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THE EARTH’S BEGINNING
------------------------------------------------------------------------
WORKS BY
SIR ROBERT S. BALL,
M.A., LL.D., F.R.S.
THE STORY OF THE HEAVENS.
With 24 Coloured Plates and Numerous Illustrations. New Edition.
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THE EARTH’S BEGINNING.
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THE STORY OF THE SUN.
With 11 Full Page Coloured and other Plates and Numerous
Illustrations. 7s. 6d.
STAR-LAND.
Being Talks with Young People about the Wonders of the Heavens With
Rembrandt Frontispiece and 94 Illustrations in Text. 7s. 6d.
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[Illustration: AN ENGLISH SUNSET TINGED BY KRAKATOA.
(_From a Drawing made at Chelsea at 4.40 p.m. on Nov. 26th, 1883, by Mr.
W. Ascroft._)]
------------------------------------------------------------------------
THE
EARTH’S BEGINNING
BY
SIR ROBERT S. BALL, M.A., LL.D., F.R.S.
Lowndean Professor of Astronomy and Geometry in the University of
Cambridge,
Author of “Star-Land,” “The Story of the Heavens,”
etc. etc.
WITH FOUR COLOURED PLATES AND
NUMEROUS ILLUSTRATIONS
NEW EDITION
CASSELL AND COMPANY, LIMITED
LONDON, NEW YORK, TORONTO AND MELBOURNE
MCMIX
------------------------------------------------------------------------
First Edition October 1901.
Reprinted December 1901, 1903.
Enlarged Edition 1909.
ALL RIGHTS RESERVED
------------------------------------------------------------------------
FOREWORD
SINCE these lectures were delivered in the Royal Institution of Great
Britain there has been much advance in our knowledge of astronomy. The
simultaneous advance in other sciences allied with astronomy has been,
perhaps, even more remarkable. I am glad to avail myself of the
opportunity afforded by a new issue of “The Earth’s Beginning” to draw
attention to certain recent developments of science which relate in a
very striking way to the subject of this volume, namely, the famous
Nebular Theory of the origin of the solar system. It appears to me that
these recent developments tend to reduce greatly, even if they do not
altogether remove, the chief outstanding difficulty which has hitherto
retarded the acceptance of the Nebular Theory.
I have explained in Chapter VI. those views of Helmholtz which have for
so long provided the received explanation of the maintenance of solar
heat. Calculation shows that if the sun’s heat has been maintained by
the contraction of the primæval nebula—and this was the supposition of
Helmholtz—the orb of day cannot have radiated with its present intensity
for a period much longer than twenty million years.
But from the evidence of geology it must now be admitted that the
existence of our earth, indeed even that part of its existence during
which it has been the abode of life, has endured for a period far in
excess of that which this calculation would allow. It therefore seems to
follow that the theory of Helmholtz does not provide an adequate
explanation of such an amazing phenomenon as the continuance of a
sufficient supply of sunbeams throughout the vast periods demanded by
geological phenomena.
There is another entirely different line of reasoning by which Professor
John Joly has recently taught us the immense antiquity of our earth. His
argument is based upon an estimate of the time that must have elapsed
since the waters of the ocean, which had previously been sustained in
the great vapours of the atmosphere, were deposited in the ocean beds.
When the earth had become sufficiently cool to permit of the vapours now
forming the ocean passing from the gaseous to the liquid form, the
oceans descended from the heavens above to the earth beneath in the form
of _fresh_ water. In the lapse of subsequent ages the sea has become
salt because ordinary river water, which always contains some small
quantity of salt in solution, is continually bearing salt down to the
sea. No doubt water is constantly being abstracted from the sea by
evaporation, but only _fresh_ water is thus removed, so in this cycle of
change the salt in the sea must be gradually accumulating. Thus, day by
day, though no doubt extremely slowly, the sea has been growing more and
more salt.
Professor Joly has made an estimate of the quantity of salt daily added
to the sea by all the rivers of the globe. He has also made an estimate
of the total quantity of salt which is at present contained in the sea.
He has thus the means of forming an estimate of the number of years
necessary for the sea to have become converted from its primæval
freshness to its present saltness. His result is not a little
astonishing. The saltness of the sea could not be accounted for unless
the rivers had been running into the sea for at least a hundred million
years. This period is five times as long as the total period during
which the sun could have been shining if the Helmholtzian view were
correct.
Of course, there are many elements of uncertainty in such a calculation.
We have assumed that the total flow of the rivers is practically
constant, and that our estimate fairly represents the average salinity
of river water. We have also made a large assumption in supposing that
we have accurately estimated the total volume of salt in the oceans. But
taken in conjunction with the geological evidence already referred to,
taken in conjunction with the immense periods of time that have been
required for the evolution of life on the globe by the process of
natural selection, the conclusion arrived at is inevitable. It seems
impossible to doubt that the sun must have been shining and that our
solar system must have existed in practically the same form as it is at
present for periods enormously greater than would have been possible if
the heat of the sun had been sustained by the solar contraction only.
