He beholds, with a certainty that is based on mathematics
and physics
"the hidden gyre
Of bulks that strain in Algol's toils."
He glimpses, with a probability that is born of his earthly
observations, the
" seas that flash on alien eyes
The riven sunlight of Altair."
In many a far-off globe he sees a dawn of life, followed by a
physical and mental evolution which culminates in the develop-
ment of reasoning beings. On many an unknown world he
watches an age of faith slowly change to an age of reason. On
many a sun-kissed planet he hears infantile stories of a one-
world creation give way to more mature discussions of a vast
and abiding Universe. He imagines these unknown phi-
losophers discussing the whence, the where, the what, the
why, and the whither of all things even as some of us do
here.
He sees these lengthy discussions brought to a futile close by
the gathering darkness and cold of everlasting night to be as
282 HOW TO KNOW THE STARRY HEAVENS
fruitlessly brought up, again and again, on other worlds, in
systems yet to come. For the great " Eiddle of the Universe "
can never be fully solved by finite minds. As Olive Schreiner
says of the drama that is being enacted on our own Earth :
" What the name of the play is, no one knows. If there sits a spec-
tator who knows, he sits so high that the players in the gaslight
cannot hear his breathing."
George Sterling, in his immortal " Testimony of the Suns,"
" So dreamt thy sons on worlds destroyed,
Whose dust allures our careless eyes,
As, lit at last on alien skies,
The meteor melts athwart the void.
" So shall thy seed on worlds to be,
At altars built to suns afar,
Crave from the silence of the star
Solution of thy mystery.
" And crave unanswered, till, denied
By cosmic gloom and stellar glare,
The brains are dust that bore the prayer,
And dust the yearning lips that cried."
CHAPTER XXIV
SIZE, IMPORTANCE, SPEED, AND DURATION
SIZE AND IMPORTANCE RELATIVE
" The appearance of things depends altogether on the point of view we oc-
cupy. He who is immersed in the turmoil of a crowded city sees nothing but the
acts of men. . . . But he who ascends to a sufficient elevation . . . discovers that
the importance of individual action is diminishing as the panorama beneath him
is extending. And if he could attain to the truly philosophical, the general point
of view, . . . rising high enough to see the whole world at a glance, his acutest
vision would fail to discover the slightest indication of man, his free will, or his
works. In her resistless onward sweep, in the clock-like precision of her daily
and nightly revolution, in the well-known pictured forms of her continents and
seas, now no longer dark and doubtful, but shedding forth a planetary light, well
might he ask what had become of all the aspirations and anxieties, the pleasure
and agony of life. As the voluntary vanished from his sight, and the irresistible
remained, well might he incline to question . . . whether beneath the vast-
ness, energy, and immutable course of a moving world there lay concealed the
feebleness and imbecility of man. Yet it is none the less true that these contra-
dictory conditions co-exist Free-will and Fate, Uncertainty and. Destiny. It is
only the point of view that has changed, but on that how much has depended."
Dr. J. W. Draper.
THE human family is an ephemeral form of organic life
entirely confined to one insignificant planet in an incon-
spicuous stellar system. And the still more ephemeral individ-
uals composing it are generally cooped up in a small corner of
this little planet. It is therefore very difficult for those who
take an interest in cosmical affairs to get correct and undistorted
ideas as to the relative sizes and importance of the objects com-
posing the Universe. Nor is it easy for them to accept the
teachings of Astronomy with regard to the enormous speed with
which some of these objects move through space, or the im-
mense duration of the heavenly bodies in general. It may not,
284 HOW TO KNOW THE STARRY HEAVENS
therefore, be out of place to conclude our bird's-eye examination
of the Universe with a few words on these subjects.
Man is a very important personage in his own [estimation.
As a general thing he is so wrapped up in the petty details of
his own mundane existence, that he fails to realise his own
insignificance, either in the Universe at large or in the little
World on which he lives and moves and has his being.
Yet a man is only one out of some 1,400,000,000 of similar
beings. And as knowledge and wisdom bring modesty, he who
thinks himself better and more important than his fellows is
generally of very little account. t
The same is true of the entire living race. All the men,
women, and children on Earth are but a handful to those who
have gone before, and will come hereafter in the ages yet to
come. Future generations will look back with pity on our
boasted wisdom and knowledge, even as we do on the wisdom
and knowledge of former times.
The human race, as a whole, believes itself to be the raison
d'etre of the Universe, " the end and aim of all creation."
Yet it is but a thing of yesterday, doomed to perish to-morrow
and be forgotten. For millions of years the Earth spun around
its reeling axis, and circled around its little twinkling star, in
company with a crowd of other planets. It did all this without
the presence of man, and it will continue to circle and spin
when the human family has passed away, like a streak of morn-
ing cloud, into the infinite azure of the past.
Our World is a very mighty world to us. How mighty it
is, only those who have traversed its oceans and continents can
truly realise.
Yet, compared with the rest of the Universe, it is very, very
small.
So small is it that the mind cannot grasp the idea of its
littleness.
SIZE, IMPORTANCE, SPEED, AND DURATION 285
It is as a single leaf, compared with all the leaves of the
forest.
It is as a blade of grass that withereth away, compared with
all the grasses of the World.
It is as a drop of water, compared with all the oceans and
seas.
It is as a grain of sand, compared with a world of similar
grains.
Our Sun is 1,250,000 times as large as our Earth, and con-
tains 330,000 times as much matter.
Though it is more than 90,000,000 miles away, it is bright
enough to make the electric light seem black by contrast.
It is hot enough to turn our entire Earth into fire-mist if it
were dropped into it. It is powerful enough to keep the planet
Neptune in bondage, although thirty times as far from it as
our Earth.
Yet this mighty Sun of ours is only one out of millions of
similar suns. It is only a star among a Universe of stars.
Space is endless limitless bottomless. It has no bounds,
either visible or invisible. It is a sea without surface or
bottom, an ocean without a shore. And our telescopes and
spectroscopes show that, all around us in the depths of this
shoreless ocean, living suns like ours are strewed in hundreds
of millions, while nebulae and dead suns exist beyond all com-
putation.
SPEED IS RELATIVE
When we hear that our World goes around the Sun at the
speed of 18 J miles in a second of time, and that the Solar
System itself is speeding toward the constellation of Lyra at
the rate of 12 1 miles per second, we naturally compare such
motions with the rush of a bullet or cannon-ball. The result
of the comparison is that the statements appear almost unbe-
lievable. But if we change the comparison, and note that the
Earth is seven minutes in moving the length of her own diam-
286 HOW TO KNOW THE STARRY HEAVENS
eter, and that the Sun is 16 hours in doing the same thing, the
celestial velocities seem very moderate. The first comparison
calls to mind the sharp " ping " of an invisible projectile. The
second reminds one of the stately and almost imperceptible
drift of a family of icebergs through the arctic seas.
