/TlRKElSY
I HBRARY
UNivat&iTYOf
W. F, STANLEY,
CUMBERLOW,
SOUTH NORWOOD,
NOTES
ON THE
NEBULAR THEORY
IN RELATION TO
STELLAR, SOLAR, PLANETARY, COMETARY,
AND GEOLOGICAL PHENOMENA.
BY
WILLIAM FORD STANLEY,
F.E.A.S., F.G.S., RE.MET.SOC., M.PnYs.Soc.,
AUTHOR OF TKEATISES ON THE " PROPERTIES AND MOTION OF FLUIDS,"
" SURVEYING INSTRUMENTS," " DRAWING INSTRUMENTS," ETC.
" A cause qu'il ne convient pas si bien a la souveraine perfection qui est en
Dieu de le faire auteur de la confusion que de 1'ordre, et aussi que la notion
que nous en avons est moins distincte, j'ay cru devoir icy preferer la proportion
et 1'ordre a la confusion du Chaos." Descartes.
LONDON:
KEGAN PAUL, TRENCH, TRUBNER & CO., LTD.
1895.
ALEBE V JXAMMAM.
FEINTED BY TAYLOR AND FRANCIS,
RED LION COURT, FLEET STREET.
LOAN STACK
PREFACE.
THE subject of the following pages as a study commenced
to fascinate me in my youth, when, deeply imbued with
the study of Newton, I was trying vainly to unravel the
theoretical possibilities of the original structure of the
marvellous mechanism of the universe. It has been ever
present with me throughout a busy life and has been
often reconsidered, leading me to the conclusion that a
modified form of the Nebular Theory of Laplace might
be established on some new ideas which I formed and by
certain calculations that I felt sure the actual conditions
warranted. These speculations are now offered to the
scientific world for approval.
I arranged this matter as it presented itself to my mind
originally in papers upon separate parts of the subject, as
a less confident mode of introduction ; but I was advised by
orthodox authorities that such papers were too speculative
to communicate to the learned societies that I thought
at the time best adapted for their consideration. These
papers, which I now edit in abstract, have been put aside
62
941
iv PREFACE.
for many years. Upon the permissible borders of the subject
I read a paper before the Geologists' Association in March
1883, " Upon the Causes of the Elevation and Depression
of the Earth's Surface," which I considered to represent
the continuity of effects of nebular conditions upon the
Earth (reported in l Nature,' March 29th, 1883). Some
of the speculative unpublished matter of this paper is in-
cluded in the following pages, with copies of my diagrams.
I wrote a paper in 1878 upon " Some Hypothetical
Conditions of the Properties and Motions of Comets," that
I assume to depend upon original nebular conditions, which,
after some correspondence with a high authority, I sent to
the l English Mechanic/ a journal in which astronomical
subjects are frequently discussed (published 22nd June,
1883). This matter is incorporated herein with some con-
clusions arrived at after further consideration of the subject.
At the British Association in 1883 I read a paper entitled
" Notes upon the Rotation-period of the Earth and Revo-
lution-period of the Moon, deduced from the Nebular
Hypothesis of Laplace" (Brit. Assoc. Reports, 1885, p. 915).
The subject of this paper is more fully treated in the
present work.
I also read a paper before the Geological Society showing
the error in Mallet's theory of the contraction of the Earth
in cooling, which process was assumed to produce the
PREFACE. V
great elevation and inclination of strata observed in nature
(Phil. Trans, vol. clxiii. part 1). This theory, which has
been very generally accepted, derived most of its support,
I think, from a large accidental error which I was able to
point out in the mathematical calculations (Proc. Geol. Soc.
June 1884), so that the causes of elevation and inclination of
strata discussed herein as a process of the continuity of
nebular conditions may be said to remain unexplained by
any hypothesis founded upon correct data.
'J ifcriffi yyjj.t [jjnigno w> 80bi *j; nolhoqtnq r?i ( 3ds(tf#fi
I have also read several papers before the British Asso-
ciation and the Geological Society contravening some points
in the popular theory of a universal glacial age, which I
think was only local at any period, and is opposed to the
Nebular Theory, which I thought, at the time I wrote the
papers, demanded a uniform decrement of heat in time
in the entire cosmic system. This idea as regards the
periodic amount of solar radiation to the Earth I have
somewhat modified in these pages by considering the effects
of critical temperatures upon the solar nebula ; but as I
have endeavoured to bring the whole subject together as
briefly as possible as it presents itself to my mind, it is
unnecessary to discuss more particularly what I have
already attempted to do in this direction. The greater
part of this matter has remained unpublished, except partly
in short abstracts, being at present somewhat out of concord
with prevailing theories.
VI PREFACE.
What 1 most regret in this matter is that I am unable
to fully discuss many theoretical ideas that have been pro-
posed by scientific men without extending this sketch very
much beyond the limit necessary for the brief statement of
my own ideas. This is unfortunate, as I find in reading
up the subject, for the most part since I wrote these pages,
that other ideas approach my own in a few particulars.
One feels also that, in the discussion of a speculative
subject, in proportion as ideas are original they must be
difficult to correlate with the more or less established scientific
theories. The whole subject, however, is undoubtedly in a
tentative state, and must be studied generally upon a broader
and more exact basis in detail than it has heretofore been,
if a satisfactory theory is to be established. For this inves-
tigation some acceptable data must be found before refined
mathematical analysis can be of much value. For this
theory I can only hope I have put forward some available
suggestions.
I am indebted to Mr. W. T. Lynn, B.A., F.R.A.S., for
critical examination of my proofs both for reading and for
calculations. I am indebted to the kindness of Mr. William
Crookes, F.R.S., and Professor G. F. Fitzgerald, F.R.S.,
for some suggestions which have enabled me to render the
matter in the second and twelfth chapters more definite and
logical. I am indebted to an eminent practical geologist,
who withholds his name, for reading and suggestion in
PREFACE. v
Chapters X. to XVI. ; to Mr. Charles Kirk for care in
the reproduction of the Plates ; and to Mr. W. Francis, of
my printers' firm, for care in correcting my proofs.
South Norwood, March 1895.
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CONTENTS-INDEX.
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INTRODUCTION. HISTORICAL NOTES : Ancient Ideas Re-
naissance, p. 2. Descartes Wright, p. 3. Kant, p. 4.
Lambert Sir Wm. Herschel, p. 6. Laplace, p. 7.
Mayer, p. 9. Helmholtz, p. 10. Lane Faye, p. 11.
Projectile Theory Limits of Theory to be discussed,
p. 15.
\Tl tt Tl T^T t TT *'\
1
CHAPTER II.
CONDITIONS OF MATTER POSSIBLY ACTIVE IN THE CONDENSA-
TION OF AN EXTENSIVE S STSTEM OF COSMIC NEBULA :
Time and Space, p. 17. Original State of Matter, p. 18.
Separation of Systems of Original Matter, p. 19. Com-
parison with Astronomical Nebulae, p. 20. Tenuity of
Original Matter, p. 21. Milky Way Atomic Theory,
p. 22. Sir Benj. Brodie's Theory of Original Matter,
p. 23. Suggestions for the Constitution of the Nebulae
Pneuma, p. 23. Lockyer's Dissociation Crookes's
Fractionation, p. 25. Pneumites, p. 26. Chemical
Action in a Pneuma System, p. 30. Cohesion of Matter,
p. 32. Observation of Astronomical Nebulae, p. 35.
Condition of the Sun, p. 36.
CHAPTER III.
FORMATION OF STELLAR AND SOLAR SYSTEMS : Formation
of Nebulae from the original Pneuma System, p. 38.
Suggested Motive Conditions in the original Pneuma,
p. 40. Cyclone-inducing Conditions, p. 42. Formation
of Spiral Nebular Systems, p. 45. Solar-Planetary
inducing conditions in Nebulae, p. 46. Permanency of
Stellar Systems, p. 47. Distances under which Gravita-
tion may be active Action of Gravity in formation of
Circular Orbits, p. 49.
CHAPTER IV.
STELLAR AND SOLAR CONDENSATION. FORMATION OF ORBITS :
Separate Stellar and Solar- Planetary inducing con-
ditions according to amount of Rotation, p. 52. Limits
of a Solar-Planetary-Cometary System, p. 53. Action
of Gravity on distant Condensations, p. 55. Condensation
to a Solar Centre, p. 56. Direction of Approach to the
Sun of exterior Matter Formation of Orbits, p. 58.
Cometary Orbits, p. 60. Formation of a Planetary
Plane, p. 62. Planets formed at the Perihelion of
Cometary Orbits, p. 63.
CHAPTER V.
DISCUSSION OF THE MECHANICAL PRINCIPLES UPON WHICH
OUR SOLAR-PLANETARY SYSTEM MAY HAVE BEEN FORMED.
DEMONSTRATION OF THE THEORY OF LAPLACE, WITH
SOME MODIFICATIONS. LIMITS OF A COMETARY SYSTEM:
Energy of the Solar System Its Asymmetry, p. 65.
Scheme of a Symmetrical Gaseous Solar-Planetary
System, p. 67. Modes of Condensation of Interior
Planets in a Spheroidal Nebular System, p. 71. Mode
of Condensation of Extreme Outer Solar Nebula,
p. 72. Breaking-up of Gaseous Zone-Systems, p. 73.
Influencing Conditions of Planet-formation Critical
Temperatures, p. 74. Some Modifying Conditions, p. 77.
CHAPTER VI.
CERTAIN CONDITIONS IN THE EARLY SOLAR SYSTEM WHICH
MAY BE INFERRED FROM THE DISTANCES AND MASSES OF
THE PLANETS UPON THE NEBULAR THEORY : The Dis-
tances of the Planets from the Sun Bode's Law, p. 80.
Masses of the Planets, p. 81. Proportional Densities,
p. 82. Probable Form of the Original Planetary Nebula,
p. 84. Effects of the voluminous Ring of Jupiter upon
the Intra-Jupiter Solar System, p. 85. Relative Rate of
Cooling of the Intra-Jupiter System with the Earth,
p. 86.
Xll
CHAPTER VII.
SUGGESTIONS FOR CAUSES OF DIRECTION OF ROTATION OF THE
SUN AND PLANETS. THE DIRECTION OF REVOLUTION.
VELOCITY OF ROTATION OF THE PLANETS AND OF THEIR
SATELLITES : Direction of the Solar Axis of Rotation,
p. 88. Direction of the Planets' Axes, p. 89. Rotation
of the Sun, p. 90. Momentum of a Planet, p. 95.
Orbital Velocity of a Planet, p. 96. Rotation of Planets,
p. 97. Calculated Rotation of Jupiter and Saturn,
p. 101. State of Jupiter and Saturn, p. 103. Rotation
of the Asteroids of Mars, p. 106 . Rotation of the Earth,
p. 108.
CHAPTER VIII.
REVOLUTION OF SATELLITES. DIRECT MOTION. RETRO-
GRADE MOTION. COMPARISON OF THE REVOLUTION OF
THE MOON WITH THE ROTATION OF THE EARTH :
Revolution of Satellites with Direct Motion, p. 110.
Calculation of Revolution of the Satellites of Jupiter and
Saturn, p. 111. Satellites of Mars, p. 113. The Moon,
p. 114. Retrograde Motion of Satellites, p. 116.
CHAPTER IX.
COMETS CONSIDERED AS ORDINARY GRAVITATIVE MATTER IN
ROTATION CONSTRUCTIVELY AS A PART OF THE PLANETARY
SYSTEM : Discussion of Principles, p. 121. Comets of
Long Period, p. 125. Comets of Short Period Sym-
metrical Elements of Comet-formation, p. 126, Comets
considered as Gravitative Matter, p. 128. Conditions
Xlll
under which a Comet may be considered as a Planetary
Body, p. 130. Heat Electricity Orbital Momentum,
p. 131. Elongation of the Cometary Mass near Peri-
helion, p. 136. Orbits of the outer parts of a Comet
Focal Point, p. 139. Direction of a Cometary Train in
relation to the Sun, p. 140. Widening Curvature of the
Train by crossing Orbits, 142. Formation of a New
Head to a Comet, p. 144. Some general conditions,
iji>o{o(I 'io Lobt/i .081 .q r gj;*m;-Lflj)J lo
CHAPTER X.
THE EARTH, CONSIDERED IN EVIDENCE OF FORMER NEBULAR
CONDITIONS. ITS INTERNAL FLUIDITY. TIDAL FRIC-
TION. FIGURE DUE TO ROTATION : The Earth con-
sidered as a Model Planet, p. 147. Factors of Earth-
formation, p. 148. From a Gaseous System, p. 149.
From aggregation of Planetoids, p. 150. Internal
Fluidity of the Earth discussed, p. 150. Effects of
Tidal Friction, p. 156. Change of figure due to Rota-
tion-Velocity, p. 157.
J ' F
' CHAPTER XI.
Y3L (ISO "KlDm KOIT&MJIOH-HTH.A2 "50 XOiTIdXoD OTfTOrfl'i^f
SUPERFICIAL CONDITIONS OF THE EARTH DUE TO DISCRETE
CONDENSATIONS, FORMED BETWEEN THE EARTH'S ORI-
GINAL NEBULA-ZONE AND THE ORBIT OF MARS : For-
mation of Land-areas by Inclusion of Planetoids, p. 160.
Projection of a large Intra-Mars Planetoid upon the
Earth, p. 165. Formation of a Continent therefrom,
.81 P- 1"6.
XIV
CHAPTER XII.
HYPOTHESIS OF THE FORMATION OF THE EARTH UNDER
PURELY NEBULAR CONDITIONS : Conditions specialized,
p. 169. Distinct Periods of Deposition Period of
Condensation of highly Refractory Matter, p. 170.
Period of Condensation of Volatile Metals, Oxygen, and
Halogens with Metals and Metalloids, p. 174. Distri-
bution of Land-areas, p. 180. Period of Deposition of
Water, p. 184.
CHAPTER XIII.
CONDITIONS OF THE COOLING EARTH DUE TO FORMATION OF
ICE AT THE POLES : Pre-Glacial and Glacial Period s ;
p. 189. -Distribution of Ice at the Poles, p. 192.
Present Conditions brought about by Deposition of Ice,
p. 193. Where Ice-pressures are most active, p. 197.
Extrusion of Volcanic Matter through Ice-pressures,
p. 199. Pressure of Water and iSteam in Volcanic
Eruptions, p. 201. Notes upon Theories proposed
p. 207.
CHAPTER XIV.
PERIODIC CONDITION OF EARTH-FORMATION PRODUCED BY
THE EFFECTS INCIDENTAL TO THE NEBULAR CLOUDING
AT INFERIOR PLANETARY FORMATION AND AT CRITICAL
TEMPERATURES OF MATTER SURROUNDING THE SUN :
Condition of the Sun during Earth-formation, p. 210.
Distinct Solar-heating Periods, p. 213. Division of
Special Periods, p. 214. General effects of the Large
Nebulous Sun upon Meteorological Conditions, p. 218.
XV
CHAPTER XV.
CONSIDERATION OF TIME ELEMENTS IN THE SOLAR SYSTEM,
PARTICULARLY FOR ESTIMATING THE AGE OF THE EARTH
AND FOR ITS GEOLOGICAL PERIODS : Time of Conden-
sation of the Solar System, p. 220. Calculation of Time
of Condensation for the Nebula extending to the Orbit of
Neptune, p. 222. The same for the Orbit of the Earth,
p. 223. Distribution of Time upon the Earth, through-
out the Varying Periods of Condensation of the Sun
and the Inferior Planets, p. 224. Table in millions of
years Period of the Formation of the Nebulous Earth,
p. 225.
CHAPTER XVI.
GEOLOGICAL PERIODS CORRELATED WITH ASTRONOMICAL PHE-
NOMENA : Discussion of Geological Periods, p. 228.
Archaean Period, p. 231. Archaean Time in Relation
to the Conditions of Animal Life, p. 233. Cambro-
Silurian Period, p. 235. Devonian Period, p. 239.
Permian Period, p. 241. Triassic and Rhaetic Periods
Jurassic Period Cretaceous to Tertiary Periods, p. 243.
Glacial Period, p. 246, Future Period, p. 249.
APPENDICES. A. Hypothesis of Radiation of Heat and Light,
p. 252. B. Mallet's Theory, p. 256. C. Contempo-
raneous Stratification of Rocks of the prevailing Chemical
Elements, p. 258.
NOTES
ON THE
NEBULAR THEORY.
CHAPTER I.
INTRODUCTION. HISTORICAL NOTES. LIMITS OF THE
THEORY TO BE DISCUSSED.
THE origin of the material universe has occupied the deepest
thoughts of many of our most profound thinkers. These
speculations must, however, rest for ever upon the borderland
of Science, where few practical men may care to tread. To
bring this subject more nearly into co-relation with practical
science it is necessary that we keep more nearly to the
evidences of natural phenomena for our data than has here-
tofore been done by our scientists, who have so often in this
matter followed pure speculations only. We may also
possibly with advantage make tests of the theories that have
been proposed by submitting them to calculations taken
directly from the premises offered in the various hypotheses.
To place this matter before the reader clearly for discussion,
it will be convenient to offer a few historical notes on the
leading theories that have been proposed, upon which it is
my purpose to graft certain suggestions and to make certain
B
2 NOTES ON THE NEBULAR THEORY.
calculations. These historical outlines will save space being
taken by constant definitions of the earlier theories, by making
use of references to the paragraph numbers to be found in
this chapter.
1. The ancient ideas of the Kosmos in no way approach
the possible conditions of a Nebular theory the extent of
the universe in early times was conceived to be only that which
appeared evident to the senses, the earth being taken as the
centre of the universe, surrounded and enclosed by firma-
ments that were assumed to be revolving solid constructions,
which were variously defined. To this, however, we have
some exceptions. Anaximines believed stars to be of fiery
substance and to carry invisible earthly bodies with them.
As a preliminary idea of early nebular conditions he held
that air was the original material of the universe, from which
all things were engendered and into which they resolve *.
Pythagoras taught his disciples that the sun was the centre
about which the planets revolved f, by which he accounted
for eclipses and the motions of the planets, and thereby
clearly anticipated what we term the Solar System of Coper-
nicus. This was a great advance upon the prevailing theory,
which was limited to a firmament or a number of crystal
spheres surrounding the earth. The theory of Pythagoras,
probably derived from the Chaldeans, was, however, far too
much in advance of the age to be accepted by the following
generations of popular scholars and theorists, who were, in
many instances, strongly prejudiced against it owing to the
influence of the prevailing superstitions of the time, in
accordance with which alone popularity could be attained.
2. The earliest suggestion of a nebular hypothesis that
occurs within the Kenaissance period is probably that of
Tycho Brahe, who, to account for the new star which appeared
in 1572, suggested that stars were formed by condensation of
* ' History of Philosophy,' T. Stanley, 4th e<L 1743, p. 54.
t Id. p. 444.
HISTORICAL NOTES. O
the ethereal substance of which he imagined the Milky Way
was composed *. Kepler accepted Tycho Brahe's idea, which
he somewhat extended in his account of the new star which
appeared in 1604, by suggesting that the nebular substance
might not be confined to the Milky Way alone but may have
pervaded all space |. In an account of the eclipse of the sun
at Naples in 1605 he suggests that nebular matter is of the
same kind as that which appears around the dark body of the
moon in a total eclipse.
3. Descartes appears to have been the first to attempt to
construct a complete theory of the origin of the known
universe, or to systematize the matter of space. In this he
assumes that universal matter originally existed in three
states coarse, fine, and very attenuated ; that it drifted
originally in a complex system of whirls, and that each of
these whirls formed a solar or planetary system J. This
theory, brought forward again recently by M. Faye, will be
presently discussed : we may term it the Vortex Theory.
4. Thos. Wright was the first to suggest a complete gravi-
tation theory of the universe founded upon astronomical
observations taken accurately enough to be of any scientific
value . He suggests that the universe, represented by the
Milky Way, is a unit gravitation system in general revolu-
tion in the form of a bifurcating stratum composed of all the
visible stars, which resemble our sun. This is now commonly
termed the Grindstone Theory. He estimated the direction
in which our sun is travelling among the stars by discussion
of the parallax. He suggests that the stars, by uniformity
of creation, have revolutionary subsidiary systems of planets
similar to our own solar system. In the plate which forms
* ' Progymnasmata,' 1572, p. 795.
t l Stella nova in pede Serpentarii,' 1606, p. 115.
| ' Essais Philosophiques,' 1637. l Speciminse Philosophic^,' 1644.
' An Original Theory of the Universe/ Thomas Wright, 1750. See
also De Morgan, Phil. Mag. 3 ser. xxxii. p. 241 .
B2
NOTES ON THE NEBULAR THEORY.
our frontispiece he shows by shading the theoretical gravita-
tion influences over matter of our Sun, Sirius, and Higel, in
which each of these star systems is shown extending its
influence over an approximately equal area of space, and
nearly meeting the system of each of the others. He
suggests that with more perfect telescopes the rings of
Saturn will be discovered to be formed of small satellites.
He considers the measurable visible sun to consist of a
vaporous and a nebulous atmosphere, the dense solid or
liquid body of the sun being much smaller than it appears,
possibly only of about two thirds its apparent dimensions.
He contends that the Milky Way forms one vast system
composed of solar systems like our own. He does not appear
to know of more than the six nebulse mentioned by Halley as
"light coming from an extraordinary large space in the ether,
through which a lucid medium is diffused, which shines with
its own proper lustre"*. Wright refers to these cloudy
spots as " condensations of vapour among the mass of stars
to which our sun belongs." Comets are suggested to have
elliptical closed orbits, as represented in the frontispiece, and
therefore to be periodical.
5. Wright's original bold but (as regards particulars left
unnoticed) somewhat indefinite outline was filled up more in
detail by Kant, who fully recognizes the speculations of
" Wright of Durham/' and accepts his general principles
concerning the structure of the universe. Kant's original
speculations given in the second part of his work are princi-
pally directed to account for the formation of the solar
system, the mass and motion of which are assumed to have
been produced by the aggregation of free particles that
were formerly uniformly distributed in space in an attenuated
form. The particles falling together at an early period by
initial gravitation formed masses by local condensations.
* Halley, Phil. Trans. 1714.
HISTORICAL NOTES. 5
These masses, under universal gravitation, are assumed to
have encountered the resistances of other masses and particles,
generally distributed, so that those parts of the system only
could continue to move freely and form concentric systems
which acquired a linear velocity sufficiently in equation with
the nearest centralizing attraction to produce orbital motion.
The matter deflected from the direct line of attraction towards
the sun passed into revolution about it. The revolution pro-
duced a denser extended equatorial plane, into which exterior
matter was drawn whilst approaching the sun. The velocity
of the particle falling towards the sun depended upon the
distance fallen, the direction it finally took upon the sum of
lateral deviations it experienced in consequence of encounters
with other particles, which directed it, under the influence of
gravitation, into the path of least resistance. The particles
which did not meet the conditions of circular or orbital
motion fell into the sun, where his attraction predominated.
The particles deflected or held in equilibrium in nearly the
same orbit formed the planet by gravitating towards denser
condensations of surrounding matter, which, acting under
similar conditions, took the same direction of revolution as
the sun. The same motive principles in matter which pro-
duced the revolution of the planet around the sun also
produced its own rotation and the revolution of its satellites
in the same direction. The planet in regard to rotation is
considered as an independent body. The rotative movement
might therefore, according to the momentum of the mean
drift of its matter, take one direction or the other, the
direction of rotation being due to the unequal velocity of the
particles in circulation around the sun at the time they were
falling upon the new forming planet through its prevailing
local attraction. Saturn is taken as a particular case for
consideration, in which vaporous conditions of condensation
are suggested, the ring being in revolution and thrown off
the planet where the centrifugal force of its matter becomes
O NOTES ON THE NEBULAR THEORY.
in equilibrium with gravitation *. It will be convenient to
denominate the nebular theory of Kant the Discrete System,
in contradistinction to the Concrete or gaseous system of Sir
William Herschel and Laplace, notices of which follow.
It is readily seen that matter equally distributed in space
could not possibly drift in the manner proposed by Kant, but
that it must at an early period fall into the whirl system of
motion proposed by Descartes. M. Faye, although generally
supporting the discrete theory of Kant, has demonstrated
that if matter drifted under the influence of gravitation only,
as proposed by this philosopher, it would possess no rotation
upon condensation in forming the sun or a separate planetary
system t
Lambert followed closely in the theory of Kant, his greatest
divergence being in the division of the universe into many
galactic systems of which our Milky Way represents one
only f. This is now denominated the Island Theory.
6. No further advance was made in the nebular theory
until over 2000 nebulae had been discovered and examined
by Sir William Herschel, an account of which was placed
before the Koyal Society in several papers from 1784 on-
wards. The nebulae were recognized individually as immense
gravitation systems in 1789. The planetary nebulae were
adduced as giving evidences of atmospheres of shining fluid
about stellar foci, which were suggested to be in a state of
condensation in 1791. The entire subject is brought together,
embracing ideas of the origin of our own solar system being
derived from nebular matter, in Phil. Trans. 1811, p. 269 et
seq. The conclusions arrived at are somewhat less original
than Herschel supposed. They possibly mark in one respect
the influence of chemical discovery, in which the smallest
parts of bodies were beginning to be recognized as distinctly
* ' Allgemeine Naturgeschichte und Theorie des Himmels,' 1755.
f ' Sur rOrigine du Monde/ 2nd ed. p. 135.
J l Cosmologische Briefe, ' 1761.
HISTORICAL NOTES. 7
structural units *, all of which might be brought to a gaseous
state by heat : therefore the possibility of the existence of all
known matter in three forms gaseous, liquid, and solid
dependent upon the special temperature to which any element
is exposed. The recognition of a possible gaseous state for
all matter appears to have suppressed for the time the former
prevailing idea, as regards the nebular hypothesis, that
material particles separately distributed in space represented
the most attenuated form of matter. The gaseous element
offered also at the same time a new foundation for the con-
struction of a nebular hypothesis.
7. The subject is taken up by the powerful analytical
mind of Laplace in 1796 f and in 1799, and advanced in
following years J. It is treated entirely de novo, this author
evidently not knowing how much had been thought out in
the same direction by others. He follows without knowing
it closely upon the general arguments of Kant, particularly
those of his theory of the formation of the rings of Saturn,
with the important addition of the introduction of the gaseous
nebular element as a universal medium. He formulates that
whatever could have directed the movements of the planets,
it must have been originally a concrete system embracing
the whole of these bodies, which could not possibly, seeing
its immense extent, have been other than an aerial fluid
surrounding the sun and possessing the same direction of
revolution. To ensure this possible extension of matter he
supposes that the nebulous gaseous matter was of sufficiently
high temperature for all solids to exist in a purely gaseous
state. He suggests that this attenuated matter of the solar
system probably resembled some of the nebulae visible in the
telescope, or more particularly the nebulous stars which were
formed from the general more attenuated and highly heated
* Lavoisier's ' Traite* elSmentaire de Chemie,' 1789.
t * Exposition du Systeme du Monde/ vol. ii. p. 295.