The difficulty here indicated has been not unjustly considered the most
serious difficulty with which the development of modern physical and
astronomical science has been confronted. The time during which the sun
must have lasted, according to the received explanation of the source of
its heat and the time during which the sun has actually lasted, as shown
by the facts of geology, present a wide discrepancy. Science demands
that some reconciliation must be effected, yet how is that to be
accomplished? There is only one possible solution of the problem. It is
obvious that there must have been some vast reserve of heat in the sun
in comparison with which the quantity of heat yielded by the contraction
may be deemed insignificant. Until this new source of solar energy had
been discovered, our knowledge of the physics of the solar system lay
under a reproach, which it was the bounden duty of men of science to
endeavour to remove.
During the last few years lines of research carried on in various
directions have, in a most unexpected manner, thrown much light on the
origin of the sun’s heat, and, indeed, we may now say that the great
difficulty which has for so long troubled us no longer exists in a
serious form.
Recent discoveries show that matter possesses stores of energy which, if
not actually boundless, are enormously in excess of what had been
previously deemed possible. These stores of energy are available for
supplying the heat of the sun, and it is easy to show that they are
amply sufficient to furnish the necessary sunbeams for even the longest
periods during which the claims of geology maintain that the sun must
have been shining.
The researches of Professor Sir J. J. Thomson have shown how corpuscles
of matter are sometimes moving with velocities enormously greater than
those of any celestial body with which astronomy had made us acquainted.
The case of high corpuscular velocity which is most generally known is
that presented by radium, the particles from which are being continually
shot forth in myriads. It is quite true that each of these corpuscles is
excessively small, and it may be useful to give the following
illustration bearing on the subject. Think of a number represented by
unity followed by eighteen cyphers, or more concisely as 10^{18}, and
think of a line a kilometre long. If that line were divided into 10^{18}
parts, each of those parts would represent the diameter of a corpuscle
of radium. If that line were multiplied by 10^{18}, the result would be
a line so long that a ray of light would require a period of no less
than 100,000 years to pass from one end to the other.
These corpuscles of radium are, no doubt, excessively small, but the
velocity with which they are moving is comparable with the velocity of
light. When a material object is moving with a velocity of that
magnitude the energy it contains in virtue of that velocity is indeed
startling. A very small grain of sand would, if moving with the velocity
of light, contain, in virtue of that motion, the equivalent of more heat
than could be produced by the combustion of a ton of the best coal. The
late Dr. W. E. Wilson showed that if an excessively minute percentage of
radium should be found to exist in the sun, it would completely account
for the sustentation of the solar heat, and the Hon. R. Strutt has shown
that the minute quantities of radium which he has proved to exist in
terrestrial rocks would enormously protract the earth’s cooling. These
discoveries have, in fact, completely changed the outlook on the problem
of the sun’s heat, and, though no doubt much has yet to be done before
the whole subject is cleared up, the great difficulty may be regarded as
vanquished. Thus, the discovery of radium, and the wonderful phenomena
associated therewith, has pointed out a possible escape from one of the
gravest difficulties in science.
The most notable fact which emerges from the modern study of the
structure of the heavens is the ever-increasing significance and
importance of the spiral nebulæ. The following pages will have failed in
their object if they have not succeeded in emphasising the fact that the
spiral nebula is, next to a fixed star itself, the most characteristic
type of object in the material universe. With every increase in the
power of the telescope, and with every development of the application of
photography to celestial portraiture, the importance of the spiral
structure in nebulæ becomes of ever-increasing interest.
But I revert to this subject here for the purpose of taking notice of a
suggestive paper by Mr. C. Easton in the “Astrophysical Journal,” Vol.
XII., No. 2, September, 1900, entitled “A New Theory of the Milky Way.”
This paper advances the striking view that the Milky Way is itself a
spiral nebula, and certainly the considerations adduced by Mr. Easton
seem to justify his remarkable conclusion.
It is first to be noticed that the Milky Way extends as an irregular
band completely round the heavens, and that it follows very nearly the
course of a great circle. The curious convolutions of the Milky Way, the
varying star densities of its different parts, would, as shown by Mr.
Easton, be completely accounted for if the Milky Way were a mighty
spiral. We view the ordinary celestial spirals from the outside at an
immense distance in space. We view the Milky Way from a position within
the circuit of the nebula. It has, however, been shown by Mr. Easton
that the centre of the Spiral Nebula is not exactly at the sun. The
centre of the Milky Way is near that superb region of the galaxy which
lies in Cygnus.