In this case the figures do not become smaller, but the stand-
point is changed, and that makes a wonderful difference in the
result.
It is true that astronomy shows us instances of extremely
small bodies travelling at even greater speed than the large
ones. But in these cases it will be found that the small bodies
are not moving by any energy of their own, or by any initial
force that soon ceases to act. They are under the continuous
influence of some celestial giant whose power is almost im-
measurably great. The energy exerted is not merely initial
but continuous and cumulative. The push or pull is therefore
unimaginably vast, compared with any force that man can
bring to bear on such an object. This being the case, it is quite
natural and reasonable that the resulting motions should be
almost beyond his comprehension and belief.
DURATION IS RELATIVE
" A generation passeth away,
And a generation cometh,
But the Earth abideth
For ages of ages. Eccles. i, 4 (A. Zazel).
" But yestermorn, O boastful clay,
Thy planet from its parent broke
O, insect of a summer's day,
Thy vaunted glories pass like smoke ! " George N. Lowe.
To some low forms of animal life a day represents an entire
lifetime. In one day an entire generation is born, flourishes,
and dies. 1
1 In some of the single-celled monera the average life of an individual is about
four minutes, so that there are 360 generations in a day of 24 hours. One of our
days is therefore equal to 12,000 years with them.
SIZE, IMPORTANCE, SPEED, AND DURATION 287
Yet, to a man, a day seems a very short period of time
that gets still shorter as he advances in years.
To a youth who is just entering into life, seventy years seem
to make an almost endless stretch of time. There appear to be
hardly any limits to what may be accomplished in threescore-
and-ten long, long years.
But to the old man that life is little more than a dream
of high hopes unfulfilled of noble aspirations that have been
abandoned of great expectations that have come to nought
of tardy realisations that have turned to ashes in the
mouth.
In the lifetime of one individual many events take place
among men, many changes occur in the World on which he
lives.
Yet all the world-wide occurrences during such a lifetime
form but a page of that history which in Egypt and elsewhere
goes back more than 6,000 years.
Six thousand years of human activities almost becloud the
mind. Through the mists of antiquity the early actors loom
vague and vast. To the unenlightened they seem as Gods who
wield the thunderbolt, control the tempest, and forge the chains
of human destiny.
Yet 6,000 years form but a fragment of the history of man
as revealed by the study of his remains. The human family is
very, very ancient. So ancient indeed is it that many people
refuse to accept the evidence they cannot overthrow.
If we assume that 6,000 generations of men have lived on
this Earth and the time cannot have been much less than
that we are utterly bewildered when we endeavour to realise
such an abyss of time.
Yet such an interval is but a watch in the night when we
compare it with the vast geological periods intervening between
the dawn of life on Earth and the days when man first stood
erect on terra firma. It must have taken millions of years to
deposit the Carboniferous rocks alone, and they represent but a
small fragment of geologic time.
288 HOW TO KNOW THE STARRY HEAVENS
Before the dawn of life on this globe there was a period
during which the first gaseous and then molten Earth was but
" a bare lurid ball in the vast wilds of space." During fathom-
less ages it slowly cooled off, till at last the surface became
solid, and the vaporous ocean above was no longer kept off the
blistering surface.
How long that period lasted we are utterly ignorant. For all
we know it may have exceeded geological times as geological
times exceeded the era of man.
Before the Earth was born as a gaseous centre of conden-
sation in a swirling mist, subsequently to shrink into a fiery
globe was a long, long period, during which a vast and shape-
less nebula turned into a flat and symmetrical indrawing spiral.
And before that shapeless nebula was, the Universe is.
As E. A. Proctor says :
" The whole duration of this Earth's existence is but as a single
pulsation in the mighty life of the Univer.se. Nay, the duration of
the Solar System is scarcely more. Countless other such systems
have passed through all their stages, and have died out, untold ages
before the Sun and his family began to be formed out of their mighty
nebula; countless others will come into being after the life has
departed from our system. Nor need we stop at solar systems, since
within the infinite Universe, without beginning and without end, not
suns only, but systems of suns, galaxies of such systems, to higher
and higher orders endlessly, have long since passed through all the
stages of their existence as systems, or have all these stages yet to
pass through."
It appears certain that matter and energy always existed and
always will exist. They were never created and will never be
destroyed. We have reason to believe that through all time
the Universe contains exactly the same number of corpuscles,
the same amount of energy. Suns and worlds come and go,
like bubbles, on the Eiver of Eternity. But the matter of
which they are composed endures for ever and ever. The
energy they contain neither waxes nor wanes. The one and
the other are eternal everlasting imperishable. Science
SIZE, IMPORTANCE, SPEED, AND DURATION 289
teaches us that though the heavens change and the worlds
decay, neither a corpuscle of matter nor an iota of energy will
ever cease to exist.
SUMMARY
We thus see that size, importance, speed, and duration are
all relative terms, denoting attributes that are either great or
small according to the standpoint from which they are viewed.
The object of this work is to enable us to view all subjects
from as many different standpoints as possible, so that we may
not be deceived in the conclusions at which we arrive, about
the Universe in general and our World in particular ; about the
human race as a grand total, and an individual as a minute
fraction of it; about Eternity as a limitless whole, and our
Earth-measured years as microscopic parts thereof.
19
CHAPTER XXY
CONCLUSION
"An undercut astronomer is mad." E. Young.
" Most of the religions of the world are more or less derived from Astronomy
in its astrological childhood. The majority of their deities were once identified
with the sun, moon, planets, or stars. Their temples, vestments, feasts, fasts,
ceremonies, and writings, contain multitudes of celestial fossils which only astrono-
mers can recognise and explain." A. Zazel.
"It is Astronomy which will eventually be the chief educator and emancipator
of the race." Sir Edwin Arnold.
I HAVE now finished an account that is little more than a bare
outline of what Science has to say about the Universe. Is
it not a wonderful story, even when poorly told ? Is it not a
sublime picture, though seen as through a glass, darkly ?
The astronomer of to-day is a cosmopolitan in the widest
sense of the word. He is a citizen of the Great Cosmos a
traveller on the Ocean of Space an explorer of what was but
yesterday an unknown Universe. Though he is physically a
prisoner on Earth, he is mentally free to roam through all the
mansions of the skies. Though he is but one of a multitude
of world-mites, he is the privileged spectator of the greatest of
all the dramas. Though he is but an ephemeron, he can watch
the mystic whirling of the myriad worlds through endless time
and space. In the grandest of all temples he can hear the
sublime " music of the spheres " echoing for ever through
the lofty aisles. From his celestial watch-towers he surveys
the wonders of " the house not made with hands, eternal in the
heavens." He stands before the INFINITE ; he contemplates the
ETERNAL.