J Id. 3rd edit. 1813
O NOTES ON THE NEBULAR THEORY.
nebulous matter. The original momentum of the solar
nebula in revolution was conserved, so that as it contracted
it attained higher velocity. The planets were formed at the
limits of the solar atmosphere when it was a planetary nebula
by successive zones of vapour being abandoned in the plane
of the sun's nebular equator, at a radius where the centri-
fugal force of the zone, due to its contraction and accelerated
rotation, was in equation with gravity for the orbit of the
planet. After separation the parts of the zone-ring would
maintain the same angular velocity as they had while in
contact with the sun for a time ; but in falling towards the
new planet forming by local condensation, the exterior
matter, besides its excess of linear velocity over interior
parts due to its exterior position, would attain further excess
of velocity through gravity. The downward impulse of
gravitation into tangential velocity would impress an excess
of velocity over the original angular velocity in condensation
upon the planet, and thereby cause its rotation to be in the
same direction as the revolution of the planet around the sun.
This effect will be discussed, with a diagram, in the body of
the work. The satellites were formed at the limits of the
atmosphere of the nebulous planets at an early period in the
same manner as the planets themselves were formed about
the sun. He suggests that comets are of another system
with linked orbits, and that they move under the mutual
attractions of our sun and other separate stars. The theory
of Laplace has many able supporters, among the most able of
whom is the celebrated astronomer M. C. "Wolf*, who has
made important additions to it.
8. The discovery of certain factors of the mechanical
theory of heat by Mayer in 1842 led this philosopher in
1848 to propound a theory of the possibility of the sun's heat
being maintained by the percussion of the fall of meteoric
* ' Les Hypotheses Cosmogoniques,' 1886, p. 35.
HISTORICAL NOTES.
matter upon his surface *, a principle entailing the formation
of the sun from such matter, or what became the " Meteoric
theory of the Sun" This theory, which resembles that of
Buffon, wherein the sun's heat is suggested to be maintained
by the fall of comets constantly upon his surface, was ex-
tended to the formation of the planets also. It was thought
to be supported by the resolution of many presupposed
gaseous nebulas into stars by means of the great reflecting
telescope of Lord Kosse, erected in 1845. These observa-
tions led many astronomers to hold that all nebulas would be
resolvable if sufficient optical power were applied to them,
and, therefore, that we possess no certain inference of the
presence of incandescent gaseous matter in space.
9. Mayer's theory was fully investigated by Lord Kelvin,
and its entire insufficiency to account for the dispensation of
solar heat clearly demonstrated f- It was supported by
Prof. Tait, who extended the conditions by suggesting that
the incandescent state of nebulae which were afterwards
spectroscopically demonstrated as being gaseous matter by
Dr. Huggins, might be derived from collisions of small
cosmical bodies which were surrounded by gaseous atmo-
spheres. Lord Kelvin, in reconsidering the meteoric theory
with this modification, thought that, although the sun might
have been formed by the cohesion of small masses, his heat
could not be maintained by the mechanical collisions of
gravitating matter only. He considers the low rate of
cooling, and the consequent constancy of emission of heat,
as being covered in great part by the high specific heat of
the matter of the sun. He shows that if the earth fell
directly to the sun, this would only maintain its present heat
for another 95 years J. He states that if the whole mass of
the planets were to fall into the sun from their orbits, the
* 'Dynamik des Himmels,' 1842, p. 12.
t Trans. R. S. Edinburgh, vol. xxi. p. 66.
t Thomson and Tait, ' Good Words,' October 1862.
10 NOTES ON THE NEBULAR THEORY.
heat engendered by their united collisions would only cover
the emission of heat from the sun at its present rate for
45,589 years. The meteoric theory is supported by Prof.
Lockyer * and Prof. A. Winchell f, and enlarged to the
extent of solar heat being produced by the collision of
our sun with another star by the late Dr. Croll {, an idea
originally suggested by Sir William Herschel before his
speculations upon the nebular theory .
10. The late illustrious Helmholtz, in a lecture at Konigs-
berg, Feb. 7, 1854, accepted the theory of Laplace, stipulating
a special form of gaseous matter represented by a state of
infinite diffusion in which the gas was affected by forces of
mutual and central gravitation only, but was not necessarily
in a heated state. Helmholtz determined the amount of
heat that would be generated by this form of gaseous con-
densation in the sun and planets of our system up to the
present time upon his theory. He states " that if we assume
about the 454th part of the mechanical force remains as such,
the remainder converted into heat would be sufficient to raise
a mass of water equal to the mass of sun and planets 28
million degrees Centigrade." He assumes that the greater
part of the heat was dissipated in space ages ago. He states
that the cooling of the earth alone from a temperature of
2000 to 200 degrees Centigrade would, according to the
experiments of Bischof upon basalt, require 350 million
years. To convert the same matter from a nebular state
would take a period beyond his conjecture. He supposes
the condensation of the sun to continue by his attraction
causing the falling of the surface towards the centre, and
thereby producing a continual development of heat through
pressure which, assuming the sun to be reduced by this
* < The Meteoritic Hypothesis/ 1890.
t 'World Life/ 1889.
J 'Stellar Evolution/ 1889.
Phil. Trans. 1785, p. 213.
HISTORICAL NOTES. 11
constant contraction to the density of the earth, would at the
present rate of emission take a period of about 17 million
years *, so that the sun in relation to the period of stellar life
is near its point of extinction.
11. As an important factor of the effects of conservation
of energy in the condensation of a nebula, a law of cooling of
masses of gas was discovered by Mr. J. Homer Lane, of
Washington, which is given in a paper " On the Theoretical
Temperature of the Sun " f. This law is shown in the
following manner : If a globular gaseous mass is condensed
to one-half its primitive diameter, the central attraction upon
any part of its mass will be increased four-fold, while the
surface will be reduced one-fourth. Hence the pressure per
unit of surface will be increased sixteen times. Therefore, if
the elastic gravitating forces were in equilibrium in the
primitive condition of the gaseous mass, the temperature
must be doubled in order that they may still be in equilibrium
when the diameter is reduced one-half. Under these condi-
tions the intensity of the heat of the sun must have increased
with its contraction from the nebular condition. This is a
most important consideration in showing the possibility of
the conservation of the energy of the solar system in past
time, during the continuous emission of heat from its former
more extensive surface.
12. Recently the celebrated French astronomer M. Faye
has written a learned work bringing forward much antique
lore upon the subject J. He adopts the theory of discrete
matter being originally dispersed in space, following the
theory of Kant, and of its condensation upon the thermo-
dynamic principles proposed by Mayer, by which the collisions
of gravitating matter about the sun produce its heat and mass
under certain conditions. He supposes that matter drifted
* Phil. Mag. ser. 4, vol. xi. p. 505 et seg.
t American Journal of Science, July 1870.
I < Sur I'Origine du Monde,' 2nd ed. 1880.
12 NOTES ON THE NEBULAR THEORY.
originally in cyclones, according to the whirlpool theory of
Descartes. He objects to the purely mechanical demonstra-
tions of Laplace, whom science generally regards as one of
the greatest celestial mechanics since Newton, in his theory
showing the direction of rotation the planets and satellites
must necessarily take upon exterior condensation through
contraction of a rotating gaseous system. It must, however,
be noticed in this argument that M. Faye changes the
theoretical premises from a concrete or fluid system to a
discrete or chaotic system wherein the particles of matter are
assumed to be originally moving in free orbits*, in which it
is certain that the application of the arguments of Laplace
cannot hold. It does not appear to me that there is really
very much difference between certain of the conceptions of
Descartes which are applicable to the subject, if these are
stripped of their complications, and those of Laplace. Both
these philosophers negative a chaotic state |, and recognize
the necessity for assuming an original fluid state to account
for the direction of the rotation of the planets being the same
as that of the revolution in their orbits. This gaseous state,
surrounding the solar system in which grosser particles are
assumed to float, is defined by Descartes as " ciel liquide dont
les parties sont extremement agites " J, also as " corps subtile
et tres liquid ", conceptions of a gas which do not vary
greatly from those of Clausius and Clerk-Maxwell. With
Laplace the original solar nebula moved in all parts with
equal angular velocity ; with Descartes its motion was
cyclonic, which is the only possible form of motion for a
fluid system moving with uniform angular rotation, while
condensing or contracting under gravitation, to enable it to
find accommodation for the momentum of its separate parts,
* < Sur 1'Origine du Monde,' 2nd ed. 1880, p. 264.
t ' Les Principes de la Philosophic/ p. 147.
J Id. p. 129.
Id. p. 184.
HISTORICAL NOTES. 13
as I have shown in principle in my work on the Motion of
Fluids .
13. One most important work that M. Faye has done in
this theory is to show that a discrete system of matter dis-
tributed in space, in orbital motion in each of its separate
parts, will, upon condensation under the action of gravitation
to form an exterior body or planet, cause this body to rotate
in the reverse direction to that of its solar orbital motion t
This demonstration removes a difficulty formerly experienced
in the acceptance of the theory of Laplace since the discovery
of the reverse direction of revolution of the satellites of
Uranus and Neptune. It further shows the probability that
the widely attenuated nebulous matter which may have been
present in space as a part of our solar nebula exterior to the
orbit of Saturn may have condensed at an early stage into
free particles before the concrete formation of the planets
Uranus and Neptune and their satellites. This may be
taken as a very probable hypothesis, the possibility of which
appears to have escaped the powerfully analytical mind of
Laplace.
14. In the hypothetical element of our knowledge of the
extent of time which may have been taken in solar-planetary
formation, M. Faye leaves the astronomical to consider the
geological conditions by taking the earth's superficial strati-
fication as an index of the entire past of the solar system.
This is unfortunate for one who has evidently not made
geology a serious study. In this discussion past time is
divided into Eocene, Miocene, and Pliocene periods, all of
which the geological student regards as recent J. This
error, in a geological sense, is discovered and corrected in a
second edition of his important work, but in this case it still
* ' Experimental Researches into the Properties and the Motions of
Fluids ' (Spon, 1881), p. 224 et seq.
t ' Sur I'Origine du Monde/ 2nd ed. 1885, p. 117.
| < Sur I'Origine du Monde,' 1st ed. p. 254.
14 NOTES ON THE NEBULAR THEORY.
compresses solar-planetary time into 20 million years. This
period has been proposed by eminent physicists upon arbitrary
data, but is accepted by very few practical geologists as
sufficient. Prof. John Perry has quite recently suggested
for consideration much more probable data for the time
of cooling of the earth to its present state by taking it from
a uniform temperature of 7000 Fahr., by which, upon his
calculation, the time would be extended to 100 million
years *.
Geological time, if the evidences taken from fossil remains,
the stratification of miles in thickness by slow deposition of
rocks, the removal of these rocks by erosion many times, with
erasure of faulting due to plutonic action, are fairly con-
sidered from observation and taken altogether, appears to
carry the limit of time beyond possible conception. No short
period of a few million years will satisfy the evidences of the
changes occurring in the evolution of animal life alone the
changes from one stratum to another presenting gaps evi-
dently of much longer period than the period of deposition.
If we take the earliest life we know of, the animal is still a
perfect highly organized structure, which for possible evolu-
tion indicates a long period lost to observation in fossil
remains. No one can estimate the evidences of geological
time unless he works in the field of geology. Let him follow
in the excursion of such excellent societies as that of the
Geological Association of London, stand in front of a moun-
tain of an early Silurian period, formed in part entirely
of comminuted shells of mollusks, with here and there a
perfect weathered specimen. He begins to feel the immensity
of time the generation of this life-refuse must have taken,
although he knows his observation extends over but a small
fraction of a long series of periods. The limit of infinite time
is taken by some modern philosophers in the same spirit of
* ' Nature,' Jan. 3, 1895, p. 224.
LIMITS OF THEORY TO BE DISCUSSED. 15
doubt as the limit of space was formerly taken by the
ancients.
15. No attempt will be made in these pages to discuss the
hypothesis of the diffusion of matter into space by violent
explosions from the sun and the earth and from other cosmic
bodies, as probably this hypothesis will have but a limited
time popularity. The difficulty to the serious physicist, as
shown by Lord Kelvin, is to comprehend the wonderful con-
servation of energy we find in the sun and stars for the dis-
pensation of heat and light. It is therefore physically beyond
comprehension that there could remain in cosmic bodies the
large amount of energy sufficient for the dispensation of heat
and light, and at the same time an equal or greater amount of
energy beyond that which is in any way evident, for the
diffusion of matter such as satellites, comets, and meteorites
into space by projection from their orbit foci, even if this
would really account for their present motion and condition.
Otherwise the projectile hypothesis is in every way in direct
opposition to the nebular hypothesis which it will be my
object to consider. We cannot possibly form a theory in
which we derive energy from condensation, dispense it equally
by diffusion and still have it largely conserved, as we know
it to be actually in solar and stellar systems.
16. The theory herein treated will be directed to show the
possibilities of the concentration of sufficient solar energy,
and of sufficient geological time in the past, to satisfy the
direct inferences of observation. This may be possibly best
secured by assuming our original solar nebula to be repre-
sented by such actual nebulae as we may observe with the
telescope. The nebulae selected will be assumed to go through
certain changes upon condensation, the state of which may
also be represented by other visible nebulae. In this study
we may follow closely in the theory of Laplace with deve-
lopment as far as possible by calculation of the actual motions
of some part of the solar-planetary system.
16 NOTES ON THE NEBULAR THEORY.
The proposed data, founded by inferences drawn from
astronomical observation, will entirely fall in with the possi-
bility of heat and motive energy being due to concentration
of gaseous matter in a state of infinite diffusion in revolution
in the solar system, as proposed in the contraction theory of
Helmholtz. At the same time we are bound to consider
the effects of gravity acting upon discrete matter in cosmic
formations, found in the theories of Kant and Faye, although
such matter may have been originally formed by condensa-
tion of gaseous matter. The evidence of discrete cosmic
matter rests upon the observation of the fall of meteorites
possessed of planetary velocities to the earth, which is still
taking place. Therefore, upon these premises there is the
probability that throughout the formation of our solar-plane-
tary system there were both gaseous and discrete condensa-
tions upon our sun and planets. This may be particularly
evident in periods, in an early discrete system of condensation
of the very attenuated external nebula before its planetary
condensation, and in the possibility also of discrete condensa-
tions occurring at a period when the solar nebula by radiation
of its initial heat fell below a temperature sufficient to support
the gaseous state outside the present sun. These principles
will be developed in the following pages, and the mode of
special conditions of early condensation be discussed for con-
temporary astronomical and for geological conditions in the
past. Some suggestions will be carried forward, so far as the
conditions remain active, to the present, and very hypothe-
tically only for future periods in relation to the sun and the
earth.
CHAPTER II.
CONDITIONS OF MATTER POSSIBLY ACTIVE IN THE CONDENSA-
TION OF AN EXTENSIVE SYSTEM OF COSMIC NEBULAE.
17. Time and Space. The infinities of time and space are
not definable by any mental concept. The mind can only
grasp the idea of a distant period of time and of a limited
space. If we could imagine for infinite space any perfectly
enclosed isolated space, to be filled with incandescent nebulous
or gaseous matter, such a space would continue in the same
state for infinite time, as there could be no loss of heat there-
from to condense the gas by exterior radiation to form
concrete liquid or solid matter, or to concentrate locally a part
of the energy of the system in any manner whatever. If we
please to imagine that matter originally existed in discrete
particles equally distributed in infinite space under the like
conditions, no centralized gravitation system could be formed.
Under these conditions it becomes evident, if we adopt either
the principles of the hypothesis of Laplace or that of Kant,
that we require a separate volume or an original local con-
densation to be subject to gravitational influences to form a
star or system of stars, which volume must be isolated within
the vacuous space, or in the surrounding matter or ether that
must be relatively of lower specific density.
18. Proposed Gaseous State. It has always been con-
sidered as the groundwork of any cosmology to arrive at a
clear definition of the original state of matter. If we rely
upon actual observation for our data, we have evidence of
c
18 NOTES ON THE NEBULAE THEOKY.
incandescent gaseous matter isolated in space in our observ-
able nebulae, whereas we can have no evidence of a discrete
state of matter widely distributed in scattered small units of
a few grains in weight, a mile or more apart, as some
philosophers have suggested, as such a discrete system would
be quite impossible of visual recognition. At the same time it
is the probable condition that any isolated system of attenuated
gaseous matter free to radiate heat into space will condense
at a certain stage of temperature and form solid matter, par-
ticularly if the gas is a heated form of ordinary solid matter.
Therefore, taking an original nebula to have been in a gaseous
state would not, in some cases, materially change the final
results from that of a discrete system as regards the probable
condition of condensation which may be instituted to form
the present stars, sun, or planets, if other conditions support
this theory.
19. As regards the original state of matter from which we
may conceive cosmic bodies were formed, it appears to be
most rational for the mind to assume that matter existed
originally in a pure or elementary state, and that it after-
wards became mixed or combined by the action of interior
and exterior forces acting upon it under principles which we
generally term the laws of Nature. This purity of state for
the units of attenuated matter may possibly be best conceived
by taking it to be originally gaseous, as all matter can be
shown experimentally to exist for indefinite time permanent
in this very attenuated condition where its heat is conserved
from radiation. Whereas, any system of discrete particles
or dust in the presence of gravitation acting upon it cannot
be kept in an attenuated or separate state without impression
of an exterior force, rotative or other, to act constantly upon
every particle as a means of separation. It becomes, there-
fore, convenient in this discussion, without regard to theory,
to presume some form of a gaseous state to be the original
condition, as experiment shows that all material bodies with
ORIGINAL CONDENSATION OF COSMIC NEBULA. 19
which we are acquainted may reasonably have been derived
therefrom by reduction of temperature alone, whatever state
or mass the final condensation may assume.
20. Separation of Systems of Original Matter. To support
the nebular theory of Sir William Herschel and Laplace,
which assumes that stars and solar-planetary systems were
formed from an extensive gaseous nebula widely distributed,
such as we have evidence of actually in local systems of
matter dispersed in the universe available to vision in the
telescope, and to analysis by means of the spectroscope, it is
necessary, as stated above, that we should assume a distant
period of time when a certain volume or separate volumes of
highly attenuated nebulous matter existed detached from
surrounding space yet moving within it. The volume of
such matter may be as extensive as we may please to imagine
it without changing the general conditions. It may embrace
the whole of that part of the universe we define as the Milky
Way, or for particular evidences in detail be restricted to
our own solar system. To support this theory it is only
necessary that the nebula in the system that we separately
define should have a surface boundary from which it can
radiate the heat into space which maintained it originally in
the nebulous or gaseous state. We have, by the effect of the
radiation of heat from such a system of matter, the assurance of
its constant contraction in volume, tending, by the approaching
nearness or contiguous cohesion of its parts, to the closer
accumulation of matter in a local focus or in local foci, so that
matter is thereby brought more forcibly under the centralizing
action of gravitation. The effects of the condensations upon
such foci from a gaseous system render available, upon che-
mical change of state or upon thermodynamic action, a store
of energy which is sufficient in the extent of nebulae here
considered for the formation of incandescent stars, and, if any
limited volume of nebula be taken to be locally in rotation,
for the production of a planetary system that may be finally
20 NOTES ON THE NEBULAR THEORY.
formed therefrom, after a certain amount of radiation of its
initial heat into space.
21. When we conceive that our solar nebula may have
formed a part of a general system of nebulae as defined above,
and therefore that it may have resembled other astronomical
nebulae, we may conclude that it was of that form, among the
many known forms, best adapted to produce our present
solar-planetary system upon condensation. Further, it is not
certain that the nebula of our system, taken as a motive
system, may not have gone through certain changes by which
it might at various periods be represented by various forms
of visible nebulae. Thus an originally diffused system could
not have a nucleus or central condensation until this was
formed, and when formed the nebula would possess a new
external appearance. There are known nebulae which present
irregularities of form inconsistent with condensed gravity
systems, appearing as irregular streaks and masses of incan-
descent hydrogen and helium. Such systems we cannot
assume to have arrived at their final concentrated forms,
although it is at the same time probable that they are more
complete as gravitative systems than they appear. Probably
the marked irregularity to telescopic vision in some of these
masses, particularly of the spiral nebulae, depends upon the
incandescent hydrogen and helium being the visible part of
the nebulous mass, whereas other gaseous matter, invisible
in an incandescent gaseous state, makes up the entire mass.
Such matter for instance as hydrogen united with oxygen
in the proportion to form water would be invisible under the
conditions which would render the hydrogen visible. This
residual matter, which the spectroscope does not grasp, may
possibly be detected at a future time by some new method
of analysis. Possibly it may be inferred in some cases by
refraction and by clouding effects upon more distant objects.
In nebulae that are so extensive as to suggest nearness to
us, refraction may be suggested as evidence of transparent
ORIGINAL CONDENSATION OF COSMIC NEBULA. 21
matter. In part of the nebula near 52 Cygni I$V15, the
visible nebula appears as a curved streak of incandescent
hydrogen, shown in one of Dr. Isaac Roberta's beautiful
photographs, wherein upon the hollow side of the curve stars
appear to be larger and much more numerous than on the
convex side, as though the complete nebula were of spheroidal
or lenticular form upon the concave side, invisible itself
through its transparency, yet possessing sufficient refractive
power to act as the object-glass of a telescope to magnify
and bring out stars in the background which would otherwise
be invisible in our telescopes. Dr. Roberts states that " this
gigantic nebula is of an irregular oval character ; " and that
" the bright side of this nebula seems to form a sharply-
defined boundary between the stream of the Milky Way stars
and those on its preceding side/' The photograph* for
Plate II. e e' was taken by permission from a print, and does
not do justice to Dr. Roberts's original negative. The hollow
side where magnification occurs is shown towards e'. The
dimness surrounding nebular fields being evidence of the
presence of nearly invisible matter was pointed out by Sir
Wm. Herschel. Possibly also such matter may surround
and float up the hydrogen chromosphere of the sun.
22. Tenuity of Original Matter. This is necessarily in-
sisted upon in any system of cosmology. If we take a
globular volume of gas extending to the orbit of Neptune
only as the limit of our solar system and extend the mass of
our sun and planets to this volume, we find by calculation
that the mean density of such matter would be equal to
about 1/166800000 that of air at the earth's surface. If
we extend this to the mean distance between our sun and a
near star, we should have to add many decimal places to our
denominator. Further, it is difficult to conceive that an
isolated system of matter as here proposed could remain of
* ' Selection of Photographs of Stars, Star-clusters, and Nebulae/ p. 115.
22 NOTES ON THE NEBULAR THEORY.
equal density throughout, unless the central heat was enor-
mously greater than that of the outer parts. Therefore the
gaseous matter must decrease in density in some form of
geometrical ratio from the centre to the exterior surface, and
this must produce a tenuity about the limits much greater
than that shown even by the mean density of the system
suggested above.
The speculations of Sir Win. Herschel, as well as those of
Wright, infer that the entire system of the Milky Way
formed at one period a unit system of matter. This appears
to be probable to modern science from evidences of the unity
of chemical constitution of the stars shown by the spectro-
scope. To account for sufficient tenuity in original cosmic-
matter, it was suggested by Descartes that a small mass
divided into detached particles as nearly in contact as matter
can approach may fill a volume however large. Infinite
divisibility of matter is, however, inconsistent with chemical
phenomena, which are better explained by the atomic theory.
23. In regard to the atomic theory, if we may take jointly
the calculations of Cauchy from the motion of light in solids
and liquids, of Lord Kelvin from certain electrical pheno-
mena, and of Clausius and Clerk -Maxwell from gaseous
phenomena, the mean size of the ultimate atom is about
one 500-millionth of an inch *. In the amount of diffusion
discussed in the previous paragraphs for space this would
leave less than a single atom to the cubic metre.
Therefore, if the above-stated gaseous theory is approxi-
mately correct, it is difficult to suggest that such an atomic
system formed our original nebula, even if the nebula w r ere
sufficiently heated to produce a system of general gaseous
diffusion for such atomic separation. The principles of
diffusion may be materially strengthened if we can find
it accordant with the inferences of science that matter
* Lord Kelvin, Proc. Roy. Inst. vol. x. pt. 2, p. 213.
ORIGINAL CONDENSATION OF COSMIC NEBULJE. 23
may exist in much finer division than in the atomic state
as theoretically defined above-
Sir Benjamin Brodie in a lecture on Ideal Chemistry,
delivered before the Chemical Society in 1867, suggests a
former wider division of matter than that of the atomic state
in a manner very applicable to our subject. He says : " We
may conceive that in remote time and in remote space, there
did exist formerly, or possibly do exist now, certain simpler
forms of matter than we find on the surface of the globe
a "> Xi ?? v> > an ^ s on. ... We may consider that in remote ages
the temperature of matter was much higher than it is now,
and that these other things existed then in the state of
perfect gases separate existences uncombined .... We
may then conceive that the temperature began to fall,
and these things to combine with one another and to enter
into new forms of existence, appropriate to the circumstances
in which they were placed We may further consider
that as the temperature went on falling, certain forms of
matter became more permanent and more stable, to the ex-
clusion of other forms. . . . We may conceive of this process
the lowering of the temperature going on, so that these
substances, when once formed, could never be decomposed
in fact, that the resolution of these bodies into their com-
ponent elements could never occur again. You would then
have something of our present state of things " *.
24. Suggestions for the Constitution of the Nebulce.
Pneuma. The word " nebulae " which is used in Astronomy
to define luminous cloud-like matter, particularly incan-
descent hydrogen, helium, and carbon, will, upon the
suggestion given above, scarcely embrace the entire early
attenuated form of matter that the full consideration of the
nebular theory demands, as such early nebulae must have
been formed of the constituent parts of all chemical elements,
* Quoted from William Crookes ; F.R.S., Address Chemical Section
Brit. Assoc. 1886, Reports, p. 559.