Thus, the significance of the spiral structure in the universe becomes
greatly enhanced. The spirals abound in every part of the heavens; they
are placed in every conceivable position and in every possible plane;
they have every range in size from comparatively small objects, whose
destiny is to evolve into a system like our solar system, up to
stupendous objects which include a myriad of such systems. There is now
the further interest that as the sun and the solar system are included
within the Milky Way, and as the Milky Way is a spiral, this earth of
ours is itself at this moment a constituent part of a great spiral.
Finally, I would say that, so far as I have been able to understand the
subject, it appears to me that every advance in our knowledge of the
heavens tends more and more to support the grand outlines of the Nebular
Theory as imagined by Kant and Laplace.
R. S. B.
_May 1, 1909._
------------------------------------------------------------------------
CONTENTS
CHAPTER PAGE
I. —INTRODUCTION 1
II. —THE PROBLEM STATED 21
III. —THE FIRE-MIST 39
IV. —NEBULÆ—APPARENT AND REAL 52
V. —THE HEAT OF THE SUN 75
VI. —HOW THE SUN’S HEAT IS MAINTAINED 95
VII. —THE HISTORY OF THE SUN 112
VIII. —THE EARTH’S BEGINNING 122
IX. —EARTHQUAKES AND VOLCANOES 158
X. —SPIRAL AND PLANETARY NEBULÆ 191
XI. —THE UNERRING GUIDE 207
XII. —THE EVOLUTION OF THE SOLAR SYSTEM 246
XIII. —THE UNITY OF MATERIAL IN THE HEAVENS 261
AND THE EARTH
XIV. —THE FIRST CONCORD 294
XV. —THE SECOND CONCORD 308
XVI. —THE THIRD CONCORD 324
XVII. —OBJECTIONS TO THE NEBULAR THEORY 337
XVIII. —THE BEGINNING OF THE NEBULA 348
XIX. —CONCLUDING CHAPTER 361
APPENDICES 369
INDEX 382
------------------------------------------------------------------------
LIST OF ILLUSTRATIONS
FIG. PAGE
An English Sunset tinged by Krakatoa _Frontispiece_
(colour)
1. Immanuel Kant (from an old print) 7
2. A Faint Diffused Nebulosity 17
3. The Crab Nebula 19
4. Jupiter 25
5. Nebulous Region and Star-cluster 33
6. The Great Nebula in Orion 41
7. The Dumb-bell Nebula 45
8. The Crossley Reflector 49
9. The Cluster in Hercules 53
10. Spectra of the Sun and Capella 62
11. Spectrum of Nebula in Orion and Spectrum 64
of White Star
12. Solar Spectra with Bright Lines and Dark 69
Lines during Eclipse
13. The Nebulæ in the Pleiades 71
14. The Sun 81
15. I. Spectrum of the Sun. II. Spectrum of 85
Arcturus
16. Brooks’ Comet and Meteor Trail 89
17. Argus and the surrounding Stars and 103
Nebulosity
18. Trifid Nebula in Sagittarius 105
19. To illustrate the History of the Sun 113
20. Solar Corona 117
21. The Great Comet of 1882 119
22. Special Thermometer for use in Deep 129
Borings
23. At the Bottom of the Great Bore 140
24. Three consecutive Shells of the Earth’s 145
Crust
25. Earthquake Routes from Japan to the Isle 171
of Wight
Showing Localities of Earthquakes 175
(colour)
26. Showing Coasts invaded by the Great 179
Sea-waves from Krakatoa
The Early Stage of the Eruption of 180
Krakatoa (colour)
27. Spread of the Air-wave from Krakatoa to 183
the Antipodes
28. The great Spiral Nebula 193
29. How to find the great Spiral Nebula 196
30. A group of Nebulæ 199
31. A Ray Nebula 201
32. Portion of the Milky Way 205
33. A Spiral Nebula seen Edgewise 211
34. A foreshortened Spiral 212
35. Edge-view of a Spiral boldly shown 213
36. To illustrate Moment of Momentum 223
37. Saturn 233
38. The Ring Nebula in Lyra 249
39. Lunar Craters: Hyginus and Albategnius 255
40. A remarkable Spiral 257
41. A clearly-cut Spiral 259
42. The H and K Lines in the Photographic 276
Solar Spectrum
43. Spectrum of Comet showing Carbon Lines 290
The Solar Spectrum (colour) 290
44. Spectrum of the Sun during Eclipse 291
45. A Spiral presented Edgewise 296
46. The Plane of a Planet’s Orbit 298
47. A Right Angle divided into Ten Parts 301
48. Illustration of the Second Concord 309
49. Orbits of the Earth, Eros and Mars 313
50. I. A Natural System. II. An Unnatural 318
System
51. An elongated irregular Nebula 329
52. Two-branched Spiral 345
53. Cluster with Stars of the 17th Magnitude 353
54. Spectrum of Nova Persei (1901) 359
55. The Apteryx: a Wingless Bird of New 365
Zealand
56. Skeleton of the Apteryx, showing 366
Rudimentary Wings
57. Spirals in other Departments of Nature: 367
Foraminifer
58. Ditto ditto Nautilus 367
59. To illustrate a Theorem in the 369
Attraction of Gravitation
60. First Law of Motion exemplifies Constant 375
Moment of Momentum
61. A useful Geometrical Proposition 376
62. Acceleration of Moment of Momentum 376
equals Moment of Force
63. Moment of Momentum unaltered by 380
Collision
------------------------------------------------------------------------
THE EARTH’S BEGINNING.