The human race owes much more to astronomy and its kindred
sciences than it is aware of. All the production, transportation,
CONCLUSION 291
and distribution of the necessaries of life are regulated by the
clock of the astronomer. Every train that crosses the conti-
nents with speed and safety does it through his observations.
Every ship that crosses the otherwise trackless oceans is guided
to port by his instruments and calculations. His predictions
of astronomical phenomena are published in the "Nautical
Almanac " several years before they occur, so that navigators
may be able to correct the errors of their chronometers in
whatever part of the World they may happen to be.
A single mistake in these predictions may bring death and
disaster in any part of the globe. An improved method of cal-
culation or observation may bring increased speed, certainty,
and safety to the commerce of all the World.
The science of human history is largely indebted to astron-
omy for the correction of its dates. .For some of the eclipses,
comets, etc., which are mentioned in ancient documents and
traditions, have been identified by calculating back, and the
exact dates have been ascertained. When these have once
been fixed, all the neighbouring dates can be adjusted to those
which have been ascertained astronomically.
Some departments of science appear, at first sight, to be
practically useless, because they have, or appear to have, no
direct bearing on the welfare of the race. Yet even these bring
indirect benefits which are too vast to be easily realised. Pure
science can be cultivated only for itself, but it forms the foun-
dation on which all practical science is based. Then the les-
sons that science teaches, on the art of getting at the truth, are
as valuable as its most practical discoveries and practicable
inventions. This is especially the case with astronomy. Even
the necessary ills of life are lessened by a knowledge of the
heavens, for in the presence of the illimitable and eternal Uni-
verse it seems absurd to worry about the little earthly troubles
that we cannot remedy. We learn to accept the inevitable and
make the best of it.
It may indeed be truthfully said that a fair knowledge of
astronomy and geology will double the pleasures of life and
292 HOW TO KNOW THE STARRY HEAVENS
halve its troubles. At the same time it will entirely remove
the creed-made terrors of death.
There are not many of us who can do much toward gaining
fresh knowledge of the secrets of Nature. But there is no
reason why we should not enlighten, broaden, and refresh our-
selves by taking an interest in the scientific discoveries which
are revolutionising the world and revealing the Universe to
man.
The study of the Universe will not only make us enlightened
citizens of the Great Cosmos, but will also make us better citi-
zens of our own World. It will do this by teaching us to observe
correctly the surrounding social and economic phenomena,
instead of blindly trusting to the assertions of prejudiced and
perhaps interested persons. It will also train us to reason cor-
rectly and impartially as to the causes and effects of the
observed phenomena. We find ourselves, at the commence-
ment of the twentieth century, confronted by serious industrial,
economic, and social problems which demand solution at our
hands. These problems are largely the result of scientific
instruments of production and distribution, invented and
developed during the last two centuries. We cannot solve
these problems satisfactorily and equitably till we recognise
the fact that human progress is subject to evolution that it
is in fact ruled by natural laws just as inexorable as those
which govern suns and worlds. It is therefore necessary for
us to ascertain what these laws are, and then to solve our in-
dustrial and social problems in accordance with them. When
this is done, our wonderful advance in the arts and sciences
will be paralleled by as rapid an advance toward universal
prosperity and happiness. But not before.
NOTE. Those who wish to continue the study of the starry heavens will do
well to get the popular works of Airy, Ball, and Serviss; also Comstock's
" Text-book of Astronomy," which, at its close, gives a list of some of the best
works on astronomy, both general and special.
CONCLUSION 293
ASTRONOMY
BY GEORGE N. LOWE
(By permission')
Great Antidote for ignorance and fears,
We look to thee to lead us to the day.
Before thy light the darkness melts away
Thy ceaseless labour Life's great pathway clears.
The shackles fall as pass the stately years,
Thy gaze uplifts, lo ! Yega's distant day
Comes, captive, where thy mystic colours play
The sombre gloom of ages disappears.
What though the thrones of false gods shake and fall,
Though useless, hoary, man-made creeds may fade ?
Calm Reason knows no sorrow, reck, or ruth.
Thy touch, Boon Science, liberates the thrall ;
Thy broadening beam illumes the unknown shade ;
Patient, thy finger pointeth to the Truth.
APPENDIX A
FACTS AND FANCIES CONCERNING MATTER
" What is Matter ? Never mind.
What is Mind ? No matter." Old Queries.
" What is Matter ? Only a cloud of Corpuscles.
What are Corpuscles ? Only Electricity.
What is Electricity ? Only Matter.
What are they all ? No matter. Never mind ! " New Queries.
ONLY A ROCK
TAKE up a small rock in your hand and examine it care-
fully with the naked eye.
It appears to consist of a number of irregular granules, dif-
fering in size and shape, but alike in colour and texture. It is
only a piece of rock, rough, heavy, more or less hard and com-
pact, and altogether insignificant.
Such a rock might serve a teamster very well to throw at
his off leader, or a small boy might use it as a nucleus for a
vicious snow-ball, but otherwise it is of no value to man or
beast.
TWO STANDPOINTS
Yet these ideas concerning its insignificance are all owing
to the fact that we view it from a human standpoint, without
even the aid of science.
If we could examine it from the standpoint of one who
possessed the all-seeing eye popularly attributed to some of the
Gods, we should perhaps come to very different conclusions
concerning its size, condition, and importance.
296 HOW TO KNOW THE STARRY HEAVENS
In order to do this, we shall have to increase our powers of
vision and analysis by resorting to the microscope and other
scientific instruments.
A MAGNIFIED ROCK
On applying a powerful magnifying-glass to the rock, we
find that it no longer appears small and insignificant. In fact
it is now so large that we can examine only a small part of it
at once.
Its granulated surface has swelled into rugged rock-masses
divided by narrow gulches and clefts. The surface of these
masses of rock has the same granulated appearance that the
whole rock had to the naked eye.
We will now select the smallest visible speck, and examine
it with the microscope. The result is that the speck, which
was almost invisible with the single magnifying-glass, is now
a huge mass of rocky hills separated by gloomy gorges.
On closely observing the rocks which compose these hills, we
see that the whole mass is honeycombed with crevices which
were invisible before. Each mighty rock is seen to be com-
posed of small granules loosely connected together.