24 NOTES ON THE NEBULAR THEORY.
not only hydrogen, helium, or other gases that become visible
in an incandescent state under electrical excitation. I pro-
pose the word pneuma to specially define this most attenuated
form of gaseous matter which may have pervaded space,
composed of any or all the chemical elements, and which
represented the state of infinite diffusion proposed by Helm-
holtz. This matter would be transparent and not be visible
in any form except when undergoing chemical combination
or in condensation to form the visible nebula. The pneuma,
in condensing to form the nebula, may be assumed to
develop heat and electrical excitation, which renders the
nebula condensed therefrom incandescent at the time.
25. In the condensation of a pneuma system to a nebular
one, through radiation of heat, it must be the exterior surface
alone of the nebula where chemical action can take place,
and where heat and electricity are developed through the
condensation, which makes the nebula become in any degree
visible. A further condensation of the interior of the nebula
to form a central gravitation system or sun renders also
this centre visible by the heat due to the pressure of the
nebula upon condensation. The light from the centre passes
through the transparent part of the nebula or pneuma, which
may, or may not, at the time be undergoing chemical action.
26. Taking the subject more in detail to meet possible
conditions, the constitution of the pneuma which appears to
me the most consistent with the undulatory theory of light,
and at the same time to present evidence of sufficient tenuity
to unite the material constitution of star systems, is that of
perfect atomic dissociation of elementary matter to the extent
that every line of light or shadow, as the case may be, made
visible in the spectroscope proceeding from electrically ex-
cited highly incandescent matter represents an active factor or,
if we please so to term it, a distinct kind of dissociated atom
in comparison with which the chemical atom may be con-
sidered to represent a mass. This appears to be a most simple
ORIGINAL CONDENSATION OF COSMIC NEBULA. 25
hypothesis of the original attenuated form of matter, which
defines the factors a, %, f , v of Sir Benjamin Brodie. In this
construction we may ascribe to each kind of pneuma atom
in a free state or when excited by heat or electricity one
vibrational period only. It also accounts, from the certainty
of the great expansion in outward volume of any known
matter to produce this dissociated state, for the possibility of
the matter of any single star system extending originally
to the matter or pneuma of other stars,
27. The dissociation of atomic matter to the extent repre-
sented by spectral lines given above was originally proposed
by Prof. Lockyer as a possible state of highly heated matter
made visible by special lines in the spectra of the sun and stars,
not as representing the early condition of the nebular system
here proposed, for which this scientist holds quite an oppo-
site theory *. In his theory of the dissociation of matter in
the sun and stars, Prof. Lockyer endeavours to show that the
dissociated atoms may possibly enter into several chemical
elements represented by many lines in their spectra, so that
any element may lack the matter that produces certain
spectral lines. This is proposed to be particularly shown
in one case by the omission of certain spectral lines in the
iron group of the sun and of stellar spectra f. That the
same principles may be inferred of an original form of disso-
ciation is possibly evident in a case where there is a tendency
to a community of a certain system of material associates,
as in the yttrium group of metals, which have been found to
be possible of separation by the refined experiments on
" Fractionation " by Crookes, in which he has been able to
separate yttrium in its commercial state into five or perhaps
eight distinct elements giving special spectral lines J.
28. In suggesting a new word for the pre-nebular state of
* ' The Meteoritic Hypothesis,' 1890.
t ' Studies in Spectrum Analysis,' p, 166.
t British Association Reports, 1886, p. 583.
26 NOTES ON THE NEBULAR THEORY.
matter, it may be thought that this might be expressed by
some term already in use, as for instance the primitive fluid
of Lord Kelvin *, or by one of the numerous conceptions of
the ether as that of Prof. 0. Lodge, wherein ether is con-
ceived to be the only matter and force forming substance t,
or by protyle, the pre-nebular matter of Crookes J. Such
conceptions may possibly embrace the qualities of the original
materials of the universe, but they are so entirely hypo-
thetical that they bear no relation to experience, which takes
its first conception from structure. The indefinitely complex
and variable motivity of a fluid assumed to produce the
various kinds of known matter is more difficult of conception
than that of separate structural units. Further, if such units
can be correlated with natural phenomena as in chemistry or
spectroscopy, they become the legitimate groundwork for
the elements of a theory. With this conception the idea
herein intended to be expressed by pneuma is that it is an
active substance composed of units which represent, sepa-
rately or in combination, all the various properties of matter.
These separate distinct elements, of which there are assumed
to be a much greater number than that of our acknowledged
chemical elements, may amount possibly to 10,000 or more
factors or varieties. Upon this proposition it is more pro-
bable that chemical elements may be split up into many more
elements, than that they may hereafter be reduced in number
by finding any more generally specialized constituent material
or atom.
For conciseness in the following discussion, the pneuma-
atom, or what we may call the Lockyer-dissociation-unit, will
be termed a pneumite. The state and associations of such
pneumites will be now considered as the groundwork of the
nebular theory to be proposed.
* Enc. Brit. 9th ed. vol. iii. p. 45.
t Lecture, London Institution, Dec. 1882.
J Address, Brit. Assoc., Chemical Section, 1886.
ORIGINAL CONDENSATION OF COSMIC NEBULA. 27
29. The pneumites at the same temperature may be all of
equal size ; they must be very much smaller than the atom,
probably not over 1/10,000 of its diameter. They may
follow the conditions of Prout's or of the Newlands-Mende-
lejeff periodic law and combine consistently with producing
equivalents to di-hydrogen atoms in giving units of atomic
weight. They have precisely the same capacity for heat.
They probably possess many uniform properties which are
common to all matter besides the special individual properties
of each special pneumite, the active conditions of which will
now be suggested in relation to our subject.
30. The action of electrical excitation or of intense or pos-
sibly original heat is assumed, as suggested by Prof. Lockyer,
to have power to set any pneumite free from cohesion
to other matter where this is not subject to severe pressure,
causing repulsion between pneumite and pneumite. In this
case a pneumite may under excitation exist as a separate
free unit, if there is no surrounding pressure or local
attraction acting too forcibly upon the system of which
it forms a part to cause its combination. Upon its com-
bination with other pneumites to enter the atomic state it
will develop heat or electrical excitation comparable to that
which would cause its separation.
In the free state of the pneumite it is assumed to possess
or attain only a single rate of vibration period for each
special pneumite. The vibration period may depend partly
upon the initial elasticity of the surface of the pneumite,
which may be partly developed upon its surface as an ex-
pansion by heat, as we know no limit to the action of this
force, or as a repulsion under like sign of electricity, causing
by this expansion or repulsion from contact the separation
from other near pueumites to render it motive. This may
also produce vibrational effects from projection through
expansion causing the collision of one pneumite with others ;
the elastic motivity of which may continue in its vibrational
28 NOTES ON THE NEBULAE THEORY.
effects by reflection in collisions through the reaction of its
weight or energy in attraction of gravitation or affinity
towards its own and other matter as qualities of the special
pneumite. Any of these conditions may distinguish a
pneumite as a separate special factor of matter.
31. A physical constitution of the pneumite may be sug-
gested similar to that I originally proposed for the atom,
that of a perfectly hard centre and a perfectly tough and
infinitely elastic impressible and compressible coating * an
outward condition of matter that may possibly be inferred
f
*p'V
from the force required to bring two convex surfaces of glass
nearly together. The pneumites of equal size and at the
same temperature may possess relatively different diameters
of centres and of elastic coatings, or they may possess
diminishing density from the centre or polarity. Thus
fig. 2 a may represent diagrammatically a very light elastic
pneumite of wide or slow vibrational period, c one of rapid
period, b one of intermediate period.
32. As regards the elastic sensitiveness of any pneumite,
d may represent a very sensitive form in which the coating
diminishes in density from the centre outwards ; , a pneu-
mite with a polar axis yz, possessing vibrational influences
unequal in different directions, f may show diagrammatically
the expansion of the pneumite by heat, p being the limit of
expansion by increment of temperature up to the critical
point, p' a sudden expansion at the critical point to form a gas.
A special pneumite may be adapted to take one form of
electricity + or , so that it can only combine with another
* 'Fluids,' p. 10.
ORIGINAL CONDENSATION OF COSMIC NEBULA. 29
like pneumite under decrease of temperature through the
intervention or inclusion of a pneumite of a different sign.
33. The centre of the pneumite may be in one sense a
universal form of gravitative matter (gravite), or this may he
an element of it, upon which alone the amount of gravi-
tation and cohesion depends, while still possessing other
affinities. The resistance to combination may depend upon
the rigidity or depth of elastic coating of the pneumite, the
limiting extreme surface being, however, a constant of
perfect elasticity. In the combination of two or more
pneumites at equal temperature, #, fig. 3, may represent the
Fig. 3.
, .
gaseous state at the nearest approach of two pneumites, h
this state in combination, i two inseparable pneumites at the
same gaseous temperature. With the like factors to those
described above as the special characters of separate pneu-
mites, the final compound atom may possess any observable
qualification due to its composition. In the same manner as
the apparently similar cell in organic life possesses the
elements of the functions of the organ to which it belongs.
Taken in this manner, a free atom may be considered to
resemble in a certain degree the physical state of an organic
being, possessing potentialities which are active only when
it is endowed with the vital force of heat or electricity, suffi-
cient to produce the fluid state ; but which cease when this
influence is withdrawn or dissipated. So that the atom
remains encysted, as it were, in a dormant state, when it
forms part of a solid mass, outwardly sensitive only to the
properties of cohesion and static equilibrium, so as to be
30 NOTES ON TEE NEBULAR THEORY.
affected by temperature and electrical excitation only to a
limited degree.
If there is a distinct pneumite of entirely discordant vibra-
tional period with other pneumites, it will form a permanently
dissociated system give a single line in the spectrum have
no power of association or absorption with other matter, and
be impossible of condensation from the pneuma state. The
pneumite is assumed to be the prime mover of light vibra-
tion ; which may be communicated through ether or otherwise
to a distance.
The mode of construction proposed above for the initial
units of matter appears to me to be simpler than that
of assuming any single factor to possess at the same time
many distinct properties, vibrational, chemical, and other.
Indeed, it is easier to conceive 10,000 varieties of such
structurally simple distinct units than one endowed indi-
vidually with the many properties of the chemical atom,
needing Clerk-Maxwell's little demon to direct it.
34. In the general pneuma system here proposed as being
formed of specialized pneumites, although the pneuma may
be invisible itself when widely dispersed in space, it may
form in great bulk a density system by mutual attraction,
and even possess a certain degree of absorbent or refractive
power upon light passing through it, as before suggested for
attenuated nebulae. It would evidently in all cases be placed
exterior to the denser nebulae before its condensation thereto,
which may meet Sir Wm. Herschel's suggestion that a
nebulous appearance of stars may sometimes be caused by
their shining through an attenuated medium "*.
35. Chemical Action in relation to a Pneuma System.
Upon the data just proposed, if we assume that our solar
pneuma system originally extended to the primitive radius of
other star systems then in condensation, we may imagine
* Phil. Trans. 1811, p. 359.
ORIGINAL CONDENSATION OF COSMIC NEBULAE. 31
the synchronism of rates of vibration of certain classes of
dissociated elements or pneumites would, by equal unity or
multiple unity of vibrational period, promote association in
groups to form what we recognize as the chemical atom,
which may be compared roughly to a chord in music in relation
to its separate notes. If the atom is complex, a better com-
parison would be to the notes of an organ tuned to a certain
pitch, sometimes with omission of certain notes and with
diatonic intervals between others. The number of original
pneumites in any chemical atom may possibly be represented
by the number of lines in the intense spark spectrum, and
the strength of these lines gives the relative quantity of
special pneumites of one vibrational period in the atom. In
this form of association it follows that any pneumite group
or, as we should term it, chemical atom is that system of
pneumites which can associate with the least friction among
themselves to form more concrete matter, but which would
eject or exclude other near pneumites moving at a discordant
rate of vibration period. The excluded pneumites might again
unite in simple groups of coincident vibration to form other
distinct chemical matter. The atoms or matter formed from
a pneuma system would remain hereafter invariable and
initial to that particular system in which they were formed.
If separated temporarily by heat or electrical action they
would remain near, at positions less frictional than that cf
entering other groups, and therefore would again unite from
the same matter into the same atomic forms.
36. In the above construction it will be seen that a lower
temperature or diminished electrical excitation, by diminish-
ing repulsion or its equivalent, will permit approach and
constantly promote association, so that this association will
give a mean vibrational period to two or more groups of
pneumites of multiple accordant vibration period. Therefore
a new vibrational position in relation to the spectrum for the
first or earliest grouping. A still lower temperature may
32 NOTES ON THE NEBULAR THEORY.
produce another less divided molecular system, leaving only
a single group of molecules sufficiently active synchronously
for spectroscopic observation, the vibrations sinking by loss
of temperature or electrical excitation to a perfect molecular
concentrated condition of restricted vibration, moving below
a light-giving period of energy.
37. It will be seen also from this proposition that by
vibrational unity an element may possibly be formed minus
certain pneumites, or with a greater or less number ; as, for
instance, the spectrum of another star system, as suggested by
Prof. Lockyer, may resemble our own in certain spectral lines,
through being formed of pneumite groups or chemical atoms
from the prevailing pneuma slightly different from the solar
constituents. The sun or a star may possess a metal that
may resemble iron in many particulars and yet not be in all
chemical properties exactly like our iron, from the difference
of pneumite composition shown in the quantity of special
pneumites which constituted the pneuma from which it was
formed ; but once formed it would be universal to the special
system. Any line in a star may be omitted, or other lines
added in an approximately like chemical element. Certain
pneumites of accordant period may combine in several groups,
as, for instance, certain hydrogen pneumites of the C, F, G-
groups may be present also in nitrogen, only slightly dis-
placed from a normal position, or even in a kind of duplicate
motive action giving two lines instead of one, through
collateral or rotative vibrational influences of other combined
pneumites special to the nitrogen or the hydrogen atom.
The sensitiveness of any special group by its collateral in-
ternal vibrational freedom would produce sufficient vibrational
amplitude for spectroscopic observation, whereas another
more restricted motive group, as before stated, would fail
in this, and therefore be invisible.
38. Cohesion of Matter. Further, upon the above pre-
mises, there must be a unity of vibration-period for the
ORIGINAL CONDENSATION OF COSMIC NEBULA. 33
concrete chemical atom derived from the mean momentum of
the associated periods of the pneumites of which it was formed,
and the possibility of a like unity of atom and atom to form
the molecule. Therefore the possibility of a unity of space-
motion between like chemical atom and atom and molecule
and molecule, and thereby a possibility of near approach
when in like phase causing such atoms or molecules to inter-
lock as it were and form denser matter, or to form a local
cohesive system, to which surrounding free atoms or mole-
cules would be drawn and adhere by central affinity or
gravitational influences to form mass or visible material. In
this manner in the nebular system, as the denser masses of
associated matter, atoms, or molecules approach, through the
influence of what we may term internal cohesion to gravita-
tion-centres of attraction, the sum of these motive systems of
discordant vibrational period, or those constituted of lighter
vibrational momentum or of higher elasticity through sim-
plicity of pneumite-composition, forming altogether what we
recognize as lighter or more repulsive matter, would be
displaced to the exterior parts from gravitation- centres, as
hydrogen and helium are about the stars and visible nebular
systems. The motive energy lost by the concrete association
of pneumites to atoms, and atoms to masses may be trans-
ferred to surrounding space. This energy, being dissipated
through the outer attenuated pneuma, or the ether, will
appear as tangible heat or visible light, in its encounter with
any exterior material body *.
39. It is possible that an atomic system may be formed of
separate pneumites not of absolutely concordant vibrational
period. In this case the atoms formed of pneumites of
perfectly concordant period will be stable, and in cohesion
also stable, as gold. Atoms formed of pneumites partly of
slightly discordant period would be unstable, and the same in
cohesion. Atoms formed within the greatest possible limits
* Appendix A.
D
34 NOTES ON THE NEBULAR THEORY.
of discordant period would be explosive. Atoms in chemical
combination with other atoms of slightly discordant period
would be also explosive, although they might be per se as
regards pneumite composition of concordant period. On the
other hand, atoms may have concordant period, although
their pneumite composition may be partially discordant with
other atoms. Matter formed of such concordant atoms with
other atoms would have a tendency to associate in chemical
composition or alloy, as nickel and cobalt, the two groups of
platinum metals, yttrium and didymium, &c.
40. In a vast pneuma system supposed to be in a state of
elastic agitation through heat influences and possibly elec-
trical excitation, which may afterwards form a solar system,
we may assume that the primitive pneumites move in mul-
tiple vibrational periods, #, 3#, 25#, . . . . r, or y, 5y, 9y,
. . . . r. Since x or y may represent any number of vibra-
tions in unit of time, these pneumites would be ready to
unite into atomic systems. Therefore we may assume these
concordant atoms would form the bulk of cosmic materials.
For instance, iron with its great number of spectral lines
may be the predominant material. This is consistent with
its predominance in the meteoric matter which falls to the
earth, condensed from the universal pneuma. The last
pneumites to unite would be those at the limits of the possible
approximately vibrational period that would be capable of
forming atomic systems. These would bear some relation to
the tempered notes c J, d\) in pianoforte tuning in relation to
/, g, a. Or as ax, $x, <yx, 3a#, 5/3#, 27y# . . . r, where a, /3, y
represent the beat periods only of the vibrational time of x.
Matter formed of such atoms would be possibly rare in a
cosmic system, as the greater number of pneumites would be
selected to unite in the permanent atom-groups of simple
multiple period. Such complex atoms in /8 7 periods would
be possibly open to dissociation or to form separately material
bodies, a, 3, 11 a, . . . r, or /3, 5/3, 6/3, . . . r. Under such
ORIGINAL CONDENSATION OF COSMIC NEBUL2E. 35
refined systems of analysis as that of fractionation by Crookes,
therefore such factors of matter would represent the meta-
elements of that philosopher *.
41. Observation of Astronomical Nebula. The theory of
the nebular condition derived from observation of the bluish
or greenish unresolvable nebulae, having regard to the facts
revealed by experimental science, appears to be best explained
by assuming these nebulae to be purely gaseous. The mode
of condensation which I would suggest, which renders these
masses visible to their extreme outline, is purely chemical in
the form herein proposed and takes place within the exterior
surface of the nebula only. The nebula may or may not
possess a central incandescent nucleus. The chemical action
results in the degradation of the pneuma to a gas or a nebula,
under which action free electricity is developed.
42. In the early purely pneuma state all the elements
may combine by mixture, but still remain separate distinct
pneumites. The condensation of pneuma to the nebular state
causes matter to fall towards the centre through cohesion,
where a secondary central system of illumination through
heat may be formed by gravity, leaving an attenuated atmo-
sphere of the lighter, more permanent gases in exterior
position, as before stated. The effect of the superficial
condensation is to develop electricity, just as the condensa-
tion of water- vapour in clouds develops it in our atmosphere.
Therefore, if we could see a nebula quite near, it would
within its surface be continually sparkling or possibly be
suffused with dispersed flashes of lightning. These sparkles
or flashes would not occur in the extreme limiting surface,
which would possibly be of hydrogen and helium in a high
state of diffusion, but in a somewhat lower stratum, where
possibly air or nitrogen would form a denser layer, probably
united with aqueous vapour as in our atmosphere. These
flashes are assumed to produce the bright lines of nitrogen
* See Win. Crookes's important Address to the Chemical Society, 1888.
D2
36 NOTES ON THE NEBULAR THEORY.
or helium occasionally seen in the spectroscope. The ex-
terior hydrogen and helium, in greater tension than that of a
Geissler's tube, becomes electrically excited and forms also
an insulator to the internal matter which is under intense
chemical action, or under vivid electrization through the
chemical action ; so that we may consider an apparent nebula
as the seat of an auroral display. This superficial action of
forces, producing light-vibrations, would detract little energy
from a large volume of matter in a nebular system, whereas
the radiation of intense heat from the entire system sufficient
to produce the light we observe would detract much, and
still not account for the spectroscopic phenomena.
43. Condition of the Sun. As the sun is evidently at a
temperature above that of dissociation of the chemical
elements, it must be represented by a permanent gas, the
gravitation of the mass causing great pressure in its central
parts. Under such conditions there would still be the
tendency for the exterior dissociated pneumites to unite into
equal or multiple vibrational systems, although the elasticity
or repulsive action of the surface of the pneumite could never
at its temperature be overcome by pressure so as to allow of
a very dense system being formed. Probably the constant
tendency of the pneuma to unite into a density system in
vibrational unity is the cause of intense chemical action,
development of heat, and electricity. Through the internal
friction of the heat vibrations of the system a liquid density-
system may never be approached under present conditions.
The temperature of the sun at present, no doubt, dissociates
all elements, and projects the dissociates {pneumites} from its
surface as gas where the pressure is reduced, but such pneu-
mites cannot maintain a permanent state under the open
radiation of the sun's surface. They therefore condense to
nebulae and obstruct his direct rays, still moving at their
own vibrational period, and become light-absorbing elements.
It is probable that very refractory matter projected locally
ORIGINAL CONDENSATION OF COSMIC NEBULA. 37
outwards from the sun's surface may not reach the surface
of the photosphere, but that it condenses to nebula through
radiation at a lower depth, producing the deeper surface
of the sun-spots. These spots may, in this case, be possibly
found to be formed of a close series of absorption-lines due
to very refractory matter, which may be observable if the
central light is sufficient to pass through them to show
the inter-vibrational intervals. Therefore it is possible that
the more refractory matters invisible in the solar spectrum
of the photosphere may hereafter, with refined analysis, be
found in the spots.
44. In assuming the sun to have been condensed from an
extensive nebula which extended originally much beyond the
orbit of Neptune, it would appear at first thought that the
lighter, less refractory matter in the gaseous state would
remain at an exterior position. This has reasonably been
proposed to account for the smaller densities of the superior
planets. Upon this argument the presence of hydrogen near
the surface of the present sun appears to be anomalous.
There are, however, two reasons why it should appear about
the sun : (1) The sun derived its matter from all directions.
Tangential motion assisted in prevention of approach of
lighter matter in the planetary plane where matter was
placed most perfectly in motive equilibrium with gravitation.
Whereas above the solar poles, where all matter must
approach without tangential resistance, hydrogen would also
ultimately approach when all the more refractory matter had
condensed. (2) Within the pneuma system proposed the
pneumites of hydrogen possibly possess perfect vibrational
concord with those of a dense metal, say, palladium, and
therefore condense to vapour with it, but at the intense heat
upon the present sun-surface the hydrogen is constantly
excluded, although it remains permanently about the sun's
surface by its gravitation.
CHAPTER III.
FORMATION OF STELLAR AND SOLAR SYSTEMS.
45. Formation of Nebulce and Stellar Systems from the
original Pneuma System in tlie Milky Way. Under the con-
ditions suggested in the last Chapter we may assume that
the whole system of the Milky Way formed an immense
pneuma moving in slow rotation, the volume of which
included the original places of the matter which surrounded
and formed all the stars of the system. Such a system, of
the volume the premises infer, could not be maintained static
against gravity unless its pneuma was in a highly heated or
motive state. In the interior of the system heat would be
best conserved from radiation, therefore the exterior parts of
the system alone could radiate heat freely into space to con-
dense this pneuma into the nebular state. Taken in this
way, the parts of the entire pneuma upon which separate
nebular systems could condense by radiation into nebular
star systems would be at first only relatively near the exterior
limits of the system. The outer condensing parts of the
system would, on account of distance, be held only lightly to
the gravitation centre of inertia of the entire mass, and there
would be present certain elements of tangential action from
the rotation. The nebula would therefore experience effec-
tive resistance ill falling towards the centre from this cause
and from the motive elasticity of the interior highly heated
parts, which would become by condensation denser than the
exterior parts. Under these conditions the early formed
FORMATION OF STELLAR AND SOLAR SYSTEMS. 39
nebula must either float as it were within the surface of the
more central highly heated pneuma or be condensed into its
mass. In either of these cases the exterior surface of the
system becomes at the time of its condensation superficially a
denser system than before. Eadiation of heat into space
being constant, the surface condensation would remain con-
stant, and as the interior elasticity would be maintained by
the central heat, there must therefore be necessarily a certain
amount of tensile strain upon the exterior matter under
condensation produced by the decrease of its volume by
shrinkage from radiation. Thus there would be a tendency
for the exterior condensing matter of the pneuma system to
separate into detached parts or nebular systems formed by the
condensation of limited volumes of exterior pneuma contract-
ing upon themselves. These condensations may be conceived
to separate the outer pneuma system by tension, something
after the manner that basaltic columns in formation are sepa-
rated upon an equal gravitation plane from their uniform
matrix. After separation such unit nebular masses would
gradually draw their matter together into higher density
systems, and finally by gravitation into globular volumes, the
matter gradually further increasing in density in time towards
their own centres.
46. The condensing systems described above, if seen from
a great distance, would at an early stage resemble systems of
nebulous stars spread out upon a thinner nebular base. As
soon as the exterior parts of the nebular system formed a
more condensed or separate concentric nebular star system,
these nebulous stars would further contract upon themselves,
and then the interspaces thereby produced would permit the
free radiation of heat from the more interior parts of the
entire system of the pneuma, so that upon the same con-
ditions another concentric stratum of condensations more in-
terior than the first would again form a nebular star system,
and this again another in like manner still more interior,
40 NOTES ON THE NEBULAR THEORY.
until the whole system of pneuma here considered was con-
densing through radiation of heat to nebulae and finally into
stellar systems under initial gravitation with intense che-
mical action. Upon this principle the pneuma would be
separated into unit nebular star systems, and finally into
individual stars each radiating heat proportional to its con-
densation into universal space, as it does at the present time
in our Milky Way.
Certain local systems as here defined possessed of great
central density, if seen from remote distance, would resemble
in the whole or in partly advanced stages of condensation
some of the globular or lenticular clusters such as Messier 3,
13, 15, 53, 92, and others.
47. Suggested Motive conditions of the Original Pneuma of
the Milky Way. If this pneuma was originally motive by
rotation about a centre of inertia or otherwise, as just pro-
posed, its separate units, detached by local condensation,
would be also motive by continuity of the original momentum,
which in a perfectly fluid system would be diverted in any
direction that at the time presented the least resistance to its
motivity. There is not, however, in the Milky Way the
perfect symmetry necessary to infer an original uniform
rotative pneuma formed under simple condensation. Our
Milky Way is apparently an immense flattish bifurcating
plane of great depth formed of stars unequally distributed.
Another mode of formation may be suggested which, although
entirely hypothetical, or may be fanciful, is not altogether
inconsistent with the wonderful variations in the forms which
exist at the present time in visible nebulae. These proposed
conditions may also have partly induced the separation of
the pneuma system into unit star systems, and are quite
consistent with the motion of matter upon the nebular hypo-
thesis of Descartes, which is so ably supported by M. Faye.