CHAPTER I.
INTRODUCTION.
The Earth’s Beginning—The Nebular Theory—Many Applications of the
Theory—The Founders of the Doctrine—Kant, Laplace, William Herschel:
Their Different Methods of Work—The Vastness of the
Problem—Voltaire’s Fable—The Oak-Tree—The Method of Studying the
Subject—Inadequacy of our Time Conceptions.
I TRY in these lectures to give some account of an exceptionally great
subject—a subject, I ought rather to say, of sublime magnificence. It
may, I believe, be affirmed without exaggeration that the theme which is
to occupy our attention represents the most daring height to which the
human intellect has ever ventured to soar in its efforts to understand
the great operations of Nature. The earth’s beginning relates to
phenomena of such magnitude and importance that the temporary concerns
which usually engage our thoughts must be forgotten in its presence. Our
personal affairs, the affairs of the nation, and of the empire—indeed,
of all nations and of all empires—nay, even all human affairs, past,
present, and to come, shrink into utter insignificance when we are to
consider the majestic subject of the evolution of that solar system of
which our earth forms a part. We shall obtain a glimpse of what that
evolution has been in the mighty chapter of the book of Nature on which
we are now to enter.
The nebular theory discloses the beginning of this earth itself. It
points out the marvellous process by which from original chaos the firm
globe on which we stand was gradually evolved. It shows how the
foundations of this solid earth have been laid, and how it is that we
have land to tread on and air to breathe. But the subject has a scope
far wider than merely in its relation to our earth. The nebular theory
accounts for the beginning of that great and glorious orb the sun, which
presides over the system of revolving planets, guides them in their
paths, illuminates them with its light, and stimulates the activities of
their inhabitants with its genial warmth. The nebular theory explains
how it comes about that the sun still continues in these latter days to
shine with the brilliance and warmth that it had throughout the past
ages of human history and the vastly greater periods of geological time.
Then, as another supreme achievement, it discloses the origin of the
planets which accompany the sun, and shows how they have come to run
their mighty courses; and it tells us how revolving satellites have been
associated with the planets. The nebular theory has, indeed, a
remarkable relation to all objects belonging to that wonderful scheme
which we call the solar system.
It should also be noticed that the nebular theory often brings facts of
the most diverse character into striking apposition. As it accounts for
the continued maintenance of the solar radiation, so it also accounts
for that beneficent rotation by which each continent, after the
enjoyment of a day under the invigorating rays of the sun, passes in due
alternation into the repose of night. The nebular theory is ready with
an explanation of the marvellous structure revealed in the rings of
Saturn, and it shows at the same time how the volcanoes of the moon
acquired their past phenomenal activity, and why, after ages of
activity, they have now at last become extinct. With equal versatility
the nebular theory will explain why a collier experiences increasing
heat as he descends the coalpit, and why the planet Jupiter is marked
with those belts which have so much interest for the astronomer. The
nebular theory offers an immediate explanation of the earthquake which
wrought such awful destruction at Lisbon, while it also points out the
cause of that healing warmth of the waters at Bath. Above all, the
nebular theory explains that peerless discovery of cosmical chemistry
which declares that those particular elements of which the sun is
composed are no other than the elements which form the earth beneath our
feet.