A WORLD IN ITSELF
By vastly increasing the power of our microscope the hills
become mountain-chains whose lofty peaks extend away into
the remote distance. The stone which could be held in the
hand has become a world in itself, shutting out the firmament
from view.
Again and again we select the smallest visible granule, and
subject it to examination with higher magnifying power.
Each time we do so the almost invisible particle selected swells
into an enormous mass that fills the field of view. Each suc-
cessive particle is seen to consist of hills and gorges of more
or less solid rock, composed of scarcely visible granules. But
the substance of these granules is still the same as that com-
posing the whole rock.
FACTS AND FANCIES CONCERNING MATTER 297
The magnifying powers of the most powerful microscope in
existence are at last exhausted. We have to continue our
examination by means of the spectroscope and other instru-
ments, and view the results of our investigations with the eye
of the imagination.
Confining ourselves to the smallest sub-granule revealed by
the most powerful microscope, we see it gradually unfold itself
as the magnifying power of the imagination is applied to it.
When it becomes too large for minute examination, we select
an almost invisible particle of it, and watch it grow till it fills
the entire field of view. Again and again we do the same
thing, each successive particle getting too large for inspection
as it swells under the scrutiny of the scientific imagination.
As this process goes on, we notice a progressive change, not
in the substance, but in the structure of what we are examining.
It slowly loses its original solid appearance and becomes a
dense nebulous haze.
MOLECULES
This haze gradually opens out, and finally resolves itself into
a universe of small separate bodies which are commonly known
as molecules. These appear to float in empty space without
touching one another.
ATOMS
As the magnifying power of our imagination goes on increas-
ing, each molecule is seen to be a group of shining atoms,
clinging together in " radical " bunches, yet avoiding actual
contact. These atoms are altogether different in appearance
and properties from the molecules which they compose. They
may be sorted out into several different species, the individual
atoms of each kind being all absolutely alike, but different in
size, weight, and other particulars from those of the other
species.
CAPTIVE CORPUSCLES
The question now arises, What are these different kinds of
atoms which constitute the molecules of which our rock is
298 HOW TO KNOW THE STARRY HEAVENS
built up ? Are they single and indivisible, independent and
unrelated, or are they, too, composed of still smaller particles?
In order to decide this question we pick out a single atom in
one of the molecules and confine our attention to it exclusively.
At the same time we once more increase the separating power
of the imagination.
The atom now loses its indivisible character and is seen to
consist of a star-cluster of minute corpuscles. These appear to
have a regular orbital motion, at planetary distances, around
their centre of gravity. They are kept together, and yet
separate, by a combination of forces which is not yet under-
stood.
These sub-elementary corpuscles are all identical in form,
weight, and attributes. The only suspicion of difference is that
they act as though one half of them were positively, and the
other half negatively, electrified. They seem to cling together
in pairs and form alternate layers around the centre of the
cluster, the layers being far apart and sparsely occupied.
We now leave the atom we have just resolved into corpuscles,
and devote our attention to the other species of atoms which
build up the molecules of matter. They are all resolvable into
star-clusters of corpuscles which are exactly the same as those
which composed the atom first examined. The only difference
appears to be in the number and arrangement of the corpuscles
which compose the different kinds of atoms. The smallest
known atoms contain about a thousand corpuscles.
The outside layer of corpuscles in an atom appears to be
always composed of negatively electrified corpuscles, some of
which have the power of flitting from one atom to another,
and of flying off into space as free and independent corpuscles.
FREE CORPUSCLES
Besides the corpuscles which go to build up the various
atoms, there is an immense multitude of negatively electrified
corpuscles which exist in a free state. The atoms of matter
FACTS AND FANCIES CONCERNING MATTER 299
move through this " dust-cloud " of free corpuscles as readily as
a sieve moves through water without displacing it. The other-
wise unoccupied space between the atoms of matter is filled to
saturation with these free negative particles, which carry the
vibrations of ponderable matter from one atom to another.
They form the luminiferous ether which fills all space.
ULTIMATE PARTICLES
We now seem to have at last reached a stage where all
matter is identical in substance, form, weight, appearance, and
properties. The ultimate particles of which matter is composed
appear to be revealed to the eyes of the imagination. But we
are still entirely in the dark as to the nature of these ultimate
and identical particles, and the reason why they group them-
selves as they do, to build up the atoms and molecules of
ponderable matter. We are now face to face with the unsolved
Riddle of the Universe. We are dealing with the mysterious
astronomy of the atoms. We have found the simple bricks out
of which the elaborate structures of the Universe are built, but
cannot tell whence, nor why, nor what they are. Even the
imagination has at last reached the limit of its power, and we
are hopelessly lost in trying to solve the great Problem of
Substance.
A TINY UNIVERSE
Now, for all we know to the contrary, the nebulous cloud of
matter we have been examining may be a Universe like ours.
Its molecules may be aggregations of atomic star-clusters like
those revealed by the telescope. Its electrical corpuscles may
be suns like ours, sending forth their radiant energy to invisible
worlds, some of which may be inhabited by unreasoning
creatures like man.
If such should be the case (and it would not be very easy to
disprove it), then an inhabitant of one of these invisible worlds
probably thinks that his Earth is the only one in existence ;
300 HOW TO KNOW THE STARRY HEAVENS
that he is the one for whom all things were created ; that his
eternal well-being is the chief concern of the Creator ; and that
his moment of life is a big part of Eternity.
So much for the rock we have been studying. Let us now
throw it away and turn our attention to some of the more
pressing problems of lunar politics.
WHO KNOWS?
Yet before doing so I would like to ask, How do you know
that our mighty Universe is not a similar pebble on the shore
of some gigantic world ? It may seem to some that absurdity
could go no further than this suggestion. Yet it is a surmise
logically based on the generally accepted infra-atomic " star-
clusters" of our foremost scientists. As such I cheerfully
submit it to them for their prayerful consideration. If their
corpuscular theory of atoms is true and I should be the last
to deny it then this celestial application of it may be true
also. Or it may not. ^ Quien sale ?
THE GREEK ALPHABET 301
APPENDIX B
THE GREEK ALPHABET
THE study of the Star Charts requires a knowledge of
the Greek alphabet. It is therefore printed here for
reference, with the name and sound of each letter.