48. Assuming that there were vast pneuma systems moving
originally freely in space, the tendency of such separate
FORMATION OF STELLAR AND SOLAR SYSTEMS. 41
systems in isolation under the influence of gravitation would
be to form spheroidal systems. The flattish form of our
Milky Way may possibly indicate that two such spheroidal
systems of immense volume at an early period may have
drifted together. Such a collision as would be produced at
the meeting-surface would form at once a relatively superior
density plane where the matter of the two systems would be
united, and henceforth the centre of gravity of the two
systems would be changed to the centre of meeting-plane of
the two systems. The pneuma systems being in the highest
degree elastic, would continue the momentum of their original
projection of mass in direction normal to the plane of contact
for many millions of years after impact, continuing also
to compress and flatten out the matter of the original
meeting-plane. The pressure in this plane would be increased
independently of original momentum by the action of the
mutual gravitation of the two systems in approaching to unity
throughout the meeting-surface. One effect of the compres-
sion at the meeting-surface described above would be the
development of intense heat and electrification. The elec-
trical excitation would diffuse itself through the entire mass,
possibly rendering it luminous to its extreme limits.
49. The result of such a collision after n millions of years
would be the formation of a vast lenticular pneuma more
intensely heated in its central plane, which would be more
dense from compression and gravitation than the surrounding
parts. If the two parts did not entirely combine, a bifurcating
system might be formed. The whole system would under
any condition possess a momentum compounded of the original
momenta of the two pneuma systems from which it was
formed, but in its separate parts it would possess motivities
consistent with the conditions brought about by the collision
and reflective reactions of parts of the perfectly fluid matter
of the pneuma systems. Without such a collision as herein
depicted it is possible that the condensation of the stellar
42 NOTES ON THE NEBULAR THEORY.
pneuma systems of the parts of the Milky Way would have
been much slower than they were, so as possibly not to have
advanced at the present time beyond the condition of what
may be the present state of outer matter about the galactic
poles.
50. Cyclone-inducing conditions. Assuming the pneuma to
be a most perfect fluid and elastic system of matter, upon
the meeting of two volumes of such matter, indepen-
dently of any initial rotation it might possess, must have
moved under pressure at the meeting-plane in every or any
direction which at the time offered the least resistance to the
continuity of its initial momentum. Therefore, in the meet-
ing of two fluid systems as proposed above, the direction for
continuity of motion of the outflow of these systems from the
contact plane, where the pressure would be greatest, being
supported by the momentum of the following parts, would
drive the compressed motive pneuma into directions normal
to the pressure. Under the conditions given the outflow
would be along the plane of contact and outwards in every
direction from the centre of greatest compression, thus pro-
jecting the fluid into a current plane. Such a motive plane
or current, as I have shown by many experiments in my work
on ( The Motion of Fluids ' *, engenders motive whirls in the
contiguous parts of the surrounding fluid, this form offering
the least frictional resistance to continuity of motion of a
fluid moving within a like fluid. These whirls, if formed on
the principles suggested, would in their turn engender other
friction-whirls exterior to themselves, until the entire system
became one of complete eddying motion, as it is termed.
51. As this form of fluid motion, originally investigated by
myself, is not very generally known, it may be as well to
demonstrate this hypothesis by giving an illustration which I
take from an experiment in my work on the Motion of Fluids,
* ' Fluids,' pp. 227 and 310.
FORMATION OF STELLAR AND SOLAR SYSTEMS. 43
in which the resistance to a flowing fluid in a plane of pres-
sure is applicable to the conditions suggested above. Although
the experiment referred to is on a very small scale, I have
shown that motive systems of fluid are proportional and
irrespective of scale, so that the same principles extend to
the surface motions of the North Atlantic Ocean as hold good
in the small experiment I describe * : " Take two plates of
perfectly clean glass, say about six inches square, and firmly
cement a border of card about y^ of an inch in thickness
round three sides of one of the plates with marine glue.
Then cement the second plate to the first. By this means
a very thin waterproof trough will be formed, open at the
top. If we now fill this with clean water and place it
upright in a groove in a piece of stout wood, the experimental
apparatus will be complete.
tl To observe the desired effects, the trough should be placed
before a window to transmit light through it, when the
following phenomena of original fluid projection may be
observed by the projected slightly heavier liquid diffusing
* ' Fluids/ p. 866,2.
44
NOTES ON THE NEBULAR THEORY.
itself in a current, through the constant force of pressure of
its small excess of gravity.
" Take a pen full of ink and place this gently upon the
surface of the water in the trough. The ink as it descends
slowly, by excess of gravity over the water, will he found to
divide constantly upon the resistance which opposes its direct
projection, the divided parts having insufficient momentum
of projection to move the lateral fluid tangentially to pro-
duce extensive lateral whirls. After the first division of the
descending fluid the divided parts again divide, and these
again, so that by this constant division and after subdivision
the projected fluid takes a tree-like form, the terminals
being in spiral rotation. The illustration (fig. 4) was taken
by transmitted light, exactly following the outlines of the
projection of ink in the thin trough described ; it is therefore
represented of the observed size " *. In this experiment the
sides of the trough are assumed to represent the pressure
planes.
Fig. 5.
52. The principle of lateral diffusion of whirls is seen
contiguous to any flowing stream in lateral water : the sketch
(fig. 5) was taken from the flow of water through an arch
of London Bridge.
* < Fluids/ p. 314 ; id. p. 310.
FORMATION OF STELLAR AND SOLAR SYSTEMS. 45
In this matter we might consider the separate motive
cyclonic volumes of nebulae in a very attenuated system to be
an early form of projected matter inducing rotation in stellar
formations, as in the theory propounded by Descartes and so
ably supported by M. Faye. These motions must, however,
be considered to take place strictly within the pneuma, and
would not be the cause of its condensation or separation into
stellar systems, the conditions of which as effects of radiation
have been already discussed, 45.
53. Formation of Spiral Nebula and Stellar Systems.
Taking any separate unit system of pneuma as a part of the
system just proposed or any other, we will assume this to be
in uniform angular revolution, its exterior parts moving with
a velocity below that which would project them in an orbit.
The outer matter of the system being assumed to condense
through radiation, then particle would approach particle as
the near parts of vapour in the atmosphere do to form rain-
drops. Such particles or drops would follow in the general
drift of the residual vapour of other matter that could con-
dense only at a lower temperature as rain-drops fall through
air. Under these conditions the earliest condensed outer
matter would drift as a discrete system in showers or con-
gregations or concatenations under the surrounding resistance
in spiral lines towards the centre of the system with increas-
ing velocity owing to acceleration by gravity *. Such con-
gregations of material discrete particles under the influence
of mutual local attractions would present a feathery or floc-
culent appearance on the breaking up of the outer pneuma of
the system. They would possibly be illuminated by friction
on electrical excitation. As soon as the isolated flocculi
drifted in spiral paths sunward or to the star-centre, other
surrounding condensing matter would follow in the same
direction by initial gravitative influences, and form currents
* Newton's ' Principia,' Lib. ii. prop. xv.
46 NOTES ON THE NEBULAR THEORY.
in certain positions piercing through the minor resistances of
the lighter interior gaseous matter which condenses only at a
lower temperature. In this manner a condensing nebular
system moving in spiral lines sunward would appear, if seen
from a distance, to be a perfectly stationary system, although
its condensation might be progressing at a rapid rate, as the
same position of spiral stream-lines of drifting flocculi would
be constantly conserved locally. This may be the most
general form of nebular condensation.
54. Solar -Planetary inducing conditions in Spiral Nebulce.
If the original tangential motion of a pneuma system,
condensing with acceleration of its flocculi through gravita-
tion into a spiral nebular system, attained sufficient velocity
through gravity to maintain the flocculi, drifting as above
proposed, at a certain position in an orbit exterior to the
central system of the pneuma, this matter although in revolu-
tion would remain in equilibrium at a certain distance from
the central sun or star, just as though it floated on frictionless
water. It would thus draw its separate parts together within
certain limits by its own internal initial gravitation and the
drift of following parts, so as to form a separate nebular
condensation or zone exterior to the centre, which thereby
ultimately would become in a condition to form a planet.
The direction of rotation of such an orbit-zone or planet
will be discussed hereafter. In the above we may see
clearly the possibility of a partially discrete system of
condensation of exterior matter becoming a factor of solar
nebular planetary formation.
Upon the conditions proposed in the above and the pre-
ceding paragraphs, we may suggest that, in the condensation
of the volume of pneuma necessary to form a solar-planetary
system, a nebular system may be formed at a certain period
by central condensation, which will maintain the nebular
condition about the centre, but that this may be surrounded
at an early stage by discrete condensations falling thereto,
FORMATION OF STELLAR AND SOLAR SYSTEMS. 47
formed by local exterior condensations due to excess of
ratiation of heat from the periphery of the system, so that
the purely nebular condition for the entire system may appear
in some cases in an early stage only. In this construction
we have certain factors of the nebular theory of Herschel
and Laplace in conjunction with the discrete theory of
Kant and Faye, which may be possibly observed active in
such nebulse as that of Messier 51 in Canum Venaticorum,
Plate II. /.
55. The Permanency of separate Star Systems after
formation. If we take gravitation to be a force active at all
distances of centres of masses according to a given law, its
motive energy being in inverse proportion to the squares of
distances, and if we conceive condensations to be originally
nearly equally distributed within the limits of a unit system ;
then all these aggregate or separate systems of matter,
although originally in perfect equilibrium, would drift,
though slowly, towards one another.
56. We may, however, assume other conditions to prevail
under which the permanency of separate stellar systems as
local aggregates, when once formed, might be maintained.
We may take gravitation to be inactive beyond a certain
radius as a possible condition under which stars once formed
would remain permanently fixed in space with relation to one
another. It is, however, more cogent as the law of gravita-
tion has been found to hold exactly under every test of
experimental observation within the limited though extensive
areas circumscribed by the orbits of double and multiple stars
of long period to assume that this force follows the law of
inverse squares for all distances. Under this condition a
stellar system may nevertheless be permanent if we assume
a universal revolution of stars about a common centre of
inertia, as originally proposed by Wright and afterwards by
Sir William Herschel, the principles of which are exemplified
in our own planetary system. This does not, however,
48 NOTES ON THE NEBULAR THEORY.
necessarily suggest a unit centre of revolution for all stars, or
even for those which compose the Milky Way. The cyclonic
systems just proposed would at least be inconsistent with this.
There is space enough for many centralized gravitation
systems within the more universal system of the Milky Way,
in which the stars are placed at distances from one another
far too great to render gravitation active upon the members
of any separate system beyond producing slight variations in
the forms of the stellar orbits surrounding the nearest or
strongest central attraction ; although there may be even
over and beyond this a general drift or circulation of the
entire system or any part of it in which the separate systems
here considered are embraced.
57. The influence of the knowledge of our solar-planetary
system acts so powerfully upon the mind, that it is difficult to
conceive the action of gravitation upon cosmic bodies other-
wise than with certain elements of tangential motion by
which they move symmetrically in a plane about a centre of
inertia. In the wide distribution of stars in all directions
this may not be universal. It is quite possible and consistent
with an original fluid state, that stars may not always form
part of a closed system drifting in a circular or elliptic orbit.
Such orbits may be contorted in any way by surrounding
influences and still retain the elements of original sidereal
momentum. The evidence of the variety of form taken by
gravitative matter in the distribution of stars in star clusters
and in some nebulse appears to show that stars and matter
move sometimes in a system of stream-lines, following one
another in a form we may term pearling (as pearls of dew) .
This applies to the actual appearance only, not to the mode of
formation. Sometimes these pearls or stars drift in spirals or
cyclones, in like manner to the matter that forms the system
of bivolutes in M. 51 Canum Venaticorum, M. 74 Piscium,
1$ I. 168 Ursse Majoris, as shown in Dr. Roberta's beautiful
photographs. We can but conceive that there must never-
FORMATION OF STELLAR AND SOLAR SYSTEMS. 49
theless be beyond this throughout all matter, if gravitation
be universal, a tendency to approach of mass to mass which
can only be resisted by a motion in discrete bodies in which
there are certain elements of tangential direction, and this
must ultimately tend to cause the whole of any system of
matter to approach a symmetrical form of orbital motion
about its centre of inertia, which may include the orbital or
other motions of its separate parts, as in the case of the sun
and planets ; but the time necessary for such a complete
formation in the universe would appear to be so far infinite
that it may never nearly have approached completion in any
large division of the stellar system.
58. Distances under which Gravitation may be active. It
may be difficult in some cases to imagine the disturbing
influence of gravitation at so great a distance as we know
matter to exist in stellar space, as inferred above. But, as it
is proposed that the action of gravitation is unlimited in
space, acting upon free bodies according to its law of accele-
ration, then a small attraction upon a very distant free body,
where the general composition of motions permits approach,
will produce a great velocity in a period which may be
relatively short for past time. Assume any free body, at a
very distant period, to be moving towards our sun with a
velocity of one centimetre a year, which we may take as a
quite impalpable motion in space ; still in one million years,
if the body remain in relative position towards the sun as
regards exterior influences, it will have attained a velocity of
approach of ten kilometres a year ; and this velocity would
increase with time in like ratio, until in n millions of years,
some small fraction of the past, it would fall towards the
sun with velocity equal to or greater than the highest ever
observed within our system.
59. Suggested action of Gravity in time in the formation of
Circular Orbits. If gravity is instantaneous for all distances,
an orbit once formed must remain constant in relation to its
E
50 NOTES ON THE NEBULAR THEORY.
focus for all time if it moves in a perfectly frictionless
medium. But as the orbits of certain planets and satellites
are so nearly circular, it would appear that there must be
some reason for this in a circle-inducing quality as a property
of the forces by which these bodies are directed. There is
no doubt that in the condensation of a spheroidal gaseous
system of nearly the diameter of a planetary orbit, as in the
theory of Laplace, that circular or elliptical revolution might
be brought about by the resistance of the gaseous central
matter to change, owing to uniform angular velocity in all
its parts. This will be again considered. But a second
factor of resistance might reasonably be derived from a time
element in the action of gravity in a manner also originally
proposed by Laplace. In this proposition, as time is infinite,
small constant forces active in the past may have produced
great effects by the present time.
60. It becomes, therefore, more rational, whatever we take
space to be, vacuum or ether, to assume gravity acting
through this space in time, say, with the velocity of light, or
with much greater velocity. It is not in this case probable
that any time element of attraction could be detected if the
distance remained approximately constant, as we may easily
imagine the action of gravity to be induced *, and that after
induction it remains a constant for constant distance. The
change of position in approach or recession may produce a
change in the gravitation force of induction, and this may
take time. Thus, as an instance, in the approach of a comet
to perihelion under deferred increasing factors of gravity, it
would arrive somewhat behind its time, but as the attraction
would still act in like inverse ratio after it had passed peri-
helion, it would retard and deflect the body if originally
projected in a parabolic orbit into an elliptic orbit after this
passage. If the body moved in an elliptic orbit, the action
* Appendix A.
FORMATION OF STELLAR AND SOLAR SYSTEMS. 51
due to a time factor in gravitation would decrease the
eccentricity at every perihelion passage, and increase the
time of revolution in approaching constantly to a more nearly
circular orbit. The circle being the greatest inscribed area
due to a given mean rate of tangential motion, therefore we
may imagine it the state of least internal resistance and of the
ultimate motive equilibrium for the orbit of a celestial body
in relation to a single centre.
CHAPTER IV.
STELLAR AND SOLAR CONDENSATION. FORMATION OF
ORBITS.
61. Separate Stellar and Planetary inducing Conditions in
the Nebulae, according to the amount of Rotation. Under the
conditions already discussed, assuming that any isolated
volume of pneuma may form a part of the universe, we may
take it as probable that it will form a system of matter which
will contract in volume by radiation directly under the influ-
ence of gravity until it forms a central gaseous sphere or
spheroid. This, if of sufficient size, would form a nebulous
star in an early incandescent state of condensation. We may
assume that such a system if it has no rotation, or if its
rotation is slow, resulting either from the original motion
impressed upon the nebula or from matter gravitating towards
it from all directions with nearly equal momentum, so that
from this reason the combined orbit and mass of the motive
parts by the simple action of gravitation produce a globular
system in the nebulous state, such a system would form a
single isolated star moving or stationary in space.
62. On the other hand, if the special nebular system con-
sidered is in rotation or in cyclonic motion derived from this,
matter would approach the centre with much greater facility
in every direction other than in a plane extended from its
equator, where the tangential impulse of surrounding matter
would produce the greatest resistance to the centralizing
action of gravitation. So that in this case a star might be
STELLAR AND SOLAE CONDENSATION. 53
formed of all surrounding matter except that about the plane
of its equator. This system at a certain stage of condensa-
tion would therefore appear, if viewed from a distance in a
direction nearly normal to its poles, as a planetary nebula
surrounded equatorially by more attenuated matter. Such a
nebula would be in outline of oblate spheroidal form if the
equatorial nebular matter were evenly distributed about the
equatorial plane. (Plate II. a, Great Nebula in Andromeda ;
6, Messier 32 ; c, $ I. 200 ; d, M. 81.)
63. The spheroidal form of such a nebulous condensation
might be modified to any extent by unequal distribution of
the nebula about its focus into a spiral, lenticular, or
discoidal shape, its parts being still held with equal perman-
ence by their tangential impulses. Either of the above-
described systems, if in equilibrium about its centre with its
peripheral parts moving with sufficient tangential velocity to
maintain an orbital position, would be ready to separate its
peripheral matter into ring-zones or other separate motive
systems upon further central condensation, and become
finally in a state to form a solar system such as our own with
planets of greater or smaller mass inter alia moving in orbits
about its centre, the conditions for the formation of which
will be considered presently.
64. Limits of a Solar-planetary-cometary System. We
assume that after separation of any complete pneuma or
nebular system from the universal pneuma, the initial action
of gravity within this separate system would immediately
commence to form a central condensation of greater density,
as before proposed, which would react upon surrounding
matter in proportion to its mass and inversely to the square
of its distance from any part of the surrounding widely
distributed matter.
Suppose an original system of pneuma in the remote past
taking one direction only, extending from S to S', fig. 6, and
that two equal centres of condensation, S and S', were after
54 NOTES ON THE NEBULAR THEORY.
long periods slowly formed as star systems upon principles
just discussed. The neutral position at which a particle or
mass would be originally equally solicited by the gravitation
of both systems would be at X. This would be a point of
early condensation from open radiation, and at the same time
Fig. 6.
() . oc a." c c' c" V 6' 6 (S)
one of perfect equilibrium in space. From the equal attrac-
tion of S and S' upon the condensed particle, a particle or
mass at c" would be very slightly influenced to move towards
5, a particle at c more influenced, and at c still more so.
Thus, assuming gravity universal, this would give attractions
to matter to fall towards the centre S from points of rest
intermediate between S and S' with velocities inversely
proportional to the squares of the distances of S and S
respectively active upon it.
65. Like attractions would also hold with respect to the
star system S' as regards particles at the relative distances
6, b'j b". Therefore all matter from S to X, which we may
take as the original radius of our own solar pneuma system,
would ultimately form a part of the gravitation system of S
with predominant influence over S', and all matter from S'
to X would ultimately form a part of the gravitation system
of S' with predominant influence over S. Therefore it would
be impossible that any body placed between X and S' should
be attracted towards S, or in fact that S should form the
focus of any orbit of greater aphelion distance than X in this
direction. It is further seen upon this hypothesis that
cometary or other matter could only move within its orbit at
the furthest from the position X in relation to another star S'.
If matter does not fall from the positions c, c\ c" directly
upon or towards S, there must be a tangential impulse upon
STELLAR AND SOLAR CONDENSATION. 55
such matter in relation to S which directs it into an elliptical
orbit. Under any condition, if moved it could attain no
greater velocity from gravitation in passing its perihelion
about S for projection afterwards than that due to the
velocity acquired in falling the distance to S, even in a
perfectly frictionless medium. We may therefore note that
it is not possible, if gravitation is active for all distances and
matter is condensed from a uniform pneuma or nebular state,
for any body or comet to reach our sun from space other
than that which once formed a part of our own pneuma
system.
66. Action of Gravity on distant Condensations within a
Solar System. As we may assume that the condensation of
the exterior matter of the transparent pneuma would be more
rapid from radiation of its original heat into space than that
of any more centralized denser matter or gravitation-centre
included within it, a considerable volume of outward pneuma
might condense on local foci, as before proposed ; and these
could reach the central space only very slowly from their
distance under the slight influence of central gravitation
acting upon them. So that a considerable mass might be
forming at S, the sun-centre of the gravitation system, by the
attractions of a, a', a" through the centralizing force of S
before any effective movement thereto was induced in the
distant parts c, </, c", assumed to be partly under the influ-
ence of the star S'. Nevertheless, although the near matter
a, a', a" would experience the centralizing influence of
gravity sooner than the distant parts, the interior heat of
the system may be assumed to be conserved and supported
by that released by the condensation upon the central nebula
as before proposed ; therefore it would remain a gas for a
long time, producing a pressure only about the central sun.
The entire condensation of the nebulous sun would be, never-
theless, only in proportion to the radiation of heat from the
exterior parts of the nebulous system.
56 NOTES ON THE NEBULAR THEORY.
67. With respect to our owii solar-planetary system re-
garded as a rotating condensation under the conditions stated
above, we may consider the central nebula formed by pneuma
condensation at a point when its extent was represented by
N N', fig. 7, which may be a space including the orbit of
Neptune, shown centrally transverse to its plane. Then, if
we now limit the extent of directly condensing gaseous sun-
forming matter to N N', the exterior matter represented by
C" C' C being subject to greater radiation of initial heat and
fig. 7.
C" C"
receiving less heat from the condensing sun, these bodies or
parts C, C', C" might condense upon themselves and draw
matter together as before suggested and form separate masses
(meteorites), or, if moving in nearly contiguous parts in
revolution upon a centre of inertia, form more extensive
material systems, flocculi, or comets, the probability of which
will be discussed hereafter.
If the central nebulous system of 1ST N' were conservative
of initial heat in a certain degree, as here proposed, for a
time, the free separate particle or mass C attracted to the
central nebula might in time enter the nebula N N' and be
absorbed therein. If it did so, it would become heated by
the friction caused by the resistance it would encounter suffi-
ciently for it to become again expanded to gas and afterwards
form a part of the central nebulous system, increasing its
density thereby. This would not occur, however, without
producing a further condensation about the position of entry
STELLAR AND SOLAR CONDENSATION. 57
of the mass and of motion within it, leading to irregularity
of constitution of the nebular system. If the included mass
projected into the nebula were sufficiently great, it might
become an inducing factor of centralizing planetary or
satellite aggregation or bring about a disturbance of motive
directions of the matter within the system.
68. If we take the condition of matter falling from a
position C' further from the centre than that considered
above, the gravitation upon this point being less active and
the influence of the gravitation towards S' more active, this
might not attain a movement in space sufficient to reach the
central system until the latter had contracted in volume to a
radius represented by m m, which we may take for demon-
stration as the cross section of the sun's nebula when this
extended to the orbit of Mercury. In this case, if the
eccentricity of the orbit of the matter C' caused its perihelion
distance to come within m m 1 ', the mass C' would, by friction
arising from resistance, be retained in the nebula and increase
its density, or it would move in spiral lines towards the sun-
centre with velocity in proportion to its momentum and
gravity to this focus into the resistance of the surrounding
matter. If its perihelion distance were greater than the
radius m, so as not to come under the sun's attraction suffi-
ciently to be deflected from an elliptical orbit, the body would
then move in this orbit constantly for all time and become a
permanent planet or comet or meteorite of the system.
It is seen in this that it is only matter endowed with a
considerable tangential momentum from any cause that can
form a permanent planet, comet, or meteorite of our system,
and that the greater mass of condensing matter around the
sun at an early period, particularly that which was formed
outside the mean planetary orbit plane, would, in all proba-
bility, fall directly or indirectly into the sun's nebula and
become a factor of sun-formation.
69. If we consider as an extreme case the condition of
58 NOTES ON THE NEBULAR THEORY.
another mass C" still more distant from the sun, we may
conclude that the small movement induced by gravitation,
depending upon the difference of the separate attractions of
S and S' (fig. 6), at this distance would not permit it to
reach perihelion until the time when the sun had attained its
present relatively small volume. In this case, supposing it
possessed any tangential momentum, the probability of its
falling into the immediate solar nebula would be relatively
very small. Such a body would therefore move in an
elliptical orbit and become a permanent comet or meteoroid
of our system. A condensed mass at a still greater distance
from the sun, and nearer S', would not in the past time have
reached our sun, so that it may only at a very remote period
become what we should recognize as a comet if of sufficient
outward volume.
70. In the above construction, in considering exterior
matter to be separately condensed and to reach the solar
focus in time proportional to its distance, this distant exterior
matter would be little affected by the gravitation-figure of
the central spheroidal nebulous system assumed to cause its
orbit to be drawn toward the nebular plane under conditions
originally suggested by Kant. Therefore the exterior con-
densations of a pneuma system would be projected at an
angle to this plane, with the reservation that the tangential
momentum would be less proportionally to the increase of
angle to this plane, if the original pneuma were ever in
uniform rotation, so that the orbits of comets approaching the
sun at angles considerably inclined to the mean solar-
planetary plane should be more eccentric than those at
smaller inclination to this plane, so far as the above stated
conditions hold.
71. Direction of approach to the Sun of matter from the
exterior of the original Solar-planetary Nebula. Formation oj
Orbits. Let A and B, fig. 8 3 be two stars, or suns, at the
intersection of the lines A B, d d r be the point of equilibrium
FORMATION OF ORBITS.
59
between these suns, where would rest in static equilibrium,
the gravitation of A and B being equal upon it. Place any
number of particles in line at right angles to A B from d
to d'. Then gravitation acting upon any of these points
Fig. 8.
a, b, c, a', b f , c', considered as free bodies, would cause them
to fall to 0, and beyond it if the impulse was sufficient, so
that they would oscillate about constantly in the mean
gravitative tangential plane of A and B.