When a doctrine of such transcendent importance is proposed for our
acceptance, it is fitting that we should look, in the first instance, to
the source from which the doctrine has emanated. It would already have
made good its claim to most careful hearing, though not perhaps to
necessary acceptance, if it came to us bearing credentials which prove
it to be the outcome of the thought and research of one endowed with the
highest order of intellect. If the nebular theory had been propounded by
only a single great leader of thought, the sublimity of the subject with
which it deals would have compelled the attention of those who love to
study the book of Nature. If it had appeared that a second investigator,
also famous for the loftiest intellectual achievement, had given to the
nebular theory the sanction of his name, a very much stronger claim for
its consideration would at once have been established. If it should
further appear that yet a third philosopher, a man who was also an
intellectual giant, had been conducted to somewhat similar conclusions,
we should admit, I need hardly say, that the argument had been presented
with still further force. It may also be observed that there might even
be certain conditions in the work of the three philosophers which would
make for additional strength in the cause advocated; if it should be
found that each of the great men of science had arrived at the same
conclusion irrespective of the others, and, indeed, in total ignorance
of the line of thought which his illustrious compeers were pursuing,
this would, of course, be in itself a corroboration. If, finally, the
methods of research adopted by these investigators had been wholly
different, although converging to the establishment of the theory, then
even the most sceptical might be disposed to concede the startling claim
which the theory made upon his reason and his imagination.
All the conditions that I have assumed have been fulfilled in the
presentation of the nebular theory to the scientific world. It would not
be possible to point to three names more eminent in their respective
branches of knowledge than those of Kant, Laplace, and William Herschel.
Kant occupies a unique position by the profundity and breadth of his
philosophical studies; Laplace applied the great discoveries of Newton
to the investigation of the movements of the heavenly bodies, publishing
the results in his immortal work, _Mécanique Céleste_; Herschel has been
the greatest and the most original observer of the heavens since the
telescope was invented. It is not a little remarkable that the great
philosopher from his profound meditation, the great mathematician from a
life devoted to calculations about the laws of Nature, the great
observer from sounding the depths of the firmament, should each in the
pursuit of his own line of work have been led to believe that the grand
course of Nature is essentially expressed by the nebular theory. There
have been differences of detail in the three theories; indeed, there
have been differences in points which are by no means unimportant. This
was unavoidable in the case of workers along lines so distinct, and of a
subject where many of the elements were still unknown, as indeed many
are still. Even at the present day no man can give a complete account of
what has happened in the great evolution. But the monumental fact
remains that these three most sagacious men of science, whose lives were
devoted to the pursuit of knowledge, each approaching the subject from
his own direction, each pursuing his course in ignorance of what the
others were doing, were substantially led to the same result. The
progress of knowledge since the time when these great men lived has
confirmed, in ways which we shall endeavour to set forth, the sublime
doctrine to which their genius had conducted them.
Immanuel Kant, whose grandfather was a Scotsman, was born in 1724 at
Königsberg, where his life was spent as a professor in the University,
and where he died in 1804. In the announcement of the application of the
principle of evolution to the solar system, Laplace was preceded by this
great German philosopher. The profound thinker who expounded the famous
doctrine of time and space did not disdain to allow his attention to be
also occupied with things more material than the subtleties of
metaphysical investigation. As a natural philosopher Kant was much in
advance of his time. His speculations on questions relating to the
operations in progress in the material universe are in remarkable
conformity with what is now accepted as the result of modern
investigation. Kant outlined with a firmness inspired by genius that
nebular theory to which Laplace subsequently and independently gave a
more definite form, and which now bears his name.
Kant’s famous work with which we are now concerned appeared in 1755.[1]
In it he laid down the immortal principle of the nebular theory. The
greatness of this book is acknowledged by all who have read it, and
notwithstanding that the progress of knowledge has made it obvious that
many of the statements it contains must now receive modification, Kant’s
work contains the essential principle affirming that the earth, the sun,
the planets, and all the bodies now forming the solar system did really
originate from a vast contracting nebula. In later years Kant’s
attention was diverted from these physical questions to that profound
system of philosophy with which his name is chiefly associated. The
nebular theory is therefore to be regarded as incidental to Kant’s great
lifework rather than as forming a very large and important part of it.
Footnote 1:
We are now fortunately able to refer the English reader to the work of
Professor W. Hastie, D.D., entitled “Kant’s Cosmogony,” Glasgow, 1900.
Kant’s most interesting career is charmingly described in De Quincey’s
“Last Days of Immanuel Kant.”
[Illustration: IMMANUEL KANT.
(_From an old Print._)]
At the close of the last century, while France was in the throes of the
Revolution, a school of French mathematicians was engaged in the
accomplishment of a task which marked an epoch in the history of human
thought. Foremost among the mathematicians who devoted their energies to
the discussion of the great problems of the universe was the illustrious
Laplace. As a personal friend of Napoleon, Laplace received marked
distinction from the Emperor, who was himself enough of a mathematician
to be able to estimate at their true value the magnificent results to
which Laplace was conducted.
It was at the commencement of Kant’s career, and before his great
lifework in metaphysics was undertaken, that he was led to his nebular
theory of the solar system. In the case of Laplace, on the other hand,
the nebular theory was not advanced until the close of the great work of
his life. The _Mécanique Céleste_ had been written, and the fame of its
author had been established for all time; and then in a few pages of a
subsequent volume, called the _Système du Monde_, he laid down his
famous nebular theory. In that small space he gave a wonderful outline
of the history of the solar system. He had not read that history in any
books or manuscripts; he had not learned it from any ancient
inscriptions; he had taken it direct from the great book of Nature.