GREEK
A a
B j3
r y
A d
E s or e
Z f
H r)
e #or 6
1 i
K K
A X
M 11
N v
*
O o
n TT
p P
2 a- or $
T T
Y v
*
X
NAME
ENGLISH
Alpha
Beta
a
b
Gamma
Delta
g
d
Epsilon
Zeta
u
z
Eta
e
Theta
th
Iota
i
Kappa
Lambda
k
1
Mu
m
Nu
n
Xi
X
Omicron
6
Pi
Rho
P
r
Sigma
Tau
s
t
Upsilon
Phi
Chi
u
ph
ch
Psi
Omega
ps
o
302 HOW TO KNOW THE STARRY HEAVENS
APPENDIX C
THE LUNAR CRATERS
EXPLANATION OF THE FIRST FOUR TABLES
THE number before the name of a crater indicates its place on
the charts.
The craters which have no number before them are lettered on
the charts.
Small odd numbers (1 to 81) indicate craters on the north half of
the western chart.
Large odd numbers (83 to 169) indicate craters on the south half
of the 'western chart.
Small even numbers (2 to 68) indicate craters on the north half of
the eastern chart.
Large even numbers (70 to 176) indicate craters on the south half
of the eastern chart.
The names in italics indicate craters near the centre of the lunar
disc.
The names in roman type indicate craters near the circumference
of the lunar disc.
Small numbers in parentheses, ( ), denote the diameter of the
crater in miles.
Large numbers in brackets, [ ], denote the extreme height of the
rampart (in feet) above the floor of the crater.
TABLE I
CRATERS ON THE NORTHWEST QUARTER OF THE MOON
[See Chart F]
1 Barrow (40)
3 Strabo
5 Aristoteles (60), [11,000]
7 Endymion (80)
9 Atlas (55), [11,000]
11 Hercules (46), [11,000]
13 Berg
15 Eudoxus (40)
THE LUNAR CRATERS
303
17 Messala
19 Cassini (36), [4,000]
21 Gauss (110)
23 Berzelius
25 Thesetetus
27 Gemiims
29 Aristillus (34), [11,000]
Posidonius (60), [6,000]
31 Autolycus (23), [4,000]
33 Linne
35 Burckhardt
37 Tralles
39 Cleomenes (80), [10,000]
41 Roemer
43 Macrobius (40), [13,000]
45 Bessel
47 Maraldi
49 Sulpicius Gallus
51 Peirce
53 Vitruvius
Proclus
55 Alhazen
57 Dawes
Menelaus (20)
59 Hansen
61 Picard
Plinius (30), [6,000]
Manilius (25)
63 Condorcet
65 Julius Ccesar
67 Firmicus
69 Taruntius
71 Silberschlag
73 Hyginus
75 Ariadceus
77 Agrippa (30)
79 Triesnecker (20)
81 Godin (22)
TABLE II
CRATERS ON THE SOUTHWEST QUARTER OF THE MOON
[See Chart F]
83 Webb
85 Messier
87 Delambre
89 Hipparchus (100)
91 Hypatia
93 Langrenus (90), [10,000]
95 Torricelli
97 Taylor
99 Isadorus
101 Guttemberg (45)
103 Goclenius (28)
Theophilus (64), [18,000]
105 Cyrillus (60)
107 Albategnius (65), [15,000]
109 Abulfeda
111 Vendelinus
113 Catharina (65)
115 Almamon
117 Sacrobosco
119 Santbeck
121 Fracastorius
123 Apianus
125 Humboldt [16,000]
Petavius (78)
127 Pontanus
129 Werner (45)
131 Aliacensis [16,000]
133 Piccolomini [15,000]
135 Zagut
137 Reichenbach
139 Walter (100)
141 Lindenau
143 Gemma
145 Frisius
147 Neander
149 Rabbi Levi
304 HOW TO KNOW THE STARRY HEAVENS
151 Stiborius
153 Furnerius
155 Rheita
157 Maurolycus (150), [14,000]
159 Stofler (110)
161 Fabricius
163 Clairaut
165 Pitiscus
167 Bacon
169 Curtius
TABLE III
CRATERS ON THE NORTHEAST QUARTER OF THE MOON
[See Chart E]
2 Philolaus
4 Pythagoras
6 Fontanelle
8 Condamine
Plato (60), [7,000]
10 Harpalus
12 Bianchini
14 Sharp
16 Leverrier
18 Helicon
20 Mairan
22 Herschel(17)
24 Gruithuisen
26 Lichtenberg
Archimedes (52), [4,000]
28 Delisle
30 Beer
32 Timocharis (23), [7,000]
34 Diophantus
36 Lambert (17)
38 Euler (19)
Aristarchus (28)
40 Herodotus
42 Pytheas
44 Tobias Mayer
46 Eratosthenes (37), [16,000]
48 Bessarion
50 Marius
52 Stadius
Copernicus (56), [12,000]
54 Galileo
Kepler (22)
56 Reiner
58 Schroeter
60 Reinhold
62 Kunowsky
64 Encke
66 Hevel
68 Gambert
TABLE IV
CRATERS ON THE SOUTHEAST QUARTER OF THE MOON
[See Chart E]
70 Landsberg
72 Mosting
74 Lalande
76
78
80
Fra Mauro
Parry
Bonpland
_< 'Saiy o/ Ctt*apk< e 'Pit A
Rai * *
CHART E. EASTERN HALF OF MOON
C=>c-_ C^> <->
g? -J
^ tA or i" ^^%^,
touViiL^K_\^^
a ^.-V;P!S-.- .^i-
^e-<ri
D> P P *
r> '/ g "?
ro p^
<=4 W-* ,O ^
". -J13 '' n*, L * V 1
CHART F. WESTERN HALF OK MOON
THE LUNAR CRATERS
305
82 Flamsteed
84 Damoiseau
Grimaldi (150)
86 Euclides
Ptolemy (115)
88 Guerike
90 Letronne
92 Hansteen
Alphons (83)
94 A Ipetragius
96 Lassell
98 Billy
Arzachel (65)
100 Gassendi (54)
102 Fontana
104 Thebit (30)
106 Birt
108 Nicollet
110 Bullialdus (38),
112 Agath archides
114 Mersenius (40)
116 Eichstadt
118 Purbach (60)
120 Regiomontanus
122 Pilatus
124 Mercator
126 Vitello (24)
128 Vieta
[8,000]
130 Hell
132 Cichus
134 Lexell
136 Ball
138 Capuanus
140 Lagrange
142 Lacroix
144 Piazzi
146 Bouvard
148 Heinsius
150 Saussure
Tycho (54), [17,000]
152 Hainzel
Schickard (134), [9,000]