72. If we make A a superior attraction over B, either from
nearness or excess of mass, then matter attracted from
would fall in direct line towards A. Any other matter in
one of the positions a, fr, c, a', 6', c', although it would
receive less attraction to B than to A, would move in angular
direction towards A in composition with the pull of B upon
it. Therefore the composition of forces A and B would
induce a definite amount of tangential motion upon all the
points a, 6, c, a', Z/, c' moving towards A. As the objects
represented by points approached A in moving in their
orbits, the influence of B would diminish in gravitation
proportion ; A becoming entirely dominant when the matter
of any of the points approached the perihelion of the orbit
whose eccentricity was induced by the tangential element B
acting upon it.
60 NOTES ON THE NEBULAR THEORY.
73. It is also seen by the above diagram that if the masses
are distributed at equal distances upon the tangent d d'
there will be many such masses a, b, c, a, b', c', influenced by
the attractions of B in falling towards A, whereas in the
direct line there w r ill be no tangential influence from B.
Therefore, the general paths of bodies falling from space
from surrounding attraction under a superior attraction, will
possess elements of tangential motion in reference to their
predominant attractions which will induce them to follow
elliptical orbits, and the case of a body falling directly from
distant space upon the sun or a star will be exceptional. The
principle here shown by diagram applied to two stars or suns
will apply equally to any number taken in separate pairs
distributed as they may be in space.
74. As regards the direction of the orbit of any free body
passing under the influence of the sun's attraction, it will be
seen that the amount of tangential motion induced by B upon
d' acting in the direction shown by the arrow e' will approxi-
mately direct the path of the body in the line p' p', in its
orbit in a left to right direction at perihelion round the sun
and back to its first position. In the same manner, a body
projected to A from d with the tangential component induced
by B in the direction of the arrow e, will follow the path p p
in a left to right direction in the plane of its orbit.
75. If we regard any initial motion of the circumscribed
system about our sun in the direction of the arrow " as an
original nebular condition, then we may assume that the
influence of B upon matter projected towards A is neutralized
at some point, say 6, so that b will fall more directly towards
the sun A than 0, and the scale of distance for projection
from this point b for the other points d, c, a, a' will be equal
to that previously defined for the point as regards tangential
action in inducing direction of revolution. In this case the
whole system of separate attractions as motive forces may be
assumed to be displaced by this initial direction of motion,
FORMATION OF ORBITS. 61
and the preponderance of direction will be that of the initial
tangential motion of the whole system, but not of every
element of it.
76. The above scheme, fig. 8, which is assumed to be that
of the form of gravitation action between our sun and every
near star, may be placed at any angle or direction to the
polar axis of the sun where the star appears. If matter in
the positions a, 6, c, d, a', b', c', d' , shown by the diagram,
were projected at an early period near the mean planetary
plane, the exterior body would fall into the planetary nebula,
combine with it, and enter into composition with its motion.
This must have been the condition of some of the early
comets, assumed to be flocculi condensed within the superior
influence of the sun's nebula ; and as these condensations
must have formed in all directions with regard to the sun,
the comets left at the present time in our system must be
much fewer or more particularly of much less mass in the
mean direction of the sun's equator and the planetary plane,
than in the direction of the solar poles. This condition is
not, however, absolute for all points, as a near star in the
direction of the solar pole or any other direction would as a
gravitation centre cause much less matter to fall directly
towards our sun than that which would fall in the direction
of a more distant star or from an intermediate space. This
subject will be taken into consideration further on.
77. In the construction shown in the diagram, fig. 8, it
must be clearly observed that unless the entire system is in
motion in relation to a gravitation centre, as shown by the
arrow 0", the sum of the deflections of the points a, 6, c,
a', b f , c' towards the plane AB would be equal ; so that no
rotation would be imparted to the sun A or a planetary
system connected therewith by the momentum of the united
masses of this matter if it was impressed upon the sun's
nebula at any period. This does not appear to be clear to
some authors who have considered the subject without
62 NOTES ON THE NEBULAR THEORY.
proposing clear definitions which, it is hoped, the diagram
may supply. Kant suggested that the sum of collisions from
exterior matter attracted from all directions towards the sun
from space would direct his revolution and that of the planets
in one direction as a resultant. Herbert Spencer adopts this
view *.
78. M. Faye shows that the mean momentum of all
surrounding bodies drawn in direct line by gravitation would
not impart any revolution whatever to a central system f. This
is herein demonstrated ; so that although all comets may
be considered as extreme condensations that take one or the
other direction of revolution in long elliptical orbits, upon the
principles discussed above, yet, if they were retained within
a nebula surrounding the sun at perihelion, unless the nebula
possessed original rotation, the mean motion produced upon
the rotation of this central nebula would be approximately
nil. Taken in another form, excluding original rotation, we
might conclude that the probability is that the mean momentum
of all the comets of our system is approximately ra7, there
being possibly as many, or, more exactly, as much exterior
matter moving from space in one direction as in the other.
79. The Formation of a Planetary Plane. Under the
above-stated condition, during the time that the sun remained
an extensive nebula any exterior body entering this nebula
at high velocity must have become dissociated and incor-
porated therewith by the heat engendered in the nebulous
matter through friction, its initial momentum being com-
pounded with that of the nebula into which it was projected,
as before stated. Therefore, all exterior projections into the
sun's nebula will be drawn towards a line passing directly
from one sun to another predominant sun as the linear
direction of greatest attraction, and upon this principle the
* Nebular Hypothesis," The Westminster Review, 1858.
t ' Sur POrigine du Monde,' 1885, p. 134.
FORMATION OF ORBITS. 63
final mean equatorial plane of revolution of the solar system
must have become that of the mean directive influences of
attraction of all the near stars or other matter that surrounded
it, at the period of its formation, in combination with the
momentum in revolution of its original pneuma or nebular
system. This does not, however, infer that the sun itself
rotates in the mean plane of the original nebula. Its plane
of rotation would be largely influenced by the amount of
matter that was condensed upon it from any direction and
the momentum imparted thereby. This will be considered
further on.
80. Planets formed at the Perihelion of Cometary Orbits.
Under the condition that the greater part of the matter that
was locally condensed, falling sunward from interstellar space
within the radius of the sun's superior attraction, would fall
into very elliptical orbits, diffused matter would become much
more dense near the sun where the perihelia of the projections
meet. Therefore, if we conceive the sun to be at any period
in a state represented by any of the spheroidal planetary
nebulae, so that the nebular density decreased constantly
from the centre of the sun, such a system might continually
contract in volume by radiation and yet maintain a similar
outward state from exterior pneuma projections thereto.
If the perihelion distance of any such condensation as
described above fell within the attenuated nebular system
about the sun, its after projection therefrom would be of less
velocity, so that it would follow an elliptic orbit of less
eccentricity. A second perihelion contact with attenuated
matter about the sun would again act in like manner, so that
by perihelion resistance matter projected thereto might finally
fall into a nearly circular orbit. If the resistance were of a
certain value the above conditions would occur at a single
perihelion contact. If the resistance at perihelion exceeded
the momentum required to maintain a nearly circular orbit,
of about perihelion distance, the projected body would, as
64 NOTES ON THE NEBULAR THEORY.
before stated, drift in spiral lines towards the centre ; or this
resistance might be partial, so that it might rest in orbital
equilibrium in a certain internal position and become a part
of the permanent nebula or planet moving henceforth in a
nearly circular orbit. If its perihelion of projection glanced
upon the outer surface of the solar nebula, entering it only
sufficiently to be deflected from the resistance, the projected
body might remain nearly in contact. This must, however,
be a special case. The near comets may have been the result
of such glancing conditions. The planet Pallas may have
been formed under similar conditions from a comet that
glanced upon the limit of the solar nebula sufficiently deep to
be resisted at its head, until its tail coming forward in the
same direction condensed about the head and formed a
nebulous planet, to be henceforth projected in an elliptic
orbit of small eccentricity. The nebulous planet would
afterwards condense to its present state by radiation and
initial gravity.
81. In the formation of our solar-planetary system, the
fact should never be lost sight of that the entire planetary
system is of relatively small mass in comparison with the
central solar system, being probably not over 1/700 part,
including all planetary, cometary, and meteoric matter.
Therefore the parts of the solar-planetary system which
attained orbital velocity during the nebular condensation at a
distance from central solar nebula, as a resultant of original
rotation, acceleration through centralization by gravity, and
by the perihelion retention of exterior matter here proposed,
must altogether be taken to form but a small part of the mass
of the entire system. In the further discussion of the forma-
tion of the planets this conception of the subject will always
be inferred.
CHAPTER V.
DISCUSSION OF THE MECHANICAL PRINCIPLES UPON WHICH
OUR SOLAR - PLANETARY SYSTEM MAY HAVE BEEN
FORMED. SUGGESTED DEMONSTRATIONS OF THE THEORY
OF LAPLACE, WITH SOME MODIFICATIONS. LIMITS OF
A COMETARY SYSTEM.
82. Energy of the Solar System. It may be held that
Lord Kelvin has shown demonstratively that the energy of
the solar system could not, even if it were produced by a
discrete condensation of cosmic matter, have been maintained
by this form of condensation throughout the narrowest
possible limit of past geological time ( 9) *. Therefore we
have no theory heretofore offered of a condensation system
by gravity to represent the formation of our solar-planetary
system with any reasonable probability other than that of
Laplace and Helmholtz. Nevertheless it is not probable that
our system was formed by any simple single mechanical
effect of the action of forces upon surrounding universal
matter, as generally assumed in special theories, but rather
that all possible conditions were active that may have con-
spired to produce the final results. Some of these conditions
will be now suggested and discussed.
83. Asymmetry of our Solar-Planetary System. If we sup-
pose our original nebula throughout its entire volume to have
been in a uniformly purely gaseous state and of symmetrical
* Trans. R. S. Edinburgh, vol. xxi. p. 66.
F
66 NOTES ON THE NEBULAR THEORY.
form, as, for instance, that of a spheroid in revolution we
should then, no doubt, if the entire system remained gaseous
until all the planets were consecutively condensed at the
exterior limit of its nebular equator, according to the theory
of Laplace, expect to find the planets in symmetrical order of
distance and of mass. In this case, with proportional time-
condensation, under the increasing amount of tangential
impulse due to centralized condensation into gravitation,
which produces the law of orbit, the distances of the planets
from the sun and their separate masses would be symme-
trically proportional, in accordance with the pull of gravitation
and the tangential momentum of the amount of the con-
densed matter.
84. That our solar system does not possess the above
described symmetry is evident from its formation. We have
between Jupiter and the earth, particularly, planets in mass
and density in no way proportional or symmetrical with
others. The planets exterior and interior to the asteroids,
taken by themselves alone, have some points of resemblance
in density and in magnitude. The exterior planets fairly
resemble one another in number of satellites, assuming that
Neptune may have several more than the one visible through
our telescopes ; so that so far as these conditions go we might
roughly divide the system of planets into two classes. We
might also possibly make a much more important division, in
a formative sense by separating them according to the
direction of rotation, by which the outer planets Uranus and
Neptune would form a class by themselves. Notwithstanding
all these minor classified resemblances, there evidently
remains beyond this a general want of symmetry in the entire
solar-planetary system. Therefore, if we conceive an original
uniform gaseous or a generally symmetrical system for our
primitive nebula placed under the condition of uniform
condensation, according to the theory of Laplace, we must
conclude that this system has experienced material modi-
DISCUSSION OF MECHANICAL PRINCIPLES. 67
fications during the period of condensation to form our
planetary system. This will be now considered by taking at
first as groundwork the effects of the condensation of a purely
symmetrical nebula, and afterwards suggesting what modifi-
cations there may have been in some parts of the system.
85. A Symmetrical Gaseous Solar- Planetary System. We
may take our solar system in its nebular state at a certain
period to be of the simplest construction shown diagrammati-
cally by fig. 9, which is intended to represent a very oblate
spheroid in revolution upon its symmetrical axis, a a . We
Fig. 9.
may assume that the whole spheroidal surface of the nebula
would be radiating heat equally per unit of area into space.
The volume of nebula in a gaseous state would therefore be
limited at any time by the quantity of matter that could be
maintained in this state, by the initial heat of the primitive
gaseous system, together with the amount of heat given out
from the centre, where there would be a sun-forming con-
densation.
86. In the above-stated case the important heat-maintaining
centre or incipient sun would react through its condensation
as a heat-radiator to the surrounding nebula, and disperse its
heat due to condensation in proportion inversely to the square
of the distance from the incipient sun-surface. The heat-
radiants being therefore equal at equal distances from this
sun, would tend to maintain a circumscribed globe of nebula
68 NOTES ON THE NEBULAR THEORY.
in a gaseous state, if its exterior temperature was falling.
We may assume that this inscribed imaginary hotter globe,
fulfilling the condition of equal radiants, would be so large
that its surface could just be inscribed in the oblate nebulous
spheroid which we now take for our complete nebula, as
shown by the inner circle of the figure.
It is readily seen that matter placed outside the theoretical
globe suggested above would be more rapidly lowering its
temperature by radiation, from its greater extent of surface
in proportion to its depth of volume, than the matter of the
inscribed globe. At the same time this external matter would
be receiving less heat from the sun-forming centre. The
peripheral matter in the general revolution of the system
would also possess its highest tangential velocity in the
equatorial plane.
The whole of these conditions, upon loss of heat of the
system by contraction through radiation, would cause a stress
at a certain nearly cylindrical plane parallel to the axis of
rotation, wherein internal or sun-forming matter would, by
continuous cohesion or gravitation, in the gaseous state, be
drawing away from the peripheral zone, which was moving
at higher tangential velocity. This zone, by continuity of
radiation of its own heat after its detachment, would be
induced to contract by condensation upon itself.
87. In this manner, if we assume peripheral matter to be
proportionally distributed about the axis of revolution of a
spheroidal nebula, the stress-plane would be that of the
separation of the peripheral .matter, which might then form a
detached zone or ring upon the theoretical conditions given
by Laplace. The extent or distance of the ring from the sun
would depend upon the extent of the globe of centre-tending
condensation maintained by the central heat at the time.
That is, really upon the contraction at the surface of such a
globe as herein imagined, by loss of its heat through
radiation.
DISCUSSION OF MECHANICAL PRINCIPLES. 69
In the separated ring or planet-zone, as here suggested,
we presume a perfectly equal distribution of matter about the
equatorial regions of the oblate spheroidal nebula ; but as we
take the conditions of radiants from the sun- centre, the same
principles would approximately hold if the ring were more or
less incomplete or denser in any part. The accident of a per-
fect ring or system of rings which occurs around Saturn may
be conceived possibly to be a unique phenomenon of the nearly
equal distribution of cosmic matter about a gravitation-centre.
88. The principles here discussed are a possible explanation
of those given by Laplace, under which the nebula forming
the exterior planets would be consecutively abandoned.
Whether there may have been some modifications of this
during the condensation of our own planetary system will be
discussed hereafter, but to follow our theme, we will take a
uniformly distributed nebular system in revolution as being
of spheroidal form, in which case the nebula might con-
tinuously go through the same set of changes as consecutive
zones or planetary systems were detached from the central
sun-system. Thus, assume (fig. 9) aba' b f to represent
diagrammatically the nebulous spheroid in section with axis
a a! and equatorial plane bb f . The sun-forming central
matter under condensation, at a certain period maintaining
equal heat-radiants, would circumscribe S. The zone of
planet-forming matter supposed to be moving at orbital
velocity, upon condensation of the sun to a certain extent
would have its annular centre of gravitation circumscribed
about p p r . The lateral exterior matter X, #, #, #, upon
condensation would fall upon the sun or the planetary zone
in gravitation-equation.
89. It will be seen that the zone-ring pp r , although de-
tached, would still for a long time maintain its condensing
condition, so that the central axis of the section of the ring
might by condensation of surrounding matter become in time
incandescent, or hotter than the nebulous sun. Therefore,
70 NOTES ON THE NEBULAR THEORY.
the sun in the interior of the equatorial orbit-plane of this
zone b b' would, through heat-exchanges, not suffer much
loss of heat, whereas at the same time it would be radiating
heat freely about its polar surface a a' constantly into space to
cause the sun's contraction in this polar direction. Further,
after separation of a ring, during general contraction of the
now separated central nebula its equatorial parts would keep
up its extension in this direction by tangential momentum,
and form a closed system by the attraction of matter towards
the axis of the ring, which, as before stated, would become
heated in proportion to the activity of its condensation.
90. Under the conditions proposed above, heat could be
freely radiated from the polar regions into space to cause the
contraction of the nebular sun in this direction ; but this
could not occur about the equatorial regions, where heat-
exchanges with the condensing zone would prevent free
radiation into space. The difference of local contraction-
areas upon the surface of the solar nebula, in conjunction
with the tangential momentum of its peripheral parts, would
cause it to return to its oblate spheroidal form but of smaller
volume. The spheroidal form would also influence gravi-
tating matter to fall towards . the plane of the solar equator,
as suggested originally by Kant and shown more definitely
by Newcomb for attraction toward an oblate spheroid *.
All these conditions show that after separation of a zone-ring
the system would again become oblate and in a condition
to separate another planet-zone therefrom about its equator
upon the same principles.
91. It will be seen that the surfaces of the sun and the
planet-zone that would conserve their heat, therefore their
nebular condition, would be those parts directly opposite
to each other. Whereas the outer periphery of the detached
zone-ring would be freely radiating its heat into open space,
* l Popular Astronomy/ p. 513.
DISCUSSION OF MECHANICAL PRINCIPLES. 71
so that the contraction of the zone-ring upon itself by con-
densation would be upon its outward and lateral parts only,
the inner parts retaining constant nebulosity by exchanges of
heat with the nebulous sun's surface, as before stated. The
contraction of the condensed outer matter would also be
directed sunward by gravity, assuming the outer parts of
the ring were moving at less than orbital velocity, which is
necessary for the concentration of the system.
Accepting the theoretical matter for the case proposed
above, if we take the centralizing globular nebular system of
the sun at the formation of the Neptune-ring or planet-
system, the diameter of the imaginary central globe at its
full limits would then exceed the diameter of the orbit of
Uranus ; at the formation of Uranus it would exceed that of
Saturn ; at the formation of Saturn it would exceed that of
Jupiter ; and so on.
92. Modes of Condensation of Interior Planets in a Sphe-
roidal Nebular System. If we take the earliest conditions,
the outer planets might very well go through the same
transitions of the nebula as suggested above. We may
observe, however, under the conditions proposed, that heat
being always best maintained in the equatorial plane by
exchanges with the newly formed planet-rings, where also
the tangential impulse would be greatest, and the greater
condensations going on constantly at right angles to this
plane, where it was open to free radiation of heat, our
assumed spheroid must constantly and rapidly flatten out its
form of section in the direction of the orbit-plane of the zone-
ring. Therefore the early planets, say Jupiter and those
exterior to it, might be condensed from a spheroidal nebula
under purely nebular conditions ; whereas the inner planets
assumed to be formed afterwards when the spheroidal solar
nebula had become much flattened, and thereby presented
much greater extent of radiation surface to depth of volume
about the equatorial zone, may have sunk in temperature, so
72 NOTES ON THE NEBULAR THEORY.
as to produce exterior local condensation within the boun-
daries of the nebula. Under these conditions the continuity
of the former nebular state would be wholly or partially
changed. So that the planetary zone-system of Jupiter and
its superior planets might somewhat resemble the condensation
of our sun, but the inner planetary system might be wholly
or partially formed from a condensation which took the
primitive form of discrete or meteoric matter. This would
partially account for differences of density, of rotation, and
some other conditions which will be more fully considered
hereafter upon discussion of certain exterior conditions.
93. Mode of Condensation of the Extreme Outer Solar
Nebula. In this we may possibly again find a modification
or want of continuity of nebular conditions in relation to the
planets Uranus and Neptune, which may be inferred from
the direction of revolution of their satellites, under conditions
already stated. In the case of these planets, from the want of
concentrative force in the original nebula through weakness
of effective gravitation due to distance, there would be a
weaker centering-tendency of the peripheral matter. There
would also be less heat radiated inversely proportional to the
distance of the central heat-focus of the condensing sun. The
tangential impulse being assumed sufficient to maintain the
orbit of a zone-ring, local condensations might in this case
occur at first to discrete matter, and the nebular system
would thereby largely disappear. We may assume a gaseous
system so extensive that the radiation capable of producing
condensation would act superficially upon matter within a
limited depth only of the nebula ; so that gravitation would
possess insufficient energy to draw this matter, if possessed
of less than orbital tangential momentum in a gaseous state
than that which would maintain it at its radial orbit, through
the resistance of the interior nebula from the boundaries of a
system so vast as that of Uranus or Neptune, under certain
conditions suggested ( 13) and others to be discussed. This
DISCUSSION OF MECHANICAL PRINCIPLES. 73
would produce a reverse direction of rotation, as will be shown
hereafter.
94. The Breaking-up of Gaseous Zone-Systems. The
perfect state of equilibrium of nebular matter necessary for
the complete formation of a planet-ring or zone (fig. $,pp'),
if such ever existed, except among satellites, could scarcely
remain for a long time, as a slight disturbing cause at any
position throughout the extensive orbit would destroy this
equilibrium in such a manner as to permit the gravitation of
its own mass to draw its parts together into the only form of
static equilibrium that could be established, that is, a globe.
Further, as before stated, in early planetary stages the intru-
sion into the solar nebula of exterior matter possessed of
sufficient eccentricity to bring it at perihelion within the
planet-ring orbit, would cause its inclusion within this ring
owing to the resistance of the nebular matter of the ring
itself to the continuity of its projection. In this manner all
comets exterior to the system, or meteorites of great eccen-
tricity, would be absorbed if brought in orbit- contact with
the planet-ring. And although we may assume that the
mass of a comet or of a shower of meteorites projected in a
cometary orbit might not materially disturb the mean orbit
of the ring-system, it might upon its intrusion possess quite
sufficient momentum to destroy the equilibrium of a perfect
ring, if such existed. This would not only be caused by
its mass, but also by the local heat engendered, and the
elastic expansion it would cause near the place of intru-
sion, together with the local drifting force due to differ-
ence of velocity and inclination of orbit between the orbits
of the planet-ring and the intruded cometic or meteoric
matter.
There is no doubt that if a planet-ring were perfectly
symmetrical the inner attraction of its parts in a gaseous
state might, under contraction through radiation from its
own condensing matter, reduce its section until it might
74 NOTES ON THE NEBULAR THEORY.
form even a liquid ring or rings ; and this or these might
again be detached into beaded strings of satellites, a condition
which possibly holds in the case of Saturn's rings. A ring
of perfect symmetrical condensation might finally part in one
place only, and form a single satellite by its matter being
drawn together by gravitation. This was possibly the case
with our own moon, as will be discussed later on ; but such
perfect equilibrium of distribution of matter surrounding a
gravitation centre could scarcely hold to the extent of a
planetary orbit about the sup, and the zonal abandonment
principle of Laplace is maintained if the zone is even imper-
fect in its circumference.
95. Influencing Condition in Periods of Planet-formation.
Critical Temperatures. Noting the irregularity of the masses
of the planets, which cannot be accounted for by proportional
condensations in time, there were no doubt present special
inducing causes active for the time only, by which we may
assume a greater or smaller nebulous zone-system was
detached at any particular period from the central solar
system. One of these causes was most probably the effect
produced at certain times by the rapid condensation of
nebulous matter to a liquid state at its critical temperature,
within parts of the solar nebula, the mass of which we assume
to be moving at less than orbital velocity at its periphery.
Such condensed matter would, in the outer parts of the
system, be immediately precipitated nearer towards the sun.
This might not, as an early condition, be wholly possible
with dissociated matter, that would only condense to a gas,
which might suffer resistance from the elasticity of the
highly heated interior. It might have occurred after the
formation of the larger planets upon the uniform cooling of
the entire system. If the temperature of the nebula was
partially reduced at any period so as to cause it to pass from
a gaseous to a vapourous state at any radius within the solar
nebula, it is certain that the denser or metallic matter so
DISCUSSION OF MECHANICAL PRINCIPLES. 75
reduced to vapour would condense suddenly at its critical
point, by a very slight further depression of temperature, to
the liquid form. The general equable state of temperature of
the nebula might permit, for instance, certain metals in the
vapourous state to occupy large volumes, and to condense
afterwards with a very slight depression of temperature at
the critical point, causing a sudden interior collapse, and
thereby the separation of a volume of peripheral matter
which would afterwards maintain an orbit position consistent
with its initial tangential impulse. These condensations
might be at any distance from the sun within the nearly
transparent nebula, according to the density and vapour
temperature of the special element that was condensed.
The amount of nebular matter, whether very voluminous or
not, separated by the tension of an internal condensation and
moving at about orbital rate at any time would after detach-
ment maintain its free orbital position.
96. The interior of the zone-ring of detached matter would
be the stress-plane of the exterior part of the critical conden-
sation. Whether the matter condensed at its critical point
remained as vapourous cloud in its precipitation towards or
about the sun afterwards would depend upon the reaction of
the heat of its condensation, radiated from the central system
or sun at the time.
97. Upon the above-stated conditions, as far as they go, it
is seen that the condensation of matter at the critical point
would produce a permanent strain within the nebula, so that,
seeing the nature of chemical elements and their very varied
critical temperatures, the separation of planet-rings from the
central solar system is not necessarily a uniform process
depending upon a continuous condensation as proposed by
Laplace. By condensation of interior matter at its critical
point of temperature, a planet-forming zone or system may,
upon this hypothesis, be separated from the sun at a certain
time ; and for a long period after this separation the sun may
76
NOTES ON THE NEBULAR THEORY.
slowly condense nebulous matter upon itself only ; until
again, under certain conditions of critical temperature of the
materials of the nebula, another planet-zone or system may
be detached. Therefore, owing to the great differences in the
critical temperatures of known matter, the zone or volume of
detached matter may be of relatively large or small mass, and
the planet formed therefrom will be consistent with this so
far as the principle in question is active.
98. It will be observed that the condensation of any
refractory metal from its vapourous state within the nebula
would affect this particular metal only, and the vapours of
other less refractory matter would remain in a nebulous state.
Therefore, in any rotary nebular condensation, the denser,
more refractory matter, moving at equal angular velocity,
with the peripheral matter moving at nearly orbital velocity,
must always drift to an inner position in spiral lines, being
accelerated by gravitation also thereto. If the condensation
remained, it would come to rest only as regards centralization
when it attained an orbital position. Under these conditions
internal planets must be formed of denser, more refractory
matter than external ones.
A particular case of critical condensation would be one in
which oxygen and hydrogen in a mixed state, below the
temperature at which they must remain in contact permanent
gases, were united into vapour. This condensation might be
caused by a discharge of electricity, from an incidental
chemical combination of prevalent elements within the
nebular system.