Influenced by the caution so characteristic of one whose life had been
devoted entirely to the pursuit of the most accurate of all the
sciences, Laplace accompanied his announcement of the nebular theory
with becoming words of warning. The great philosopher pointed out that
there are two methods of discovering the truths of astronomy. Some
truths may be discovered by observing the heavenly bodies with
telescopes, by measuring with every care their dimensions and their
positions, and by following their movements with assiduous watchfulness.
But there is another totally different method which has enabled many
remarkable discoveries to be made in astronomy; for discoveries may be
made by mathematical calculations which have as their basis the
numerical facts obtained by actual observation. This mathematical method
often yields results far more profound than any which can be obtained by
the astronomer’s telescope. The pen of the mathematician is indeed an
instrument which sometimes anticipates revelations that are subsequently
confirmed by actual observation. It is an instrument which frequently
performs the highly useful task of checking the deductions that might
too hastily be drawn from telescopic observations. It is an instrument
the scope of whose discoveries embraces regions immeasurably beyond the
reach of the greatest telescope. The pen of the mathematician can give
us information as to events which took place long before telescopes came
into existence—nay, even unnumbered ages prior to the advent of man on
this earth.
Laplace was careful to say that the nebular theory which he sketched
must necessarily be judged by a standard different from that which we
apply to astronomical truths revealed by telescopic observation or
ascertained by actual calculation. The nebular theory, said the great
French mathematician, has to be received with caution, inasmuch as from
the nature of the case it cannot be verified by observation, nor does it
admit of proof possessing mathematical certainty.
A large part of these lectures will be devoted to the evidence bearing
upon this famous doctrine. Let it suffice here to remark that the
quantity of evidence now available is vastly greater than it was a
hundred years ago, and furthermore, that there are lines of evidence
which can now be followed which were wholly undreamt of in the days of
Kant and Laplace. The particular canons laid down by Laplace, to which
we have just referred, are perhaps not regarded as so absolutely binding
in modern days. If we were to reject belief in everything which cannot
be proved either by the testimony of actual eye-witnesses or by strict
mathematical deductions, it would, I fear, fare badly with not a few
great departments of modern science. It will not be necessary to do more
at present than just to mention, in illustration of this, the great
doctrine of the evolution of life, which accounts for the existing races
of plants and animals, including even man himself. I need hardly say
that the Darwinian theory, which claims that man has come by lineal
descent from animals of a lower type, admits of no proof by mathematics;
it receives assuredly no direct testimony from eye witnesses; and yet
the fact that man has so descended is, I suppose, now almost universally
admitted.
In the case of the great German philosopher, as well as in the case of
the great French mathematician, the enunciation and the promulgation of
their nebular theories were merely incidental to the important
scientific undertakings with which their respective lives were mainly
occupied. The relation of the nebular theory to the main lifework of the
third philosopher I have named, has been somewhat different. When
William Herschel constructed the telescopes with which, in conjunction
with his illustrious sister, he conducted his long night-watches, he
discovered thousands of new nebulæ; he may, in fact, be said to have
created nebular astronomy as we now know it. Ever meditating on the
objects which his telescopes brought to light, ever striving to sound
the mysteries of the universe, Herschel perceived that between a nebula
which was merely a diffused stain of light on the sky, and an object
which was hardly distinguishable from a star with a slight haze around
it, every intermediate grade could be found. In this way he was led to
the splendid discovery which announced the gradual transformation of
nebulæ into stars. We have already noted how the profound mathematician
was conducted to a view of the origin of the solar system which was
substantially identical with that which had been arrived at by the
consummate metaphysician. The interest is greatly increased when we find
that similar conclusions were drawn independently from the telescopic
work of the most diligent and most famous astronomical observer who has
ever lived. Not from abstract speculation like Kant, not from
mathematical suggestion like Laplace, but from accurate and laborious
study of the heavens was the great William Herschel led to the
conception of the nebular theory of evolution.
That three different men of science, approaching the study of perhaps
the greatest problem which Nature offers us from points of view so
fundamentally different, should have been led substantially to the same
result, is a remarkable incident in the history of knowledge. Surely the
theory introduced under such auspices and sustained by such a weight of
testimony has the very strongest claim on our attention and respect.