154 Wilhelml.
156 Inghirami
158 Maginus (100)
Wargentin (53)
160 Longimontanus
162 Schiller
Clavius (140), [17,000]
164 Scheiner
166 Bettinus
168 Bailly
170 Kircher
172 Moretus
174 Casatus
176 Newton [24,000]
TABLE V
ALPHABETICAL LIST OF CRATERS
Abulfeda, 109
Agatharchides, 112
Agrippa, 77
Albategnius, 107
Alhazen, 55
Aliacensis, 131
Almamon, 115
Alpetragius, 94
Alphons
Apianus, 123
Archimedes
Ariadceus, 75
Aristarchus
Aristillus, 29
Aristoteles, 5
Arzachel
Atlas, 9
Autolycus, 31
Bacon, 167
Bailly, 168
Ball, 136
Barrow, 1
Beer, 30
20
Berzelius, 23
Bessarion, 48
Bessel, 45
Bettinus, 166
Bianchini, 12
Billy, 98
Birt, 106
Bonpland, 80
Bouvard, 146
Bullialdus, 110
Burckhardt, 35
Burg, 13
306 HOW TO KNOW THE STARRY HEAVENS
Capuanus, 138
Hainzel, 152
Messala, 17
Casatus, 174
Hansen, 59
Messier, 85
Cassini, 19
Hansteen, 92
Moretus, 172
Catharina, 113
Harpalus, 10
Hosting, 72
Cichus, 132
Heinsius, 148
Clairaut, 163
Helicon, 18
Neander, 147
Clavius
Hell, 130
Newton, 176
Cleomenes, 39
Hercules, 11
Nicollet, 108
Condamini, 8
Herodotus, 40
Condorcet, 63
Herschel, 22
Parry, 78
Copernicus
Hevel, 66
Peirce, 51
Cur-tins, 169
Hipparchus, 89
Petavius
Cyrillus, 105
Humboldt, 125
Philolaus, 2
Hyginus, 73
Piazzi, 144
Damoiseau, 84
Hypatia, 91
Picard, 61
Dawes, 57
Piccolomini, 133
Delambre, 87
Inghirami, 156
Pilatus, 122
Delisle, 28
Isadorus, 99
Pitiscus, 165
Diophantus, 34
Plato
Julius Ccesar, 65
Plinius
Eichstadt, 116
Pontanus, 127
Encke, 64
Kepler
Posidonius
Endymion, 7
Kircher, 170
Proclus
Eratosthenes, 46
Kunowsky, 62
Ptolemy
Euclides, 86
Purbach, 118
Eudoxus, 15
Lacroix, 142
Pythagoras, 4
Euler, 38
Lagrange, 140
Pytheas, 42
Lalande, 74
Fabricius, 161
Lambert, 36
Rabbi Levi, 149
Firmicus, 67
Landsberg, 70
Regiomontanus, 120
Flamsteed, 82
Langrenus, 93
Reichenbach, 137
Fontana, 102
Lassell, 96
Reiner, 56
Fontanelle, 6
Letronne, 90
Reinhold, 60
Fracastorius, 121
Leverrier, 16
Rheita, 155
Fra Mauro, 76
Lexell, 134
Roemer, 41.
Frisius, 145
Lichtenberg, 26
Furnerius, 153
Lindenau, 141
Sacrobosco, 117
Linne, 33
Santbeck, 119
Galileo, 54
Longimontanus, 160
Saussure, 150
Gambert, 68
Scheiner, 164
Gassendi, 100
Macrobius, 43
Schickard
Gauss, 21
Maginus, 158
Schiller, 162
Geminus, 27
Mairan, 20
Schroeter, 58
Gemma, 143
Manilius
Sharp, 14
Goclenius, 103
Maraldi, 47
Silberschlag, 71
Godin, 81
Marius, 50
Stadius, 52
Grimaldi
Maurolycus, 157
Stiborius, 151
Gruithuisen, 24
Menelaus
Stofler, 159
Guerike, 88
Mercator, 124
Strabo, 3
Guttemberg, 101
Mersenius, 114
Sulpicius Gallus, 49
THE LUNAR CRATERS
307
Taruntius, 69
Taylor, 97
Thesetetus, 25
Thebit, 104
Theophilus
Timocharis, 32
Tobias Mayer, 44
Torricelli, 95
Tralles, 37
Triesnecker, 79
Tycho
Vendelinus, 111
Vieta, 128
Vitello, 126
Vitruvius, 53
Walter, 139
Wargentiu
Webb, 83
Werner, 129
Wilhelm I, 154
Zagut, 135
CHART G. THE C
Astrological He
to explain t
PERSIAN, JEW
RE
P&le Nord - -
North Pole.
Voye Lacte
Milky Way.
Hydre - -
Hydra.
Taureau
Taurus; Bull.
Orion ; Nemrod -
Orion ; Nimrod.
Gemeaus
Gemini.
Crab ou Cancer
Crab or Cancer
Bellier; Agneau de
Ram ; Lamb of God ;
Dieu
Aries.
Pers^e; Cherubin -
Perseus ; Cherubim.
Etable d'louseph
Joseph's Stable ; Auriga.
Lion -
Lion; Leo.
Nortnern Hemisphere.
Translation.
Ours ; Sanglier ; Ane ;
Typhon -
Poissons -
Andromede
Dragon des Hesperides
Vierge; Eve; Sybille;
Isis, &c.
Bootes; Adam; Osiris;
Couronne
Hercule
Serpent d'Eve ; Ahri-
man ; Satan
Bear ; Boar ; Ass ;
Typhon.
Pisces the Fishes.
Andromeda.
Dragon of the Hesperides
Virgin ; Eve ; Sybil ;
Isis, &c.
Bootes ; Adam ; Osiris.
Corona Borealis.
Hercules.
Eve's Serpent ; Ahri-
manes; Serpentinus.
STELLATION FIGURES.
of the
of the Ancients
r yslertes of the
AND CHRISTIAN
ONS.
Southern Hemisphere.
Translation,
hien ; Sirius
Dog; Sirius.
Corbeau de No
Noah's Raven ; Corvus
ridan ...
Eridanus.
Verseau ...
Aquarius, the Water-
aleine ...
Whale ; Cetus.
bearer.
il - - -
Nile.
Capricorne
Capricornus.
oupe ...
Crab; Cup.
Sagittaire
Sagittarius, the Archer
aisseau ; Argo ; Arche
Vessel ; Argo ; Navis ;
Voye Lact6e
Milky Way.
Ark.
Scorpion -
Scorpio.
uiopus -
Canopus.
Balance
Scales; Libra.
.le Sud - -
South Pole.