99. The condensation to cloud, metallic or other, at the
critical temperature of any annulus of nebula at a distance
from the sun less than the radius of the condensing peripheral
zone would obscure the exterior matter from radiation of the
more highly heated central system, as the central heat and
light would be reflected back from the condensed particles.
This would cause the more rapid condensation of the detached
DISCUSSION OF MECHANICAL PRINCIPLES. 77
zone, whose tangential momentum would prevent its conden-
sation upon the sun. This clouding effect would be repro-
duced at any following critical condensation of the matter of
the sun system, and would again tend to condense a detached
planet-zone or system ; but it is not proposed that such a
form of condensation is alone active in our planetary system.
Other conditions have been already suggested, and will be
further considered.
100. It may be noted under the conditions given above that
a period when an element was under condensation at its
critical point about the sun would be a period when his
radiation would be materially obstructed. Therefore when
an outer planet would receive much less of his heat. Such a
period, which may in some cases have lasted many thousands
of years for the complete condensation of a single element,
may in recent geological time have produced a glacial period
upon a wide extent of the earth, under certain conditions of
distribution of land areas and direction of oceanic currents,
which I have previously considered for geologically recent
glacial epochs *.
101. Modifying Conditions. In the construction given
( 76) we assumed that an entire nebular ring, extending
possibly within 10 from the sun on each side of the plane of
the earth's orbit, was condensed to form the planet. This,
however, we may presume was not the case. Very probably,
as before suggested, the planet-forming ring was never
perfect, or if perfect it is improbable that it should have
condensed entirely at once into a single planet. Possibly
condensations to meteorites form a common factor when the
nebular system sinks below a certain critical temperature.
Therefore, the earth's nebular ring might split up into a
single planet and satellite upon one side of its orbit and be
distributed in meteorites upon the other side. If these
* British Association "Reports, 1885, p. 1020.
78 NOTES ON THE NEBULAR THEORY.
meteorites were of slightly different orbit-period from the
earth they would finally unite with it at conjunction^ but if
of the same period they would maintain their vis viva and
not be detected by any calculation in the variation of the
earth's mean course or by telescopic observation. That is,
assuming such meteorites to resemble those that fall upon
the earth, which may have fallen from outer planet-rings,
and which are generally of masses not exceeding a few
hundred pounds.
102. The greatest condensation to form a planet would not
in a uniform density-ring be at an intermediate position
between an inner and outer planet, as may be inferred from
the diagram fig. 9. The gaseous state would be best main-
tained towards the interior of the ring by heat exchanged
with the nebulous sun. The condensation would, therefore,
be on the outer surface of the ring at the greatest distance
from the sun, where heat could be freely radiated into space,
as before stated ( 89). This exterior condensing matter, if
it fell towards the sun, would cause the orbit-position of the
new-forming planet to be towards the interior of the ring.
In this position the precipitation of exterior matter falling in
spiral path would give excess of velocity from gravitation to
the interior matter beyond its original angular velocity, and
might set the planet in gravitation equilibrium for a nearly
circular orbit and in rotation at this inner position, although
the original nebula had less angular velocity, as will be
shown that it may have had further on. It is not necessary,
therefore, upon the principle of exterior radiation to assume
that a planet was formed entirely of matter of a nebulous
planet-zone ; it is much more probable that the inner con-
densations were at first upon the nebulous sun's surface,
and did not separate therefrom until a dense motive system
had been already formed in one position. Neither is it
necessary to assume in all cases a single ring or a perfect
ring-system; there may have been many imperfect or partial
DISCUSSION OF MECHANICAL PRINCIPLES. 79
rings detached before these formed a single planet, these
being united afterwards by variation of time-orbits, and
crossings of perihelia through eccentricity, or be drifting in
spiral lines inwards.
The voluminous nebula of Jupiter would affect the nebular
conditions in the formation of an inner planet. This will
be best considered in relation to the formation of inferior
planets, the Asteroids, and Mars, and the possible effects of
this nebula upon the formation of the Earth. The subject
will therefore be deferred.
[ 80 ]
CHAPTER VI.
CERTAIN CONDITIONS IN THE EARLY SOLAR SYSTEM WHICH
MAY BE INFERRED FROM THE DISTANCES AND MASSES OF
THE PLANETS UPON THE NEBULAR THEORY.
103. The Distances of the Planets from the Sun appear to
be in somewhat symmetrical order in individual distribution
of position, although their masses do not indicate any law
for their formation consistent with the condensation of a
gaseous system or of a uniformly distributed discrete system
by a decrease of density outward from the gravitation centre
or sun. The approximately symmetrical order of distances,
without relation to the amount of distribution of matter, was
pointed out by Titius in 1772 *, which became known as
Bode's Law owing to the special attention called to it by that
astronomer f. It is illustrated in the following table, the
scale of measurement being the sun to earth unit.
Table of Bode's Law.
Mer.
Venus.
Earth.
Mars.
Aster.
J up. Sat.
Uran.
Neptune.
+
4
4
4
4
4
4
4
4
4
B. eq. .
o
3
6
1-2
2-4
4-8
9-6
19-2
38-4
Theory.
4
'7
1
1-6
2-8
5-2
10
19-6
38-8
Obs. ...
39
72 1
1-5
?
5-2
9-5
19-2
30-1
* See Miss Clerke's ; History of Astronomy in the 19th Century/ p. 87.
t W. T. Lynn, ' Observatory,' vol. xvi. (April, 1893) p. 178.
DISTANCES AND MASSES OF THE PLANETS. 81
In the first line 4- '4 is given as an arbitrary plus constant.
It may be noticed that it is correct to observation, according
to the law, for the places of the Earth and Jupiter, irregular
with the inferior planets and Mars, and should be omitted
altogether as a plus constant for the outer planets, failing
entirely for Neptune. The second line in the table is in
geometrical series from Venus, which is quite arbitrarily
taken as 3. The third line gives the theoretical deduction
of Bode's Law. The fourth line gives approximately the true
distance as found by observation.
With Uranus and Neptune, there appears to be a certain
element of orbital time relations ; the year of Neptune being
about double that of Uranus.
104. The Masses of the Planets. No law has been dis-
covered for comparison of the masses of the planets, except
that the four inner planets are smaller and have a mean
density more than five times greater than that of the four
outer ones, which may indicate that their formation has been
upon a different plan. In the outer planets there is a kind
of proportion of masses to spaces, which agrees approximately
with an assumed decrement of density of nebulous matter
employed in their formation not inconsistent with the manner
in which mixed gaseous matter would probably condense
when placed around a gravitation centre.
105. Following the demonstrations of the theory of Laplace,
the density of matter to form the planet may be estimated by
reversing the process of its condensation ; that is, by the
dissipation of the mass of the planet into the assumed original
nebular zone-ring volume it formerly occupied. Assuming
that the planet will be formed upon the inner surface of the
ring, as stated above, since radiation, and therefore contraction,
must be exterior to this, we may for calculation take the mean
distances from the sun of any pair of planets and make half
their difference the radius of the ring assumed for argument
of circular section. Calling this r, the section of the ring
G
82 NOTES ON THE NEBULAR THEORY.
will be Trr 2 ; making TI the mean radius of the orbit of the ring
and therefore its circumference 2 < 7rr 1 , we have for the volume
of the ring 27r 2 r JJ r 1 . We may conceive the ring of a certain
oblateness ; say this diminishes the area of the section by
two thirds, our formula then becomes f TrV 2 ^ for the corrected
ring volume. Now taking the planet as a sphere f7rr 2 3 ,
y 2 being its radius, and dividing this into the volume of the
ring, we obtain its assumed original density in the planet's
specific density units. For comparison it is convenient to
make the unit of density that of air at the earth's surface.
Then the specific density of the earth is found by multiplying
its volume by 5' 6 its specific density compared with water
and 800 the ratio of air to water. Calling this m, the com-
plete formula becomes
Other planets may be taken in a similar manner, changing
m to m according to the data for the density of the planet.
The following table is taken from the above formula, adopting
Bode's law for the mean place of the Asteroids :
Table of Proportions of Densities of tlie Nebular Planet
Ring-spaces to the Density of Air.
Mercury .... 1/1,060,000,000
Venus 1/81,230,000
Earth 1/372,400,400
Mars 1/418,800,000,000
Jupiter .... 1/505,900,000
Saturn 1/15,960,000,000
Uranus 1/248,400,000,000
Neptune . . (?) 1/5,000,000,000,000
106. The irregularity of these figures appears to indicate
the improbability of the part of our nebula which formed the
planets having been condensed from matter symmetrically
distributed in an oblate spheroidal form, although perhaps
this may not be altogether inconsistent as a form of condensa-
tion of the four outer planets and their satellites, as the table
shows great increase of tenuity outwardly.
DISTANCES AND MASSES OF THE PLANETS. 83
107. The decrease of the former nebular density-space
between Jupiter and Saturn and Saturn and Uranus varies
about as the powers of 1*17 to 1'12, and possibly if we knew
its extent of original nebula, Neptune might follow a similar
ratio. The figures appear to show upon the ring-nebula
hypothesis that Uranus was condensed from matter weighing
only about 4*6 grains to the square mile, a degree of tenuity
difficult to imagine in a concrete system. This extreme
tenuity might, however, be greatly reduced, if, instead of
taking the oblate spheroid form before proposed we were to
assume a more lenticular shape for our planet-forming nebula,
thinning-out to a nearly flat plane, which would be quite
consistent with observed forms of nebulae seen in the heavens,
of which we are supposed to observe the thinnest section *.
Under this condition, the nebula might not vary much in
density in the outer series of planets from Jupiter to Neptune
inclusive.
108. Taking the oblate spheroidal form of nebula assumed
for our solar nebula immediately before its condensation to
planets, we may also suppose that effects of condensation
through surface radiation produced some differences. The
extensive and attenuated plane of Neptune and Uranus being
open to this surface radiation would cause the nebula about
the positions of these outer planets partially to condense into
solid matter before the large masses of Saturn and Jupiter
had considerably changed. Matter so formed and so widely
distributed as it probably was originally before the formation
of these outer planets, would scarcely condense entirely into a
cohesive gaseous system, but we might more probably have
at an early stage the formation of a motive discrete system
composed of minute minor local condensation or of dust in
the orbit-plane, according to the system of Kant and Faye.
Such a system could only unite to form a planet if the original
* IjF I. 200 Leonis Minoris, Plate II. c ; $ I. 53 Pegasi, &c.
G2
84 NOTES ON THE NEBULAR THEORY.
angular velocity of the particles were less than the tangential
velocity of a particle in gravitation equilibrium according to
the law of orbit, so that the particles separately condensed
would fall in the direction of the nebulous sun of the period
into elliptical 'orbits. Such particles would be of different
orbit periods from differences of distance at the points of con-
densation, so that they might afterwards come into collision
at the crossing of orbits about the coincident orbit position to
cohere and form a planet ; or they might unite in the exterior
of the central nebulous system at the perihelia of their pro-
jection, which would henceforth become their orbit. This
will be further discussed.
109. Probable Form of the Original Planetary Nebula.
If we take the original nebula to have been of about the
same density at periods when the separate planets were
abandoned, we may then plot a section that would represent
the form which the planet-forming nebula would assume after
a certain amount of condensation. This would show a con-
siderable rounded projection over the positions of the planets
Jupiter and Saturn, and as the Sun would also be contracting,
this part of the nebula of the solar system would for a period
assume a convoluted discoid form, possibly as represented in
fig. 10 ; the positions of Saturn and Jupiter being shown at
S, J. In the present construction we are considering the
planetary forming nebula only which will be about the orbit-
plane, and omitting all consideration of the circumscribing
sun-forming pneuma system, which would maintain the
spheroidal form.
110. In accepting this form, it is extremely probable that
there was some external cause for the exceptionally large
masses of matter in Jupiter and Saturn. Possibly these
planets represent factors of an early intrusion of a local con-
densation of the nebula that formed at a distance from the
solar plane, which was afterwards projected into it by attrac-
tion to the sun. Such projections might be constrained to
FORM OF ORIGINAL NEBULA. 85
follow a circular orbit by the resistance they would encounter
if they entered the sun's nebula at about the perihelia of their
projections thereto. As before suggested, representation of a
part of such a form of nebula seen in plan upon a large scale
may possibly be found in the great nebula of Andromeda,
Plate II., #, or in a more pronounced form in the ring-nebula
of Lyra, Plate II., g. In fig. 10 matter is shown distributed
Fig. 10.
symmetrically about the orbit-plane ; but it is more probable,
as will be seen later on, that the planet-forming disc was not
of this symmetrical form, but irregularly convoluted while
still in a nebulous state.
111. Effects of the voluminous Ring of Jupiter here proposed
upon the intra-Jupiter Solar System. In assuming an ex-
tensive zone-ring of nebulous matter for the formation of
Jupiter, the conditions that will be presented for interior
planetary formation become materially modified from the
uniformity of direction-gravitation due to the sun only, as
before proposed. In the case before us, the intervening-
interior nebulous matter towards the Jupiter-ring would be
solicited by two unequal gravitation systems, that of the sun
and that of Jupiter ; the Jupiter ring being practically active
near its surface only. Assuming the intervening matter
between this ring and the sun at the time to be wholly
nebulous, this nebular condition being assumed to be largely
maintained by the heat of the interior of the ring, there
would then be a strong tendency through cohesion for the
nebulous matter near this ring to be drawn either towards
the sun or towards Jupiter in condensation. This would
86 NOTES ON THE NEBULAR THEORY.
occur particularly from the condensation due to radiation
being greatest in relation to the depth of volume in the most
attenuated part of the nebula, fig. 10, A. Therefore in this
case the condensation would be from the surface in the orbit-
plane of the nebula and would tend to break it up into separate
superficial small local condensations. Further, from the great
extension assumed for the nebular system of Jupiter exterior
to the plane of orbit and the large volume of the nebulous
sun at the time, there would be little excess of attraction
towards the plane of orbit for nebulous matter within the
orbit of Jupiter. Therefore, upon condensation of such a
nebula, owing to the equilibrium of its position between the
attractions of the Sun and of Jupiter, there would be a local
tendency to form very small condensations or planets, par-
ticularly near the interior of the extensive nebular ring of
Jupiter. These are probably invisible from our distance.
Such small planets, at least the earlier ones formed upon the
exterior radiating surface, would possess great inclination to
the plane of the orbit of Jupiter in moving as free bodies
under the stronger influence of the sun's attraction. In the
equilibrium of position of condensation we have possibly -the
principal reason that the Asteroids are of small mass, and
particularly that these small bodies should often be found
moving in eccentric and inclined orbits, omitting extreme
cases of inclinations probably due in part to other causes
previously considered ( 80).
112. Relative Rate of Cooling of the Intra-Jupiter Sun-
system. After the sun's spheroidal volume had retired from
the inner surface of the ring of Jupiter's nebula, and this
nebula was becoming of insufficient temperature to maintain
an inner nebulous system, and many Asteroids of inclined
plane of orbit had been condensed, the remaining nebula may
have been disposed approximately as represented in fig. 10,
where the letters S, J, A, M, E represent diagrammatically
the positions of Saturn, Jupiter, the Asteroids, Mars, and the
RELATIVE RATE OF COOLING. 87
Earth. Taking this outline of the section of the nebula and
assuming surface radiation to be equal from all superficies,
it will be seen that the narrow neck M A of the nebula of
Mars and the Asteroids would by its shallow depth be the
earlier part to cool down to condensation point, leaving Jupiter
and Saturn still in a heated nebular condition. This condition
of radiation remaining constant, the Asteroids, Mars, and our
Earth would certainly be condensed to a liquid state long
before the large mass of Jupiter could have lost its nebular
condition. It therefore becomes probable that the condensation
of Mars and of our Earth may have taken place much earlier
or certainly not later than that of Saturn, so that our planet
in a liquid or solid state would be much older than Jupiter.
It is even probable that Jupiter may be considered only as an
advanced minor solar system, and that at the present time it
may not have its surface about its equator condensed to a
solid coating : this will be discussed further on.
113. After the cooling of Mars and the Earth to a liquid
or solid mass, the consecutive condensations of the inferior
system of Venus and afterwards Mercury would again possibly
more nearly fall into a system of periodic condensations similar
to the earlier condensations of the outer planets, following
the plan of consecutive exterior condensations as proposed by
Laplace, except that with the inner planets we may have had
a denser medium, or more probably a medium pervaded by
discrete matter from which these planets were condensed,
which would account for their superior densities and rotation
periods subjects that will be fully considered further on.
CHAPTER VII.
SUGGESTIONS FOR CAUSES OF DIRECTION OF ROTATION OF THE
SUN AND PLANETS. THE DIRECTION OF REVOLUTION.
VELOCITY OF ROTATION OF THE PLANETS AND OF THEIR
SATELLITES.
114. The Direction of the Solar Axis of Rotation. Let
s f s ff (fig. 11) represent the nearest stars to our sun c, and the
line of direction s r c s ff therefore the mean gravitation plane
of the planets' orbits as before defined ( 79). Let s, s, s, s
be other stars more distant from the sun than s' s /f . Bisect
Fig. 11.
i/""
*
the distances between the sun and each of the stars, supposed
of equal mass with the sun, by the arcs shown. The dotted
lines embracing these bisections would represent the extent
of the sun's original pneuma system, or that of the mean
gravitation influences between the sun and these stars.
DIRECTION OF ROTATION. 89
Assume the solar pneuma in revolution, when free from
surrounding matter through condensation, with its axis at
right angles to the plane s' s". Then it is clear that a larger
amount of matter in further condensation would fall to
the sun in the directions a a! than in the directions b b f ;
and as this matter would in condensation carry with it the
original tangential momentum of the uniform angular velocity
of the pneuma system, the equatorial plane would thereby be
elevated from the original solar plane s' s" towards a a',
the direction from which the greatest amount of gravitating
matter would fall ; so that the orbit-plane of planet- forming
matter would be s' s", but the momentum of the sun's con-
densation greatest in the plane a a' and its equator be subject
to the combined directive influences of s s" and a a 1 . The
plane of the stars taken above for illustration must be under-
stood to be purely diagrammatical ; no such plane exists,
neither could the axis of original pneuma rotation be defined,
the plane produced would be undulatory, but the principle
will hold for stars in any direction from the sun and any
plane of rotation. Nebulae that approach the spheroidal form
of which the great nebula in Andromeda may be taken as a
type (Plate II., a) are generally asymmetrical, being more
dense in certain directions *. Such systems in condensation
would not therefore produce axes symmetrical in the plane ot
orbit.
115. Direction of the Planets' Axes. If the suggested
discoid form of the planet-forming nebula (fig. 10) existed
with matter symmetrically distributed about the equatorial
plane, the planetary axis would be vertical to the plane, but it
is not at all necessary to assume the planet-forming matter
to be placed symmetrically. If it were not so placed, the
direction of rotation of a planet would be in equation with
the mean momentum of matter falling to the planetary
* y I. 200, tf I. 205, tf I. 53, M 81.
90 NOTES ON THE NEBULAR THEORY.
centre from any direction. Further, the pneuma system is
assumed to extend in all directions and that condensations
occur at its outer surface ; therefore condensations would fall
into the planetary plane in all directions, such matter being
projected in cometary orbits. Matter thus projected towards
the sun and towards the denser equatorial nebular plane
would be absorbed in the nebular system and give local
directive influences by causing intermotion within the nebula,
without necessarily displacing greatly the positions of the
planetary condensations then forming. This assumes the
planet to be of much greater mass than the units of intruded
matter falling constantly from various directions, and there-
fore such intrusions to be of insufficient momentum individually
to materially disturb its orbital position. The projection
of eccentric cometary matter would be very much more
frequent in early times than at present, as all such projections
would become absorbed in the solar-planetary nebular system.
Fig. 12.
We must assume, from the extent of a pneuma-solar
system, that cometary matter from exterior condensation
would materially affect the intermotion of the parts of any
system of nebula that was in a state suitable for planetary
condensation, wherein every planet would form a gravitation
centre with directive influences. Such intrusions only by
directive impression according to the momentum of matter
projected from any direction might disturb the mean plane of
orbit of the planet, or induce obliquity of axis by diverting
the mean revolution direction in the condensing nebula of
which the planet was being formed. Under these conditions
the theoretical general half section of the planet-forming
ROTATION OF THE SUN. 91
nebula given in fig. 10 might be changed at the point of the
commencement of planetary condensation to a section more
nearly as represented by fig. 12 for the portions of the nebula
about Jupiter and Saturn employed in their formation.
116. Rotation of the Sun. As long as a spheroidal solar
system of pneuma could remain in a state of gaseous
cohesion entirely by the effects of its own elasticity through
expansion by internal heat, so as to divert the direct
action of free gravitation of its outer parts into a pressure
upon the inner parts, such a system revolving upon its
symmetrical axis in a frictionless medium or a vacuum
would revolve entire. It would also revolve at equal angular
velocity in all its parts as the least frictional form of motion
for a 'continuous pneuma or highly gaseous system. In this
case the peripheral velocity of the entire pneuma or its more
condensed nebula must be such as will permit the exterior
part of the nebulous matter to remain in contact or in
cohesion upon the extreme outer surface of the entire system.
This entails that the velocity of rotation of any part of the
system must not exceed that which produces gravitation
equilibrium according to the law of orbit. If the peripheral
matter exceeded this orbital velocity at any time, it would be
thrown off and depart from the central system. If the
pneuma moved with a smaller velocity, it would press the
gaseous matter towards the centre, forming a nebular system,
and attain thereby a higher velocity by gravitation until
the peripheral matter, maintaining its original angular velocity
with the excess due to gravitation in falling towards the
centre, had attained an orbital velocity, and then its pressure
would cease.
117. Assuming such a nebular system as above defined,
free from surrounding exterior attraction, moving at such a
velocity that its peripheral parts could not rest in gravitation
equilibrium as free particles, but must exert a pressure upon
the system, then from any loss of heat or of internal elastic
92 NOTES ON THE NEBULAR THEORY.
force the tendency of all exterior matter would be active to
press forward towards the centre, as the virtual velocity
would be less in any interior part than that which would
separately maintain its matter at the original distance of
radius in a free state of orbital motion. Upon this con-
dition the surrounding pressure within a gravitation system,
if it exceeded the elastic force of the internal heat of
the system for materials in a highly gaseous state, would
form a dense mass or sun in the central part. In forming
this central dense condensation, omitting the friction of the
system which would produce heat, or assuming this equal
to the acceleration of its gravity in falling sunward, we may
take it that all matter condensed upon the sun would carry
with it the linear velocity of its former position, which would
be greater in the proportion of its original linear circum-
ference to the circumference of the sun upon which it was
afterwards condensed. This condensed matter would there-
fore rotate the sun in proportion to the mean excess of linear
velocity or momentum of the matter condensed upon it from
which it was formed.
118. To demonstrate the above proposition, we may assume
that all nebulous matter formerly condensed upon the sun in
consecutive shell-layers over its surface, at first from directive
pressure of the interior parts of the nebula surrounding it,
which we assume was moving in mass at equal angular
velocity with the centre or sun. Then the condensations
from the interior parts would impress small excess of linear
velocity upon the sun in the early or central shells of con-
densation, and the more exterior parts consecutively higher
velocity from the condensation of these more distant parts
of the nebula in the outer shells, which theoretically would
be consecutively brought down to the surface of the sun.
So that with increasing volume the condensed central sun
would attain constantly increasing velocity of rotation.
By condensation in the above paragraph, is intended purely
BOTATION OF THE SUN. 93
gaseous condensation, the condensation being due to loss of
heat by radiation from the system by which the whole mass
maintained the elastic force with which it formerly resisted a
central gravitation tendency.
119. We will assume as an hypothesis that our original
solar nebula possessed the rotation period of Neptune of about
165 years. Then, assuming this nebula of spheroidal form
every section of which was condensing by gravitation through
loss of heat towards the sun, with directive momentum in
proportion to the original virtual tangential velocity of its
parts, the mass of the nebula being for the present problem
taken to be in density inversely as the squares of the distance
of its^ parts, then, if the nebula could be entirely condensed
upon the sun to its present state without loss by friction more
than the excess of momentum due to gravitation in falling
sunwards, the sun should after such entire condensation
possess a peripheral velocity equal to the peripheral velocity
of the original nebula. That is, in the case we assume, the
velocity of the planet Neptune in its orbit. This may be
calculated.
120. The orbit of Neptune has a circumference of about
17,253,000,000 miles and his revolution period is about
60,000 days, equal to an absolute diurnal velocity of about
287,000 miles in our sidereal day. The sun has a periphery
of about 2,679,400 miles. Therefore, if the whole nebula
condensed upon the sun without friction in shell-layers within
the orbit of Neptune, the sun's linear velocity would be at
its equator equal to the velocity of Neptune in its orbit,
which would make its period of rotation somewhat under
9^ days. Observation shows the sun to rotate in about 25
days, so that the present diurnal velocity of the equatorial
surface of the sun is 107,180 miles, that is only a little over
2*6 of that which would be due to condensation of the
enclosed nebula within the orbit of Neptune, upon the con-
ditions proposed above, taken as a trial hypothesis.
94 NOTES ON THE NEBULAR THEORY.
121. Upon the nebular theory the formation of any planet,
say Neptune, could not have occurred until a large volume of
exterior matter had condensed to this position. Indeed, the
whole condensation must have taken place at the exterior or
radiation surface of the nebula at a distance within which
alone the planet could be formed, as exchanges of heat would
prevent it condensing sunward, as before stated. Therefore
the rarer portions of the nebula must have extended at an
early period to a great distance beyond the orbit of Neptune,
and the same extent of nebula must have been instrumental
in sun-formation, although the condensation to form the sun
might occur centrally from loss of general elasticity. If we
assume the original radius of the nebula to be represented by
= , where Y is the orbital velocity of Neptune and v
that of the periphery of the sun, and D the distance of
Neptune, we have for the distance d of an exterior planet
in the present case for particles in gravitation-equilibrium
according to the law of orbit about 38,000 millions of miles,
that is if the nebulous matter was moving with equal angular
velocity to that of the sun's present equatorial surface.
122. This being the radius of equilibrium of a particle
moving in a circular orbit at the distance given, would
indicate upon the principles of gaseous condensation the
fullest possible extent of our original nebula that could have
been active in motive factors upon the sun, if its density
diminished inversely as the square of its distance and the
condensation was frictionless. In this theoretical calculation,
therefore, we may take it that the angular motion of the
nebula produced the angular motion of the sun, thus leaving
direct gravitation in condensation to represent his heat.