In the discussion on which we are about to enter in these lectures we
must often be prepared to make a special effort of the imagination to
help us to realise how greatly the scale of the operations on which the
attention is fixed transcends that of the phenomena with which our
ordinary affairs are concerned. Our eyes can explore a region of space
which, however vast, must still be only infinitesimal in comparison with
the extent of space itself. Notwithstanding all that telescopes can do
for us, our knowledge of the universe must be necessarily restricted to
a mere speck in space, a speck which bears to the whole of space a ratio
less—we might perhaps say infinitely less—than that which the area of a
single daisy bears to the area of the continent where that daisy blooms.
But we need not repine at this limitation; a whole life devoted to the
study of a daisy would not be long enough to explore all the mysteries
of its life. In like manner the duration of the human race would not be
long enough to explore adequately even that small part of space which is
submitted for our examination.
But it is not merely the necessary limits of our senses which restrict
our opportunities for the study of the great phenomena of the universe.
Man’s life is too short for the purpose. That our days are but a span is
the commonplace of the preacher. But it is a commonplace specially
brought home to us in the study of the nebular theory. A man of
fourscore will allude to his life as a long one, and no doubt it may be
considered long in relation to the ordinary affairs of our abode on
earth; but what is a period of eighty years in the history of the
formation of a solar system in the great laboratory of the universe?
Such a period then seems to be but a trifle—it is nothing. Eighty years
may be long enough to witness the growth of children and grandchildren;
but it is too short for a single heartbeat in the great life of Nature.
Even the longest lifetime is far too brief to witness a perceptible
advance in the grand transformation. The periods of time demanded in the
great evolution shadowed forth by the nebular theory utterly transcend
our ordinary notions of chronology. The dates at which supreme events
occurred in the celestial evolution are immeasurably more remote than
any other dates which we are ever called upon to consider in other
departments of science. The time of the story on which we are to be
engaged is earlier, far earlier, than any date we have ever learned at
school, or have ever forgotten since. The incidents of that period took
place long before any date was written in figures—earlier than any of
those very ancient dates which the geologists indicate not by figures
indeed, but by creatures whose remains imbedded in the rocks suffice to
give a character to the period referred to. The geologist will specify
one epoch as that in which the fossilized bone of some huge extinct
reptile was part of a living animal; he may specify another by the
statement that the shell of some beautiful ammonite was then inhabited
by a living form which swam in the warm primæval seas. The date of our
story has at least this much certainty: that it is prior—immeasurably
prior—to the time when that marvellous thing which we call life first
came into being.
Voltaire has an instructive fable which I cannot resist repeating. It
will serve, at all events, to bring before us the way in which the lapse
of time ought to be regarded by one who desires to view the great
operations of Nature in their proper proportions. He tells how an
inhabitant of the star Sirius went forth on a voyage of exploration
through the remote depths of space. In the course of his travels he
visited many other worlds, and at length reached Saturn, that majestic
orb, which revolved upon the frontier of the solar system, as then
known. Alighting on the ringed globe for rest and investigation, the
Sirian wanderer, in quest of knowledge, was successful in obtaining an
interview with a stately inhabitant of Saturn who enjoyed the reputation
of exceptional learning and wisdom. The Sirian hoped to have some
improving conversation with this sage who dwelt on a globe so utterly
unlike his own, and who had such opportunities of studying the majestic
processes of Nature in remote parts of the universe. He thought perhaps
they might be able to compare instructive notes about the constitution
of the suns and systems in their respective neighbourhoods. The visitor
accordingly prattled away gaily. He opened all his little store of
knowledge about the Milky Way, about the Great Bear, and about the great
Nebula in Orion; and then pausing, he asked what the Saturnian had to
communicate in reply. But the philosopher remained silent. Eagerly
pressed to make some response, the grave student who dwelt on the
frontier globe at last said in effect: “Sirian, I can tell you but
little of Nature. I can tell you indeed nothing that is really worthy of
the great theme which Nature proposes; for the grand operations of
Nature are very slow; they are so slow that the great transformations in
progress around us would have to be watched for a very long time before
they could be properly understood. To observe Nature so as to perceive
what is really happening, it would be necessary to have a long life; but
the lives of the inhabitants of Saturn are not long; none of us ever
lives more than fifteen thousand years.”
Change is the order of Nature. Many changes no doubt take place rapidly,
but the great changes by which the system has been wrought into its
present form, those profound changes which have produced results of the
greatest magnificence in celestial architecture are extremely slow. We
should make a huge mistake if we imagined that changes—even immense
changes—are not in progress, merely because our brief day is too short a
period wherein to perceive them.
On the village green stands an oak-tree, a veteran which some say dates
from the time of William the Conqueror, but which all agree must
certainly have been a magnificent piece of timber in the days of Queen
Elizabeth. The children play under that tree just as their parents and
their grandparents did before them. A year, a few years, even a
lifetime, may show no appreciable changes in a tree of such age and
stature. Its girth does not perceptibly increase in such a period. But
suppose that a butterfly whose life lasts but a day or two were to pass
his little span in and about this venerable oak. He would not be able to
perceive any changes in the tree during the insignificant period over
which his little life extended. Not alone the mighty trunk and the
branches, but even the very foliage itself would seem essentially the
same in the minutes of the butterfly’s extreme old age as they did in
the time of his life’s meridian or at the earliest moment of his youth.