INDEX
ABSORPTION or STARLIGHT, 84
Absorption spectra, 92
Airy, Sir George, 26, 39
Aldebaran, 103
Algol, 108
Allen, Dr. F. J., 273
Alpha Centauri, 53, 78
Alpha Draconis, 147
Alphonso, King, 20
Alt-azimuth telescope, 153
Andromeda, nebula in, 122
Angles, measurement of, 31, 39
Angular diameter, 41
Aphelion, 160
Apocalypse, 17, 26, 239
Apparent motions, 4
Appearances, superficial, 1
Aratus, 118
Arc, chord of, 41 ; of circle, 40
Arc problems, 47
Aries, First Point of, 10, 148
Aristarchus, lunar crater, 264
Aristotle, 163
Ascension, right, 149
Asteroids, 29, 61, 64
Astronomy, Egyptian, 16; Greek, 16,
42 ; Hindu, 23, 43
Atomic theory, 192
Autumnal equinox, 7, 139
BALANCE, TORSION, 38
Base line, 31, 32, 34
Becquerel rays, 197
Bede, Venerable, 17
Beta Lyrae, 108
Bifrost, Bridge of, 87
Binaries, 108, 110
Blood discs, stack of, 73
Brahe, Tycho, 19
Bridge of Bifrost, 87
Byron, Lord, 188
CALCIUM FLOCCOLI, 130
" Canals " of Mars, 226
Cannon-ball, speed of, 71
Canopus, 104
Canopy theory, 16
Celestial distances, measurement of,
32
Celestial equator, 7, 119
Celestial latitude and longitude, 150
Chariot of imagination, 53, 136, 220
Chord of arc, 41
Chromosphere, or sierra, 60, 129
Circle, arc of, 40; meridian, 152
Clavius, lunar crater, 253
Clouds, Magellanic, 122
Clusters of stars, 1 1 1
Colliding stars, 110, 206, 237
Colours of stars, 98,111
Comets, 221
Comparisons, planetary, 69, 77
Constellations, 115, 137
Copernican system, 24 .
Copernicus, lunar crater, 263
Corona, 60, 131, 176
Corpuscles, or negative particles, 89, 199
Craters, lunar, 245, 253, 254, 264
Creation, 18
Creationism, 180
Crookes, Sir William, 179, 196
Crystal spheres, 18
DARK STARS, 107, 135
Darwin, Charles, 201
Darwin, George, 204, 213
Declination, north and south, 149
DeQuincey, Thomas, 77
310
INDEX
Dipper, the, 14
Distances, estimating, 30 ; measurement
of celestial, 32 ; measurement of in-
accessible, 31, 43 ; of stars, 123
Distribution of stars and nebulae, 114,
121
Diurnal motion, 4
Double stars, 108, 110; spectroscopic,
108
Draco, 117
Draper, Dr. John W., 22, 156, 178, 265,
283
Drift, solar, 111 ; stellar, 113, 147
Duffield, Prof., 174
EARTH, 62, 69, 139 ; centre of system,
15 ; measuring the, 31 ; revolution of,
23, 138; rotation of, 23, 138; shape
of, 3 ; weight of, 38
" Ecclesiastes," 286
Eclipses, 11, 146
Ecliptic, 8, 9, 119, 138
Egyptian astronomy, 16
Electro-magnetic theory, Maxwell's,
195
Electronic theory, 200
Elements, in sun, 1 29 ; periodic system
of, 192
Ellipse, 158
Equator, celestial, 7, 119
Equatorial telescope, 12, 150
Equinoxes, 7, 139; precession of, 141,
174
Eros, 33
Estimating distances, 30
Ether, 89, 171, 191, 195
Evolution of organic life, 201, 274
Evolution of solar system, 208
Evolution, tidal, 202, 213
FACUL,E AND FLOCCULI, 127, 130
" Faust," Goethe's, 63
"Faustus," Marlowe's, 21, 136
Fibre, quartz, 75
Firmament, massive, 15, 16
Flames, solar, 59, 130, 176
Flat-world ideas, 15
Fleming, Prof. J. A., 190
Flocculi and facute, 127, 130
Fraunhofer, Joseph von, 194
GALAXY, the, 56, 120
Galileo, 169, 258; his laws of motion, 164
" Genesis," 15, 82, 87
George, Henry, 155, 163
Goethe's " Faust," 63
Gravitation, law of, 167
Great Bear, 14, 120
Great Pyramid, 147
Greek astronomy, 16, 42
HAECKEL, ERNST, 174, 207, 217
Helium, 197
Hercules, cluster in, 111
Herschel, Sir William, 185
Hindu astronomy, 23, 43
Holden, Dr. Edward S., 22
Human laws, 156
INERTIA, 164
"Jos," 17
Jupiter, 27, 64, 69, 233
KANT, IMMANUEL, 184
Kathode rays, 196
Keeler, Prof. James E., 122
Kepler, Johann, 258; Laws of, 157
Kinetic theory of substance, 194
Kirchhoff, Gustav R., 194
Koran, the, 17
LAND-SURVEYING, 31
Laplace, Pierre, 184
Latitude, celestial, 150
Lavoisier, Antoine L., 193
Law of gravitation, 167
Law of substance, 192
Laws, human, 156; of motion, 164; of
nature, 155
Life, evolution of organic, 201, 274
Light, refraction of, 89 ; speed of, 54,
72
Light waves, lengthening of, 84 ; violet,
73, 91
Light years, 68
INDEX
311
Line of sight, motion in, 100
Locomotive, speed of, 84
Lodge, Sir Oliver, 200
Longitude, celestial, 150
Lowe, Geo. N., 85, 156, 286, 293
Lunar craters, 245, 253, 263, 264
Lunar mountains, 260
Lunar plains, 245
Luther, Martin, 23
Lyre, constellation of, 112
MAGELLANIC CLOUDS, 122
Magnitude, stellar, 102, 103
Marlowe's "Faustus," 21, 136
Mars, 27, 63, 69 ; " canals " of, 226
Mass and weight, 36
Massive firmament, 15, 16
Matter, 89, 191, 295; pyknotic theory
of, 195
Maunder, E. W., 118, 120
Maxwell's electro-magnetic theory,
195
Mayer, Robert, 193
Measurement, of angles, 31,39 ; of celes-
tial distances, 32 ; of inaccessible dis-
tances, 31, 43 ; of the earth, 31
Mercury, 27, 69
Meridian circle, 152
Meteorites, 220, 230
Meteors, 230
Midsummer solstice, 8
Milky Way, 56, 120
Millikan, R. A., 198
Milton, John, 53, 120, 223, 224, 243,
271
Mira Ceti, 108
Moon, the, 244; birth, 257; distance,
45; motions, 11, 23; size and mass,
35
Morris, George, 280
Motion, diurnal, 4 ; in line of sight,
100; laws of, 164; of sun, 6, 7