123. In the above eonstniction, although the motion of a
planet may be used as the index of the extent of the original
nebula at an early period, yet the planet's own formation may
be excluded from the consideration of sun-formation, seeing
MOMENTUM OF A PLANET. 95
that the entire mass of the planetary matter may not exceed
T ^ part of the mass of the sun and that the result of its
formation may be entirely different, the nebulous pressure
on the sun by gravitation through loss of heat by radiation
producing an intensely heated centre by concentration of
exterior energy, as shown by Helmholtz ( 10), whereas the
energy of the planet system is expressed more particularly in
motive factors. So that gravitation under certain conditions
may increase the orbital velocity of a planet, whereas it may
be active in heat factors on the sun.
124. The Momentum of a Planet. If we assume a zone-
ring of nebula formed of uniformly distributed matter or
otherwise to be detached from the sun's nebula, and to be
moving at the orbital velocity which would be necessary for
its detachment, and that all parts of the zone-ring are moving
inter se at equal angular velocity according to the theory of
Laplace ; then the entire momentum of the outer parts of the
nebular zone, in falling towards the inner parts by conden-
sation to form the planet, will carry with them the plus
momentum of the outer parts which must appear in motive
factors upon the planet when formed from condensation of
such a system. If the angular velocity of the zone-ring
at its outer parts were correlative with the orbital velocity of
the inner parts, the gaseous system of the nebula would
extend and not condense. It therefore becomes apparent,
that to maintain the momentum of the original angular
velocity of a nebular zone, the zone must remain in some
way attached to the solar nebula during a large part of its
condensation, and this momentum must be conserved by
the intermotion of its parts.
To consider the value of the motive factors of the parts of
a condensing zone, we may take it from the period when its
outer angular velocity equalled the orbital velocity of the
next outer planet, that is at the period when its system was
detached from the solar nebula. Upon this construction we
96 NOTES ON THE NEBULAE THEORY.
may divide the entire momentum of a nebular planet-zone
moving under the sun's attraction into two factors of motion
angular motion and gravity. These we can distribute into
two constants as the final condition of condensation :
1. Permanent acceleration of rotation of a condensation
within the zone, that is the future planet. 2. Acceleration of
revolution to give the planet orbital motion. We may take it
as an hypothesis that the sunward acceleration by gravity
into the original momentum of the condensations of matter
falling from the outer part of the system gives sufficient
acceleration of revolution to establish the orbital motion :
and that the difference between the angular velocities of the
outer and inner parts of the zone-ring gives the rotational
velocity to the planet as the probable action of the motive
factors evident in the system proposed.
125. The Orbital Velocity of a Planet derived from tJie
centralizing gravity of the outer parts of a nebular zone falling
upon the inner parts. Assume a planet newly forming by
detachment of a zone at the periphery of the solar nebula, and
that this zone is condensing most rapidly at the greatest
distance from the sun. At this instant the periphery of the
solar nebula must be moving at slightly less velocity than
the detached zone, as before stated ; so that we make the
velocity of the outer periphery of the nebula of the next
inner planet zone-ring that of the orbital velocity of the next
outer planet. We have no data for this in the case of
Neptune, which must be referred to the extent of the sun's
nebula at its peripheral velocity, but we may take any other
two nearer planets whose mass is sufficient to allow of their
being regarded as nebular formations, say Saturn and Jupiter.
In these the linear velocity of the sun's nebula at its equator
could not have been so high as the velocity of Saturn at the
time the Saturn zone-ring was just detached from the sun's
nebula. If we consider these orbital velocities, we find
Saturn equals 510,452 miles diurnal velocity, that of the next
ORBITAL VELOCITY AND ROTATION OF PLANETS. 97
inner planet Jupiter 689,855 miles ; therefore, to define the
velocity of Jupiter in its orbit upon the data suggested we
require plus 177,403 miles. The plus velocity is herein
assumed to be derived from gravity of the matter falling
towards the sun, that is entirely condensing towards the
position of Jupiter.
126. The simplest possible construction to show this is to
assume that matter condensing from the outward part of the
zone was moving just below the velocity of an inner part.
Then this matter would not have sufficient momentum to
maintain its tangential position, so that it must fall into
an elliptical orbit of which its original position in the zone
was its aphelion. If we assume that this matter could move
without resistance, its velocity would increase according to
the law of radii vectores until it reached its perihelion. And
if we suppose this matter to form a planet at its perihelion
position by encountering just sufficient resistance in surround-
ing matter to retain its perihelion-radius by deflecting it
from an elliptic to a circular orbit, this would represent the
velocity of the inner planet moving according to the law
of orbit.
We cannot of course presume that this is the real condition,
although it may represent its motive factors. The nebula
being gaseous, would resist the direct continuity of the orbit
of a condensed outer particle or aggregation of such particles,
so that they could only fall sunward in spiral paths, possibly
as flocculi ; and the whole system might possibly be more
nearly represented as a pressure system upon the new-forming
planet accelerating its motion than as a free motive one, but
the dynamic effects would be the same.
127. The Rotation of Planets. Assume a planet ring to be
detached from the sun's nebula, and that henceforth this is a
free elastic body revolving with tangential velocity in equi-
librium with the attraction of gravity upon it to maintain
its orbital position according to Kepler's third law. If the
H
98 NOTES ON THE NEBULAR THEORY.
rotation of the peripheral band from any cause were slower
than this, it could not leave the sun's surface. If it were
faster its matter would fly off into space ; or, putting the
matter practically, the zone-ring would contract or expand
to its position according to the law of orbit. As regards the
separate parts of the planet ring, it is assumed that these
being at first a part of the sun's nebula in a highly gaseous
condition would revolve in all parts in relatively static
positions, exactly as though the ring were a solid body
attached to the solar nebula. This is inferred from the fact
that any intermotion of its interior parts in a gaseous body
would be more frictional than that of equal angular velocity
in which there would be no internal displacements.
128. If therefore we assume that the planet ring revolved
at first with equal angular velocity in all parts in mean
gravitation-equilibrium for its distance from the sun centre,
and that a condensation occurred in any part of the ring from
pre-existence of a denser part which may have been caused
by the intrusion of a comet, a shower of meteorites or other-
wise, then all parts of the ring-system sufficiently near
together to support a system of cohesion in gravitation-
continuity would be drawn towards the denser part with
velocity of approach inversely proportional to the square of
the distance from the gravitation-centre less the resistance by
friction within the system. In this case the tangential
velocity of the ring being assumed to be at its outer surface
in equation with gravitation for a circular orbit, there would
be no tendency for the ring to leave its orbit, but matter
would be continuously drawn towards the centre of attraction
of the new-forming planet, in which case accommodation
must be found for the volume of matter set free from its
outer zonal position and attracted towards the new-forming
planet.
129. Under the conditions proposed, we should have
towards the planet's nucleus currents from different parts of
KOTATION OF THE PLANETS. 99
the ring-system which would resemble in a certain manner
similar currents in the atmosphere which find accommodation
in cyclonic action in revolution about the centre of inertia of
the motive system, as originally suggested by Descartes. In
this manner the cohesion of the nebular ring would, in
condensation under the circumscribing cyclonic action, tend
to produce a rotatory nebular globe conserving a large part
of the momentum of the original uniform angular motion it
possessed in the former nebular ring when it was attached to
the sun, and all the active gravitation forces brought about
by its condensation towards the sun, deflected as they must
necessarily be for accommodation of space within the new-
forming planet's nebula.
130. If we assume that all parts of the planet ring con-
served the momentum due to the equal angular velocity at
the period the ring left the sun's nebula which we are
bound to do, or to account for the dissipation of this energy,
the rotation of the planet finally formed ought to be
consistent with the linear velocities of its parts. Under these
conditions the periphery of the planet when formed should
rotate with linear velocity equal to the excess of linear
velocity of the outer part of the nebular ring over that of
its inner parts. This proposition may be discussed by the
aid of a diagram.
131. Let a a" a!" (fig. 13) be a part of the outer circum-
ference of the nebulous ring, b b lr b 111 the inner circumference
towards the sun, and assume these circumferences to be
bounding-planes of matter contracting towards the planet in
the direction represented by a" to a' ', b" to b f . Let a" to b"
be any small arc section of the nebular ring. Then the linear
velocity of matter falling to a! being impressed upon a"
assuming a' to a" moved with angular motion equal to that
of the sun's centre, and a" to be condensed upon a' would
set the planet in rotation with velocity proportional to the
excess of the momentum of the matter condensed into the
H2
100 NOTES ON THE NEBULAR THEORY.
inertia of the portion of the planet formed at the time. The
condensation of matter from # x/ , when the linear velocity was
less than the angular velocity of the planet at a' b 1 in relation
to the sun, would impress its momentum at b' in direction
opposite to that of a' ', so that this would proportionally rotate
the planet in the same direction as the outer matter from a!'
Fig. 13.
to a'. Now if all parts of the ring by accommodation con-
served the momentum in condensation due to difference of
length of arc and that due to attraction of the parts of the
system upon themselves, by w r hich the axis of the planet
would be set in rotation by cyclonic action, the final velocity
of rotation of the planet would be approximately such that its
periphery would possess a velocity equal to the differences of
the velocities of the inner and outer parts of the nebular ring
a a 11 a'" and b b" b' 11 , between which it was formed, upon the
conditions of this proposition.
132. It is assumed that a planet upon final condensation
from a nebular ring will be placed very near the interior of
the ring, since radiation into space, as before stated, can only
take place from the outer parts, and not towards the nebulous
sun, which at an early stage of the planet's formation would
be heated sufficiently to maintain a nebulous state and be
nearly as large in diameter as the inner surface of the ring.
The nebular matter being continuous in the ring, will
maintain cohesion or separate by flocculation in attraction
towards the planet, as before stated, during its formation;
KOTATION OF THE PLANETS. 101
so that the exterior condensation may be represented as
showers of rain-drops falling upon the planet, carrying with
them the tangential impulse due to their original motion and
former position. This would occur so long as the interior
heat of the system could maintain a purely nebular state. If
the whole system was falling to the critical temperature of
liquefaction of a large part of the nebula ( 94), or the for-
mation was influenced by a ring of exterior heated matter, as
possibly was the case with planets interior to Jupiter, the
regularity of condensation proposed above would be materially
modified.
133. To maintain the condensation continuously in a
nebulous state from the zone-ring to the perfect planet, we
must evidently possess a large volume of nebulous matter in
this ring, as any thinly distributed system would condense
quickly by radiation of its heat after separation from the sun
into discrete matter, before a nebulous planet could be
formed. Therefore it becomes probable that only the large
planets of our system, Jupiter and Saturn, could condense
under purely nebular conditions wherein the equal angular
velocities of the system might be maintained. Further
inference that these planets are of purely nebulous formation
is found in part from their low specific gravity, due probably
to the conservation of heat in their interiors, resembling in
a certain degree the conditions of condensation of the sun.
134. Rotation of Jupiter and Saturn. Taking the planets
Saturn and Jupiter under the purely nebulous conditions
proposed, let r and r be respectively the outer and inner
radii or distances from the sun of two consecutive planets ;
then rri will be the diameter of the nebular ring which we
may assume as a gravitation system of circular cross-section,
as shown fig. 9, p p' (p. 67), from which the inner planet will
be formed, and 27r(r TI) the difference between the circum-
ferences of the outer and inner parts of the ring. Let P be
the diameter of the planet, and ?rP therefore its circumference,
102
NOTES ON THE NEBULAR THEORY.
and H the number of sidereal hours in one complete revolu-
tion round the sun. The peripheral space that the equatorial
surface of the planet will describe for its orbit in time will be
T)TT
2 T r, and the theoretical term H 1? according to this
proposition, will be
PH
= H 1 . The following table
constructed upon these data will give the theoretical rotation-
time in hours proposed approximately for a planet of equal
density throughout formed from gaseous matter moving with
equal angular velocity, upon this hypothesis. The T column
is the observed time in hours as far as known.
135. It is seen that the virtual velocities of the parts of
the condensation would depend upon their final position in
relation to the centre of the planet. The nearer the centre
the greater the angular motion impressed upon the planet
from an equal linear velocity, so that a planet dense at its
centre, and the reverse at its periphery, would upon final
condensation have greater rotation-velocity than one due to
the condensation of equally dense consecutive shell-layers
over its surface to form its mass. In the following table the
planets are taken as being of uniform density throughout.
Table of Theoretical Rotation of Planets formed under
purely Nebular Conditions*
Planet.
Difference of
circumference of
ring 271-0--^).
Circumference
of planet
X hours =7rPH.
Theoretical
diurnal
rotation Hj.
Observed
diurnal
rotation T.
Jupiter ...
2,489,000,000
27,670,000,000
11-126
9-868
Saturn . . .
5,534,000,000
56,896,000,000
10-27
10-16
Uranus ...
6,224,000,000
76,925,000,000
12-34
136. In the above table the acceleration of rotation or of
ROTATION OF THE PLANETS. 103
orbit due to the gravitation of exterior matter falling to a
nearer position to the sun is not calculated, as this may be
taken up in acceleration of the planet's orbital motion, as
before proposed. In the last column Jupiter appears of
greater rotation-velocity than the theory demands unless it
increases in density towards its centre ; it would therefore
appear, if the hypothesis given be strictly true as regards the
only factor of motion, that the density of this planet must
increase greatly from its centre to its measured perimeter.
According to this hypothesis, to give a velocity of rotation
of 9*868 hours for a planet of equal density throughout, its
diameter should be only 75*248 miles. If it is partly solid
and partly gaseous this number may express the diameter at
mean density. It may be its diameter in four millions of
years hence. Further the whole system of the planets may
have been derived from nebular zones which at a period of
early formation extended much beyond their present orbits,
so that the planetary system may have contracted throughout
its entire extent. This contraction would .give excess of
rotation beyond that resulting from the principles discussed
above, even assuming a part of the energy may have been
lost in the friction of planetary formation.
137. Although all difficulties with respect to acceleration
of Jupiter's rotation upon the theory proposed may be removed
by the suggestions given above, at the same time there is
no doubt that the observations of the surface of this planet
are very perplexing. The surface appears to be in violent
agitation. It is not entirely improbable that this planet,
quite recently as measured by astronomical past time,
possessed a ring-system similar to that of Saturn. This ring,
through some disturbing cause, the intrusion of a comet or
other matter, was probably thrown out of gravitation-equili-
brium, and the ring-matter, having stronger attraction to
the body of the planet than to the parts of the ring so as to
draw them together to form a satellite or satellites, the
104 NOTES ON THE NEBULAR THEORY.
separate parts of the ring are now drifting in concentric
orbits upon and around the planet with greater velocity than
that of its surface. In this case the heat engendered at the
surface of the planet by condensations or collisions of meteoric
matter projected thereon would produce a nebulous atmo-
sphere permitting only the approach of the exterior meteoric-
ring matter, which is probably in the form of dust, to drift
under the resistance it encounters in spiral or cyclonic paths
about the planet's equator and outward from it. This may
produce the present surface appearance, which may be similar
in motion to cyclonic areas in the atmosphere about our
equator. The virtual velocity of the parts of the broken ring-
being greater than that of the surface of the planet, this
matter in drifting over and covering the surface of the planet
would present the only measurable part open to our observa-
tion, the planet itself being entirely obscured.
138. In Jupiter we have not the low density which we
have in Saturn to indicate formation under purely nebular
conditions, so that the reasons given in the two previous
paragraphs are quite sufficient to account for the excess of
velocity over that required by the theory of our table. If
necessary, it would not be difficult to find others. If the
zone-ring was originally elliptical, and the planet condensed
at its perihelion position, the difference of linear ratios of the
outer and inner surfaces (fig. 13, a a, b b) would fully account
for the excess of rotation. Again, it is not impossible that
exterior matter moving at greater velocity drifted into the
planet during formation.
139. In the planet Saturn we have evidence of purely
nebulous conditions in formation, in which the surrounding
equilibrium of matter was so perfect that central rings of
condensed free matter were possible of formation round its
equator. In this case we have a rotation period in nearly
exact equation with the tangential velocities of the part of
the exterior nebula from which the planet was formed upon
ROTATION OF THE PLANETS. 105
the theory proposed. Nevertheless it must be in some degree
accidental that this comes so nearly into agreement with my
theory in this planet. It is in all probability much more
dense in its central parts than at its periphery ; it should
possess, therefore, greater velocity than it does, but this
difference may well represent the friction of the system in
formation.
140. Further, with regard to Jupiter and Saturn, it is
quite uncertain whether we make sufficient allowance for
in measuring such bright bodies as these planets.
The mean measurements of Venus as a bright body by
Hartwig, Kaiser, Airy, and Ambronn give H /f '593 at a
distance equal to its mean transit-position. The measurement
of Venus by Auwers as a dark body in transit gives 16^'SOl,
from which we may conclude the true measurement of Venus
is probably 17 // *197 ; applying a similar reduction to Jupiter,
which it is impossible to measure in the same manner, we
have its diameter about 80,000 miles. This proportion is also
confirmed by some measurements made by myself of the
iridescence of bright bodies under the microscope. It is
evident also in the apparent thickness of the filament of an
incandescent electric light, that may be compared with its
reflection in a polished surface of black glass, which suggests
a possible mode of measurement of Jupiter and Venus by
reflection from a black surface.
141. Uranus is added to the table, which gives, upon the
theory of the rotation of Jupiter and Saturn, a period of
12*34 hours. This planet, however, if we take the direction
of its satellites as an index, is moving probably, but not
necessarily, in the reverse direction, which might occur from
its formation from discrete particles, according to the theory
of Faye *. This theory may be shown by the same diagram.
In this case matter is assumed to be moving in free orbits
* Faye, < Sur 1'Origine du Monde,' 2nd edit. p. 117.
106 NOTES ON THE NEBULAR THEORY.
round the sun, and the particles along the arc (fig. 13, a, a! a ff )
assumed to have less virtual velocity than those along b b' b",
consequently the planet would move in the reverse direction.
Another plan of rotation will, however, be suggested further
on.
142. Rotations of the Asteroids. The rotations of planets
inferior to Jupiter would, of course, depend upon the mode
of their formation. The attenuated plane of the nebula pro-
posed for the formation of the Asteroids would leave these
condensations about this plane so as to form an early break
in the nebular system of the sun, and the henceforth separate
nebular system of Jupiter ; so long as the Asteroids remained
in the orbits of their original formation, they would take
rotation periods consistent with the principles proposed for
the formation of purely nebulous planets considered above,
little affected by the decentralizing action of Jupiter or its
original ring-system. Any of these minor planets, if formed
through separate condensations of concretions of smaller
planets, or of meteoric matter by after collisions, in the
crossings of orbits, would have their original rotation due to
condensation under nebular conditions diminished by the loss
of the directive-momentum of rotation, which would be
converted into heat at the time of collision. The absolute
condition of these bodies must remain altogether speculative,
our present limited knowledge being insufficient to obtain
data for the actual rotation-periods necessary for its con-
sideration. They most probably move with different rotation-
velocities, and it is not improbable that some rotate in the
reverse direction.
143. Mars. If Mars was formed directly under the
nebular conditions proposed for the superior planets, from a
nebular ring which extended to the near asteroid ^Ethra, it
would possess a rotation only slightly in excess of its revolu-
tion-period. If we assumed a wider area for the ring, possibly
to include the formation of 2Ethra in another or opposite part
KOTATION OF THE PLANETS. 107
of the same zone-ring, we might theoretically give the
rotation-period of Mars its actual or any value we please up
to or beyond that of Jupiter. It is, however, probable that
other than purely nebular conditions influenced the formation
of this planet. Mars, the Earth, and the inferior planets
possess a density-system which very probably indicates con-
tacts or collisions of solid matter to form the interior parts.
Therefore the nebular conditions proposed for the superior
planets of low density do not hold entirely for index of
rotation-period in this case for planets of high density, as it
would be considerably modified by the discrete mode of
formation.
144. Laplace suggested that a nebular zone-ring would
break up into many parts, which would draw together and
form separate nebular globes. These being formed at slightly
varying distances from the sun, would finally coalesce and
form a single nebular globe. In so attenuated a system as
the zone of Mars would be upon this theory, such nebular
globes as may have been produced by early condensations
would probably be condensed by radiation, before union could
be effected into a single globe. Therefore the separate globes
or units of condensation might at a certain period be repre-
sented by a band of planetoids formed by condensations in
different parts of the original nebulous band, these planetoids
being formed within the band at only slightly varying dis-
tances from the sun. If the orbits of the separate globes were
elliptical and of nearly coincident period, they would con-
stantly approach in opposition, come into collision, and by
cementation, in which a certain amount of heat would be
developed, produce finally after cooling the diversity of
surface we observe upon this planet. It is possible that this
form of collision may again occur at a definite calculable
period with the near asteroid .ZEthra.
145. The rotation-period of Mars, as of other planets, must
necessarily represent the sum of the directive momenta of
108 NOTES ON THE NEBULAR THEORY.
the factors of matter which formed the planet, and this might
be fixed upon purely nebular conditions as with the planets
Jupiter and Saturn, allowing time for the nebula to con-
tract upon the sun only, without planet-formation as before
proposed. The general conditions of density of the surface-
formation of Mars and the presence of near Asteroids do not
indicate equable nebular conditions at its formation. This
does not, however, infer that it was not at one period partly a
nebulous globe, the gravity of which was superior to that of
any near body of condensed matter ; indeed, this is probable
for the formation of satellites upon principles to be discussed
further on.
146. Rotation of the Earth. If we take the same purely
nebular conditions as proposed for the formation of the
large planets by the condensation of matter carrying virtual
velocities of the parts of the ring-system to the planet, and
assume under like conditions that the earth's nebula ex-
tended at one period to the orbit of Mars, we shall arrive at
a rotational velocity much greater than that which we observe.
But in the discoidal nebular system proposed, fig. 10, p. 85, it
would be extremely improbable that the actual earth-forming
nebula in contact with it ever possessed this radius. By
the principles of sun-condensation without planet-formation
already discussed, and its condensation when matter just
interior to its orbit was at a critical temperature, we may fix
the earth's nebular ring-orbit consistent with its period of
rotation, as before, by the formula -p-a- , considering the
density of the earth and a certain extent of space between its
orbit and that of Mars for its volume. The probability is
that the greater part of the Earth-Mars interspace was
condensed at an early period into separate smaller nebular
planets, as just proposed for Mars, and showers of meteorites
at its outer parts were moving in very elliptic orbits. The
condensation which may represent the nucleus nebula of the
ROTATION OF THE PLANETS. 109
earth-moon was possibly at about its present mean radial
distance from the sun. Under these conditions the iouter
condensations, whether nebulous, liquid, or solid, assumed of
eccentric orbits, would be drawn at perihelion towards and
into the earth's nebula, if these discrete condensations at the
period extended, as was probably the case, beyond the radius
of the moon's orbit. Further, in an attenuated ring-system,
as the earth's system may have been at an early period, while
rapidly cooling, condensations would occur at different parts
of the ring, and at slightly varying distances from the sun,
as before suggested, so that ultimate collision must occur
between them and the earth. Under such conditions we
should have through condensation variety of density and
surface-conformity, and rotation in composition with all the
motive factors of the earth's formation. The development of
heat under the process of formation may have maintained a
considerable nebula round the earth at an early period, but
not being an entirely nebular formation its motion of rotation
would be much slower than that calculated for Jupiter and
Saturn if taken under purely nebular conditions. This
matter will be reconsidered in detail further on.
147. The rotations of Venus and Mercury would be subject
to the same conditions as that of the Earth and Mars. How
far these planets may be formed from nebular or from discrete
matter it is impossible to say. If formed from nebular
matter, the motion would be greater than that of the Earth
actually. If formed from discrete matter, produced by the
general lowering of the temperature of the surrounding
nebula to its critical temperature, it would be less ; or these
factors might act conjointly, so that the rotation might
be nil.
CHAPTER VIII.
REVOLUTION OF SATELLITES. DIRECT MOTION. ROTATION
OF THE MOON. RETROGRADE MOTION. COMPARISON OF
THE REVOLUTION OF THE MOON WITH THE ROTATION OF
THE EARTH FROM NEBULAR CONDITIONS.
148. Revolution of Satellites with Direct Motion. In the
revolution of satellites around their primaries under purely
nebular conditions, no other law could hold for the conden-
sation of nebular matter than that which must hold for
condensation upon the primary ; so that, if the motion of the
planet's perimeter were equal to the difference between the
linear velocities of the inner and outer parts of the primitive
nebular ring from which it was condensed, the satellite's
revolution should be consistent with this under the same
mode of formation. Thus, taking the satellite's distance and
revolution period, the virtual velocity of the satellite should
equal the difference of rates of the extreme parts of the ring,
previously expressed as 2?r(r r^). At the same time this
must be taken as representing the angular motion of the
entire exterior nebular system within which the satellite or
satellites, or any ring-system, as in the case of Saturn,
were formed. As soon as the satellites were formed,
the condition given, 127, for planet formation must hold
in the condensation of an attenuated system about the
planet. The motion and position of the satellites, if there are
more than one, must finally rest in relation to the planet
according to Kepler's third law, the squares of the numbers
REVOLUTION OF SATELLITES. Ill
representing their periodic times varying as the cubes of the
numbers representing their mean distances, subject to such
influences as the sun's attraction may produce upon the
system. Under these conditions, the energy of the equal
angular velocity of the original nebular ring may be split up
into factors represented by the separate satellites and the
general equality of the original angular velocity be lost,
while retaining the mean momentum of the original sur-
rounding nebular system about the planet. So that, in a
purely nebular system not previously locally condensed, we
ought to find the momentum of the angular velocity of the
primitive nebula fairly represented in its entirety in the
central system of the planet and all its satellites. Further,
under these conditions of nebular or gaseous formation, the
motion of the satellites must be direct with respect to the
planet. Therefore it cannot include the systems of Uranus
and Neptune, wherein the motions of the satellites are retro-
grade. This leaves us for consideration only the outer
planets, herein presumed to be formed under purely nebular
conditions, which have direct motion, or, more particularly,
the satellites of Jupiter and Saturn. These satellites, as
before stated, under the conditions given, cannot be taken
individually, but as a mean of mass and motion of the whole
contained in one system.