To the observations of a spectator who viewed it under such ephemeral
conditions the oak-tree would appear steadfast, and might incautiously
be deemed eternal. If the butterfly could reflect on the subject, he
might perhaps argue that there could not be any change in progress in
the oak-tree, because although he had observed it carefully all his life
he could not detect any certain alteration. He might therefore not
improbably draw the preposterous conclusion that the oak-tree must
always have been just as large and just as green as he had invariably
known it; and he might also infer that just as the oak-tree is now, so
will it remain for all time.
[Illustration: Fig. 2.—A FAINT DIFFUSED NEBULOSITY (n.g.c. 1499; in
Perseus).
(_Photographed by Dr. Isaac Roberts, F.R.S._)]
In our study of the heavens we must strive to avoid inferences so
utterly fallacious as these which I have here tried to illustrate. Let
it be granted that to our superficial view the sun and the moon, the
stars and the constellations present features which appear to us as
eternal as the bole of the oak seemed to the butterfly. But though the
sun may seem to us always of the same size and always of the same
lustre, it would be quite wrong to infer that the lustre and size of the
sun are in truth unchanging. The sun is no more unchanging than the
oak-tree is eternal. The sun and the earth, no less than the other
bodies of the universe, are in process of a transformation no less
astonishing than that wonderful transformation which in the course of
centuries develops an acorn into the giant of the forest. We could not
indeed with propriety apply to the great transformation of the sun the
particular word growth; the character of the solar transformation cannot
be so described. The oak-tree, of course, enlarges with its years, while
the sun, on the other hand, is becoming smaller. The resemblance between
the sun and the oak-tree extends no further than that a transformation
is taking place in each. The rate at which each transformation is
effected is but slow; the growth of the oak is too slow to be perceived
in a day or two; the contraction of the sun is too slow to be
appreciable within the centuries of human history.
Whatever the butterfly’s observation might have suggested with regard to
the eternity of the oak, we know there was a time when that oak-tree was
not, and we know that a time will come when that oak-tree will no longer
be. In like manner we know there was a time when the solar system was
utterly different from the solar system as we see it now; and we know
that a time will come when the solar system will be utterly different
from that which we see at present. The mightiest changes are most
certainly in progress around us. We must not deem them non-existent,
merely because they elude our scrutiny, for our senses may not be quick
enough to perceive the small extent of some of these changes within our
limited period of observation. The intellect in such a case confers on
man a power of surveying Nature with a penetration immeasurably beyond
that afforded by his organs of sense.
[Illustration: Fig. 3.—THE CRAB NEBULA (n.g.c. 1952; in Taurus).
(_Photographed by Dr. Isaac Roberts, F.R.S_)]
That the great oak-tree which has lived for centuries sprang from an
acorn no one can doubt; but what is the evidence on which we believe
this to have been the origin of a veteran of the forest when history and
tradition are both silent? In the absence of authentic documents to
trace the growth of that oak-tree from the beginning, how do we know
that it sprouted from an acorn? The only reason we have for believing
that the oak-tree has gone through this remarkable development is
deduced from the observation of other oak-trees. We know the acorn that
has just sprouted; we know the young sapling as thick as a walking
stick; we know the vigorous young tree as stout as a man’s arm or as his
body; we know the tree when it first approaches the dignity of being
called timber; we can therefore observe different trees grade by grade
in a continuous succession from the acorn to the monarch of five
centuries. No one doubts for a moment that the growth as witnessed in
the stages exhibited by several different trees, gives a substantially
accurate picture of the development of any individual tree. Such is the
nature of one of the arguments which we apply to the great problem
before us. We are to study what the solar system has been in the course
of its history by the stages which we witness at the present moment in
the evolution of other systems throughout the universe. We cannot indeed
read the history in time, but we can read it in space.
The mighty transformation through which the solar system has passed, and
is even now at this moment passing, cannot be actually beheld by us poor
creatures of a day. It might perhaps be surveyed by beings whose pulses
counted centuries, as our pulses count seconds, by beings whose minutes
lasted longer than the dynasties of human history, by beings to whom a
year was comparable with the period since the earth was young, and since
life began to move in the waters.
May I, with all reverence, try to attune our thoughts to the time
conceptions required in this mighty theme by quoting those noble lines
of the hymn—
“A thousand ages in Thy sight
Are like an evening gone,
Short as the watch that ends the night,
Before the rising sun.”
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