Motions, apparent, 4
Mural circle, 1 53
NADIR, 5
Nasmyth, James, 257
Nature, laws of, 155
Nebulae, 12 J -123; classes of, 97; dis-
tribution of stars and, 114, 121;
planetary, 97
Nebular hypothesis, 184, 207
Negative particles, 89, 199
Neptune, 66, 69
New stars, 109
Newcomb, Prof. Simon, 68, 77, 84, 114
Newton, Sir Isaac, 124, 162; his law of
gravitation, 167
North and south declination, 149
Nutation, 175
OBLIQUITY OF -ECLIPTIC, 8, 138
Organic life, evolution of, 201, 274
Orientation of pyramid, 147
Orion nebula, 123
PAPER, pile of, 72 ; roll of, 77
Parallax, 44
Particles, negative, 89, 199
Pascal, Blaise, 84
Passover, spring, 7, 139
Perihelion, 140, 160
Periodic system of elements, 192
Perturbations of planets, 171
Photographing stars, 83
Photosphere of sun, 59, 126
Planetary comparisons, 69, 77
Planetary nebulae, 97
Planets, 3, 61, 211; comparative dis-
tances, 27, 33, 77 ; density, mass, and
size, 35, 36 ; inferior and superior,
27, 28, 61 ; motions of, 11, 138; move
in ellipses, 29, 157 ; order of, 26 ;
perturbations of, 171; real distances
of, 29, 33, 68
Plato, lunar crater, 263
Pleiades, the, 103, 120
Pointers, the, 14
Polaris, 14, 103, 111
Pole-stars, different, 141, 147
Poles of rotation, 140
Precession of equinoxes, 141, 174
Prisms, 87
Proctor, Richard A., 85, 118, 124, 125,
288
Prominences, solar, 59, 130, 176
312
INDEX
" Psalms," the, 57
Ptolemaic system, 1 8
Ptolemy, 42, 118
Pyknotic theory of matter, 195
Pyramid, the Great, 147
Pythagoras, 23
QUARTZ FIBRE, 75
RADIAL MOTIONS, 100
Radian, 40
Radiant energy of sun, 133
Radiation, spectrum, 92
Radium, 198
Radius vector, 160
Railroad to Neptune, 71 ; to nearest
star, 75
Rainbow, 87
Rays, Becquerel, 197 ; kathode, 196
Red light-waves, 91
Refraction of light, 89
Repulsion, 176
Reversing layer of sun, 129
Revolution of the earth, 23, 138
Revolving wheel, 75
Right Ascension, 149
Ring nebula in Lyra, 122
Rontgen rays, 196
Rotation, of the earth, 23, 138 ; of
planets, 138, 209; of sun, 129; poles
of, 140
SATELLITES, or Moons, 61, 62, 65
Saturn, 27, 64, 69
Schaeberli, Prof., 122
Schiaparelli, 266
" Seasons, The," 229
Seasons on the earth, 139
See, Dr. J. J., 84, 101
Serviss, Garrett P., 120
Shakespeare, 140
Shelley, Percy B., 57, 205
Shooting stars, 230
Sierra, or chromosphere, 60, 129
Sight, motion in line of, 100
Signs of zodiac, 10, 137
Sine of angle, 43
Sine problems, 49
Sirius, 68, 78, 103
Solar flames or prominences, 59, 130,
176
Solar system, drift of, 111 ; evolution
of, 208
Solstice, midsummer, 8; winter, 140
Spectroscope, 88, 194
Spectroscopic binaries, 108
Spectrum, 88 ; continuous, 92 ; of nebu-
lae, 96; stellar, 95; of star-clusters,
96
Spectrum, absorption, 92
Spectrum analysis, 93
Spectrum, emission, or radiation, 92
Spectrum, flash, of sun, 129
Spencer, Herbert, 201
Spheres, crystal, 18; umbrella, 4
Spider's thread, 74
Spiral nebulas, 98, 122
Spots in the sun, 127
Spring passover, 7, 139
Starlight, absorption of, 84
Stars, 3 ; beyond planets, 26 ; classes
of, 98; clusters of, 111; colliding,
110, 206, 237; colours of, 98, 111;
dark, 107, 135; distances of, 23; dis-
tribution of, 114, 121; double, 108,
110; drift of, 113, 147; magnitudes,
102, 103 ; nearest, 34, 68 ; new, 109 ;
number of, 82 ; photographing, 83 ;
telescopic, 83 ; trails, 13; variable,
107 ; visible, 55, 82
Steele, J. D., 167
Stellar drift, 113, 147
Sterling, George, 53, 84, 102, 109, 126,
205, 281, 282
Substance, law of, 192; theories of,
194, 195
Sun, annual motion, 7 ; bulk and mass,
37 ; chromosphere or sierra, 60, 129;
corona, 60, 131, 176 ; daily motion,
6 ; diameter, 35 ; distance, 32 ; ele-
ments in, 129; faculae and flocculi,
127, 130; flames, 59, 130, 176; inte-
rior, 125, 134 ; photosphere or visible
surface, 59, 126; prominences or
solar flames, 59, 130, 176; radiant
energy, 133 ; -reversing layer, 129;
rotation, 129; spots, 127
INDEX
313
Suns, colliding, 110, 206, 237
Superficial appearances, 1
TELESCOPE MOUNTINGS, alt-azimuth,
153; equatorial, 12, 150; meridian
circle, 152 ; mural circle, 153 ; transit
instrument, 153
Telescopic stars, 83
Tele-spectroscope, 95
Tennyson, Alfred, 110
" Testimony of the Suns," 53, 84, 102,
109, 126, 205, 281, 282
Theophilus, lunar crater, 253
Thomson, Prof., 196
Thomson, James, " The Seasons," 229
Thread, quartz, 75 ; spider's, 74 ; a
strand of, 74
Tidal evolution, 202, 213
Time, difference in, 5, 12
Torsion balance, 38
Trails, star, 13
Transit instrument, 153
Triangulation, 31
Trifid Nebula, 123
Trigonometry, 39
Tycho Brahe, 19
UMBRELLA SPHERES, 4
Universes, outside, 86
Uranus, 66, 69
VARIABLE STARS, 107
Vega, 112
Venerable Bede, 17
Venus, 27, 69
Vernal equinox, 7, 139
Via Lactea, 120
Vibratory theory of substance, 195
Violet light- waves, 73, 91
WEIGHT AND MASS, 36
Wheel, revolving, 75
Winter solstice, 140
Wollaston, 194
YOUNG, PROF. CHARLES A., 131
Yule-tide solstice, 8
ZAZEL, A., ix. 219, 233, 242, 290
Zenith, 5
Zodiac, signs of the, 10, 137
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