149. Revolution of the Satellites of Jupiter and Saturn.
Under the conditions given, let 2?r(r rj represent the
mean momentum of the nebular ring active upon condensa-
tion in forming the planet and its satellites. Let
where S represents the diameter of the orbit of the satellite,
H the hours in the sidereal year of the planet, and Hj the
hours in one complete revolution of the satellite round its
planet. In this manner, the revolution of the satellites of
112
NOTES ON THE NEBULAR THEORY.
any system in the aggregate should agree with the angular
rate of motion of the equator of the planet, and this with the
momentum of the nebular atmosphere surrounding the planet
from which the whole system of satellites is assumed to be
formed. As experiment, we may take each of the satellites
of Saturn and of Jupiter to be formed of equal quantities of
nebular matter at about their present positions separately, and
divide by their number so as to find the mean place of the
imaginary satellite we desire to consider as the unit of the
system. The result of this is shown in the following table :
Table of mean Rotational Velocities of Satellites.
Mean position of
TrSH
5T"
2*r(r-r 1 ).
Difference.
Saturn's satellites and ring
Jupiter's satellites . .
5,264,300,000
2,777,450,000
5,540,100,000
2,490 950 000
- 275,800,000
+286 500 000
150. We see again in this an excess of velocity in the
satellites of Jupiter which is consistent with the excess of
motion over that derived from 27r(V r { ) observed in the
planet. This may infer an intrusion within the nebula
previous to the formation of the planet of a large mass of
matter moving with greater velocity, but so as to produce the
same direction of rotation as that of the original nebular ring,
as before proposed, which is again consistent with Jupiter's
greater motion and abnormal mass. The difference shown,
however, is made much less by taking the mean motion of
the satellites in conjunction with their masses, the outer
satellites of Jupiter being of fgreater mass than the inner
ones. And in the same manner the mass of Saturn's rings
exceeds that of its satellites, so that this difference would be
OTT
again diminished, and would come as fairly to my
REVOLUTION OF SATELLITES. 113
theory as the conditions probably would admit of calculation
in a system wherein there may have been intrusion of exterior
matter, cometary or other, during the formation.
151. Satellites of Mars. These small bodies move at a
higher velocity than the equatorial surface of the planet. It
is therefore clear that they could not have formed a part of
a nebular system moving at equal angular velocity with the
planet, assuming the planet was entirely condensed from the
nebula and moved originally only at its present rotational
period. By the condensation of a nebular zone as defined
above for the satellites of Jupiter and Saturn, the rotation
periods of the satellites of Mars would be made consistent
by treating them as revolution systems, 127. It is clear,
however, as before suggested, that we have not in Mars a
nebulous condensation of the kind that we have in the outer
planets, where the condensation has produced a mass of
small specific density. The probability is that the nebula of
Mars possessed at a certain period a rotation consistent with
the revolution of its satellites, but that the planet was of
smaller mass, the whole system appearing as a planetary
nebula. That about this period the planet entered into col-
lision with one or more planetoids of smaller mass than itself,
which were previously condensed to solid form. These plane-
toids may have penetrated its nebulous atmosphere without
materially changing its rotational velocity, but have reduced
that of the planet upon collision. Such collisions would
develop great heat, partially liquefying the solid planetoid,
and produce by cementation with it a partial protrusion
of matter beyond the sphere, in which we have an index of
the surface configuration. In this manner, the momentum
of the outer parts of the nebula would be maintained, although
the penetration by a planetoid to the centre would possibly
cause sufficient disturbance of equilibrium in the nebula for
the satellite-zone to immediately commence the formation of
the satellite.
114 NOTES ON THE NEBULAR THEORY.
152. The orbit-position of a satellite can only follow
Kepler's third law. In a satellite-zone open to a system of
condensation at the outer radiation-surface of its nebula
moving at equal angular velocity, in which refractory matter
of the outer nebula condenses first, the condensed units will
move through the resistance of residual gas under the influ-
ence of gravity in spiral lines, until they reach the central
condensation, unless an orbital velocity position is found
according to Newton's Law * ; and in this position the
satellite must be formed. Therefore a satellite may be formed
at any distance from its planet. If matter falling upon a
planet possesses less tangential momentum than that which
produces orbital velocity at any position above the planet's
surface, satellite formation would be impossible as such matter
would fall to the body of the planet.
153. The Moon possesses a higher virtual velocity than the
equatorial surface of the earth in the proportion of 2288*43,
the moon's mean hourly motion, to 1037'6, the hourly motion
of the earth's equator. Assuming the earth system to have
been entirely nebulous, and the nebulous matter to condense
in equal shell-layers over the earth, commencing from the
time of the condensation of the moon from gaseous matter,
decreasing in density inversely as the square of the distance
from the earth's centre ; then the earth should possess nearly
the same initial velocity at its equator as that of the moon in
its orbit, assuming no friction of formation developed into
heat upon the earth's surface at the time. In many ways
this is improbable, as the whole system does not confirm the
earth's formation under entirely nebular conditions. It is
therefore probable that the earth's nucleus was a considerable
liquid, or partially solid, mass before the time of the moon's
early condensation. Further, the configuration of the earth's
surface indicates that it was probably formed in part by
* ' Principia,' Lib. ii., prop. xv.
REVOLUTION OF SATELLITES. 115
concretion of planetoids or meteoric matter projected from
exterior space into its nebular ring, which retarded its
velocity and disturbed its axis of rotation. Either of the
above-stated conditions, independently of the friction of
formation or of tidal friction, if this may be included, would
fully account for the earth's minus rotational velocity com-
pared with the linear velocity of the moon, which must
necessarily follow the law of orbit. At the same time it is
highly probable that the nebular system of the earth extended
much beyond the orbit of the moon at the time of the com-
mencement of the moon's condensation *.
154. The rotation of the moon taking place in exactly the
same time as that of its revolution round the earth, infers
that the condensation of the moon was at first into a complete
narrow ring, probably liquid at one period, therefore moving
in all parts at equal angular velocity to the earth. If it
condensed as a globe from a wide vapourous ring moving
in all parts at equal angular velocity, as previously proposed
for the outer planets, it would then possess a direct motion in
rotation in excess of its revolution period. If it was formed
from local condensation at first into discrete nebular matter,
it would possess a reverse rotation f ; combination of these
factors, direct and reverse, might give its present rotation,
but the proposition of the early formation being a narrow
ring appears to me more probable to bring about the exactly
equal periods of rotation and revolution.
155. The condition of condensation in rings which after-
wards formed satellites appears to be difficult of conception
to some astronomers. This must be so, if the density of all
parts of the ring is assumed to be uniform, as it appears to
be approximately in the rings of Saturn. But this system of
equilibrium appears to be exceptional; if the rings move at
* See the Author's paper, Brit. Assoc. Reports, 1885, p. 915.
t See Faye's Theorem, ' Sur TOrigine du Monde/ p. 117.
12
116 NOTES ON THE NEBULAR THEORY.
orbital velocity, the equilibrium of its matter from tangential
momentum and gravity is such that, irrespectively of its
rotation, its matter may be considered to float on a frictionless
plane ; so that the initial gravity of its mass acts directly
upon itself. Therefore, if the nebular moon-zone were
unequally distributed, its condensation would be direct to
the densest part.
Suppose the condensed zone represented by fig. 14 a, then
its point of tension would be at x. Assume this point to
separate by the initial slow action of the entire gravity of the
ring. Then its matter near the point of separation would
gather into two semi-globular terminals, fig. 14 b, x'. Initial
Fig. 14.
gravity would now act in opposition to the direct momentum
of the mass, accelerating the velocity of the limb b and re-
tarding that of c. So that at some point about d the ring
would condense into a globular mass, by its extreme conden-
sations coming together.
156. Retrograde Motion of Satellites. The conditions
proposed for the direct motion of the satellites previously
considered as derived from the condensation of the gaseous
nebula, could not possibly hold upon the hypothesis given for
the satellites of Uranus and Neptune, which move in the
retrograde direction. It may appear, so far as the direc-
tion only of this motion is concerned, that this would be
demonstrated by the theory of M. Faye, 141, as due to their
KETROGRADE MOTION OF SATELLITES. 117
formation from discrete matter, the satellites being condensed
from a ring of such matter, every particle of which was
originally moving in a free orbit in gravitation equilibrium ;
this theory may possibly be applicable to the satellites of
Neptune. There are, however, many peculiarities about the
satellites of Uranus which do not admit of this hypothesis.
They move in orbits inclined nearly 80 to the planet's orbit-
plane, so that the differences of velocity of the parts of the
orbit of any assumed nebular ring or matter caused by the
differences of distance of its parts from the sun would be
very small. These conditions would, therefore, cause the
satellites to revolve at a very slow rate, that is, at about
2^0 f that observed. We must, therefore, certainly look
for additional causes for which other suggestions may be
offered.
157. If discrete matter was formed at the limits of the
solar nebula, when this was moving at less than orbital
velocity, as before supposed, and the early discrete matter
was formed of the more refractory matter so as to leave the
more attenuated, less refractory nebula to form a resistance
to the centralizing condensation of the discrete matter, then
this matter might carry the momentum of its former angular
velocity to the inner, denser nebular matter which formed the
sun at the time, leaving the residual matter slowly condensing
at less angular velocity. Such a system would produce a solar
nebula moving at higher velocity than its peripheral lighter
outward parts. I have endeavoured to show in my work upon
Fluids* that every fluid system in rotation, cyclonic or other,
engenders in the surrounding fluid or medium which offers
resistance to its direct motion an opposite direction of motion
of rotation around its borders. By this action the central
rotating fluid attains a kind of rolling contact upon the
* * Experimental Researches into the Properties and Motions of Fluids,
1881, p. 224 et seq.
118 NOTES ON THE NEBULAE THEORY.
surrounding, more static fluid, which produces by this mode
of rotation the least frictional resistance to the motion, in
what I term friction-whirls to the direct flowing system.
Upon this principle, if the central system in this case were
condensing the more refractory pneuma into nebula with
increase of angular velocity by the effects of gravity, then the
surrounding, less refractory pneuma, less motive in the
direction of the central system by the resistance of surrounding
matter not moving at equal velocity or possibly in the same
direction, would offer a certain amount of resistance at the
periphery of the central condensation of nebulous matter.
This is shown by the lateral form of motion to a current, fig. 5,
p. 44 ; it may possibly be better explained by a diagram.
Let one plane of the interstellar space, subject to the superior
Fig. 15.
attraction of our sun, be represented by the circumscribing
outline N, fig. 15, along which line the sun's attraction is
assumed to be in equation with that of other near stars.
Let S be the centre or sun ; and let the central nebula be
bounded by the circle 0, the arrow near the line showing the
direction of rotation. Then in the space bounded by N on
one side and upon the other the matter would be less
motive than that of the central system ; and this would
RETROGRADE MOTION OF SATELLITES. 119
rotate U in the reverse direction, as shown by the arrow.
This form of motion is shown by many experiments in my
work on " Fluids " already quoted.
158. If the central system contracted by the influence of
gravitation and other conditions already discussed, say, to the
diameter represented by jt>, which we may take at the orbit
of Neptune, then the whirl system U would be also con-
tracting upon itself; and being also attracted by gravitation,
it would become a motive part of the solar system S, falling
into the same direction of revolution but with the opposite
direction of initial rotation, just as a roller or ball-bearing
moving between the surfaces of an inner and outer cylinder
progresses along the surface of the inner cylinder in its direc-
tion of revolution, but at the same time takes the reverse
direction of rotation. Upon this theory it may be inferred
that Neptune and Uranus were possibly perfect rotatory
systems of nebulous matter before they were incorporated
into the central or solar nebular system.
159. In the above construction, considering the inclinations
of the orbits of the satellites of Uranus, we have at first the
loss of directive momentum due to the differences of velocity
of the parts of any ring-system that could have formed and
rotated these satellites in the plane of the planet's orbit,
so that the surrounding matter in the satellite's orbit-plane
became more subject to resistance than if the planes of orbits
of the planet and satellite were nearly parallel. The motion
for reverse rotation under fluid resistance is active laterally,
exactly as in the plane of motion, and resistances are more
likely to occur exterior to the orbit-plane than in it. The
form of nebula at a certain period of formation best adapted
to produce the system of the satellites of Uranus, is possibly
that of y I. 176 in Coma Berenices, where the nebula appears
to turn up at one terminal at a considerable angle to its mean
plane of rotation.
160. Under the same principles as given in the above
120 NOTES ON THE NEBULAR THEORY.
hypothesis, it may be suggested that the contact form of
reverse rotation may have been produced in a nebular con-
densation having either no rotation or a reverse rotation,
being attracted into the sun's nebula. Such a condensation
may have occurred in an interspatial position between the
nearly equal attractions of several stars, as, for instance,
in the position outwards between b and of or a and b 1 of
fig. 11, p. 88. If a nebula so formed drifted by small excess
of gravity towards our sun when it was in a nebular state,
it would enter the frictional system of the borders of the
attenuated solar nebula. The inertia of the newly introduced
planetary nebula would resist the rotation of the solar nebula,
which would therefore produce a motion of rolling contact in
the meeting-plane between the two systems, as before sug-
gested, as the least frictional form of fluid motion. In this
manner a kind of wheel-and-pinion motion would be induced,
in which the smaller planetary nebula would represent the
pinion moving in a reverse direction to the solar nebula
wheel.
CHAPTER IX.
COMETS CONSIDERED AS ORDINARY GRAVITATIVE MATTER IN
ROTATION CONSTRUCTIVELY AS A PART OF THE PLANETARY
SYSTEM.
161. If we can accept the idea of a universal pneuma,
23, and that this pneuma was motive in rotation, separating
and condensing into separate systems, 43, a condition of
original motion in matter that may not be unlike that pro-
posed in the theory of Descartes and Faye * ; then all separate
parts of the system must continue motive under condensation
to take up the general momentum of the system.
162. If we consider the relatively small volume that would
be circumscribed by our solar nebular system, if taken to be
in its original nebular state of spheroidal form at a period
when it was circumscribed within the orbit of Neptune, as
compared with the mean distance between our sun and the
nearer surrounding stars, we find what a relatively small space
the orbits of our planets occupy. So that if the original
pneuma at its earliest period extended to the mean of inter-
stellar space about our sun as suggested, we can only imagine
that many millions of local condensations due to exterior
radiation were formed in exterior parts of the system. These
condensations would afterwards only slowly drift sunward,
but they would still carry with them the same factors of
original rotative influences and the influence of the attraction
to near-surrounding matter, as before discussed, 70.
163. Therefore, taking the original pneuma system as shown
* <Sur POrigine du Monde,' 2nd edit. p. 101 et seq.
122 NOTES ON THE NEBULAR THEORY.
in one imaginary plane, fig. 8, AB (p. 59), extending to the
mean distance of our sun and a near star, we can but imagine
that at an early period there may have been many millions of
local rotatory systems of matter condensed to a nebular con-
dition in a free state, which would be moving from the outer
pneuma system from the positions a, 6, c, d sunward by central
attraction. We may group such systems together as comets.
164. In the above construction we may suppose that the
cometary system was the earliest prevailing system of the
outer condensation of matter ; that the comets which were
formed by local condensation to nebulae were most generallv
absorbed into the solar-planetary system when this was of
immense volume ; so that at a certain period our solar system
would have appeared, if viewed from a great distance, as an
immense floccular system wherein the exterior cometary
condensation would appear incandescent from friction and
electrical excitation within the interior nebular condensation,
and from intense chemical action in the condensation of the
pneuma to nebula. These flocculi would be drifting sunward
by the effects of their attraction and the small resistance of
the surrounding attenuated pneuma in spiral paths, similar
to the spiral nebulae 31 M, 81 M, 56 $, 168 $, &c., as
before proposed.
Another condition that must mark the formation of comets
considered as exterior condensations of the pneuma system,
is that tne direction of orbits must have been influenced by
the gravitational effects of the larger mass condensation
forming at the time upon the scheme proposed in 83 and
illustrated by fig. 8, p. 59. Therefore, comets must have
been formed in many cases in series, from attractions a, b, c, d
of this figure, taking one orbit-plane, but with varying
eccentricities of orbit, depending upon the amount of original
tangential impulse each comet possessed upon starting sun-
ward, as the conditions entail.
165. Upon these principles the comets and cometary matter
.; FORMATION OF COMETS. 123
we possess at the present time in our ancient solar system
represent only the waifs and strays formed by exterior con-
densations which have escaped absorption, that have arrived
from interstellar space after the sun had condensed to nearly
its present volume, 68. The relatively small number that
remain may also, through the disturbing influences of the
antagonism of initial centralizations and solar attractions,
hereafter experience internal strains and collisions within their
systems about perihelion which may cause their disintegration
or deformation, so that they may be lost to astronomical
observation in the future, under conditions to be discussed.
166. Although the earlier condensations of pneuma to
nebula exterior to our motive solar-planetary system would
produce, upon conditions discussed, rotatory systems of nebulae,
we can scarcely imagine that such nebular conditions could be
generally maintained in exterior matter until the present time
under the excessive radiation of their original heat into space.
Therefore, we have the extreme probability that cometary
matter is at the present time largely condensed into solid small
units of meteoric or planetary matter.
167. The theory of association of comets with meteorites
is as old as Anaxagoras, who states that comets are the con-
gregation of wandering stars that approach so near to each
other that they appear to touch *. This theory, for certain
factors of cometary existence, is greatly strengthened by the
discovery that our known meteor-streams follow in the orbit
of certain comets, as pointed out by Schiaparelli for the
August meteors, and for other meteor-streams by Oppolzer,
0. F. "W. Peters, Prof. Newton, and others, which theory is
also ably supported by Prof. Lockyer f.
Under this theory the difficulty of finding cause for the
self-illumination of such streams, if they form comets, is very
* Stanley's < History of Philosophy,' p. 64.
t Astr. Nach. No. 1384. Lockyer's Meteoritic Hypothesis/ p. 138.
124 NOTES ON THE NEBULAR THEORY.
great. Professor Tait has endeavoured to prove that such
meteorites would be subject to sufficient collisions among
themselves to account for the light * ; but if the meteorites
follow one another in streams, there must be very small
differences of velocity between them, and if they approach
one another, assuming them widely distributed miles apart,
their collisions must be very gentle, and produce very little
light, if any. Otherwise, the observations of Mr. Denning
upon the Biela meteors show that they possess great diffuse-
ness of radiation, so that their paths appear to diverge from
an area rather than from a point of the sky, indicating inter-
motion among their separate units.
168. There is another objection to the meteoric-swarm
theory which has not been attempted to be met, or even
suggested that I am aware of, which is, that the separate
units of the comet must, under the conditions of this theory,
necessarily follow Kepler's third law of orbital motion, that the
squares of the members representing the periodic times of the
separate meteorites must vary as the cubes of their mean dis-
tances from the sun. Therefore, assuming any comet to have
a tail of one million miles in diameter, as commonly observed
for the larger comets, the velocity of the outer meteorites of the
swarm must be very much less than that of the inner ones
nearer the sun. Under this condition, if the comet were a
swarm and at a certain period from some unknown cause of
the symmetrical form common to comets, as, for instance,
that of Halley or of the great comet of Sept. 1882, or
other, Plate III. A, i,j 9 as the parts of the swarm would be
actuated by various velocities, it could retain this form for a
short time only. So that on its return to perihelion, for
instance, it could only be represented at most by a scattered
band of meteorites spread over a great distance in space that
could never again appear as a comet. To take a self-evident
* Edin. E. Soc. Proc. 1879, p. 367.
COMETS OF LONG PERIOD. 125
case of the conditions in question, assume our moon at opposi-
tion to take a solar orbital motion without revolution around
the earth, then it is clear by Kepler's third law that we should
soon leave it behind us in space, so that it would become in
time in conjunction with the opposite part of our orbit.
Indeed the only condition possible for a meteoric theory in
which a comet can retain a symmetrical form, is that the
system of meteorites that form the comet should be in revolu-
tion about the centre of inertia of the system, moving in
elliptical orbits, in the same manner as the comet moves about
the sun and as satellites are in revolution about their planets.
This will be more particularly considered presently.
169. Comets of long period. The general principles of
direction of orbit from local condensations at a great distance
from the sun have been discussed, 71. We have now, there-
fore, only to consider the probable intermotion of the parts
of such distant condensations as may possibly produce comets
of the symmetrical form we observe in them upon planetary
conditions, and, therefore, such as are outwardly, as it appears
to me, evidently moving under the direction of symmetrical
orbital law.
In the extensive volume of pneuma considered as the
extreme field of comet-formation, which would be subject to
the influence of the near stars almost as much as that of our
sun, 76, the centralizing influence of gravitation would
have little effect in changing the natural formation of in-
dividual systems of matter after they were once constituted.
Therefore, assuming original motion in the pneuma such
as we have found necessary for the formation of our solar-
planetary system, 62, such motion must, as before stated,
have extended to all parts of the solar pneuma. If any original
isolated system, of large volume in its original state, were in
slow revolution with its parts moving at equal angular velocity,
then upon its condensation to a smaller volume its rotative
velocity would increase, as previously discussed for solar
126 NOTES ON THE NEBULAE THEOKT.
rotation, 116. This rotation of any part of the system would
be maintained in projection sunward, and if in free matter
projected from a great distance, it would form a comet of
long period.
170. Comets of short period. These possibly depended in
many instances for their orbit upon deflection of the matter
of the comets of long period by the influence of planetary
attractions. At any early epoch such long-period comets,
moving at high velocities by accumulated gravitation in
falling from a distant part of space, would fall into the solar-
planetary nebula or into any detached zone-ring of nebular
matter which may have been present at the time moving at
orbital velocity round the sun. In such a case the motion
of the comet would be retarded by the nebulous matter and
enter into composition with the motion of part of the zone,
or, if not incorporated with it, it would be deflected by it
from its original orbit into a less eccentric orbit. Comets of
short period would also be formed upon local disturbance at
any part of a planet-forming zone-system by a local condensa-
tion forming at a distance within the orbit-zone from the
position of the planet's condensation, which was at the time
beyond that of its prevailing attraction. Comets so formed
may be termed planetary comets, and bear relation to certain
planets, as Saturn, Jupiter, Mars. Short-period comets were
also probably formed by local condensations outside the mean
planetary plane at the same period as the planets were formed,
when the planet's mass was not the superior attraction with
respect to the position of condensation. They may also be
formed by the detachment of parts of the tails of long-period
comets disturbed at perihelion by disruption of the cometary
matter by heat, which retarded the revolution-velocity of a
part of the system.
171. Symmetrical elements of Comet-formation. I have
offered some general arguments for the construction and
motions of local rotative systems formed in space and pro-
SYMMETRICAL ELEMENTS OF COMET-FORMATION. 127
jected towards the sun by its superior attraction, as suggested
above, in a paper published in the 'English Mechanic' in
1883 *. These ideas will be now reproduced, with some
extenuations that appear to me necessary in reconsidering the
subject.
We can scarcely enter into the discussion of the motions
of comets without making a clear division of the subject as
to whether they have been derived from purely nebular con-
ditions directly, or have suffered from the attraction of other
bodies near which they have passed so closely as to have their
general motive symmetry destroyed. That this condition of
disturbance occurs is quite evident in the present state of
what was formerly Biela's comet, and in some comets which
have from unknown causes become invisible, and may now
only be represented by wandering meteoric systems, but
whose orbits were clearly defined upon their first appearance.
It follows, therefore, that for any symmetrical law of comet
construction we must take into consideration such comets as
retain the symmetrical form which we may suppose that they
possessed when originally projected from space. These comets
may be the only ones that are not under conditions of dis-
solution, which may be at the present time the more common
phase of comet life. If the comet depart through some
disturbance from its law of original construction, its matter
may present afterwards only what we may term a specialized
confusion, too complicated to discuss by the most advanced
science.
172. The symmetrical comets will be presumed to possess
elliptical orbits which have not been materially disturbed
from the time of their original formation and projection
towards the sun. Types of such comets may be found in
Halley's, Donati's, the great comet of Sept. 1882, and many
others of long period. They may be distinguished by possessing
* ' English Mechanic,' 22nd June, 1883.
128 NOTES ON THE NEBULAR THEOKY.
a head and forward projection of the coma of symmetrical
outline, after the manner of 7i, i, j, Plate III.
173. It has been fully demonstrated that the head of a
comet follows a truly elliptic or parabolic orbit ; so that we
have no doubt that this part of the comet is subject to purely
gravitational influences. The difficulty presented by these
bodies is that the tail has not conformed to the conditions
of orbit for the parts of a free system, or as it should do
upon the swarm theory. This point will now be particularly
discussed.
174. Comets considered as Gravitative Matter. The cer-
tainty that the orbits of comets conform to the laws of gravi-
tation was clearly laid down by Newton as a principle. This
would lead us to infer that they are composed of quite ordinary
gravitative matter, which is again to a certain extent con-
firmed by the spectroscope. The reason why it is thought that
there must be a deviation from this law (by Olbers, Bessel,
J. Herschel, and others who have followed this idea) is that
during the perihelion passage of the comet, the tail, which
must be considered a very material part of the cometary
mass, diverges greatly from the normal elliptic or parabolic
orbit.
175. To meet this case, we have been asked to assume that
the tail is unlike any form of matter with which we are
acquainted, that it must be antigravitative, or that it becomes
so from some cause at or near the perihelion passage of the
comet. It may be suggested that the law of universal gravi-
tation is one of the last we should abandon, seeing that it has
done such perfect service wherever our knowledge of the
conditions was exact. Further, there are other sufficient
reasons by which we may conclude that there cannot be
repulsion in any part of the comet, as the centre of gravity
of the cometary mass follows constantly in the true orbit.
For if a portion of the cometary mass, that is, the tail, changed
its state of constant attraction so as to become unlike other,
COMETS CONSIDERED AS GRAVITATIVE MATTER. 129
ordinary gravitative matter, and this portion became repulsive
from the sun by heat, electricity, or otherwise, when the
comet passed near perihelion, then the centre of gravity of
the cometary mass must be altered by this repulsion, and
would be displaced in relation to the sun's attraction ; so that
the sun would no longer occupy the focal point in the orbit of
the portion of the cometary mass that remained attracted to it.
Therefore, a new form of orbit must necessarily be formed to
suit the altered conditions of attraction, gravitatively central
to the mass attracted only, or there must be in this case a
deviation from Kepler's third law, a condition at least im-
probable. As regards the change of form or properties of
any known matter, so far as physical knowledge extends, we
may take it that heat has no effect whatever upon its ponder-
ability, so that difference of gravitation from this cause would
not be possible through the difference of temperature induced
in the comet by passing very near to the sun. Therefore,
although the gaseous matter might be expanded, its centre of
gravity would still follow as nearly as possible in the cometary
orbit, not diverge. In other words, from the fact that no
considerable change of orbit is evident after perihelion passage
of a comet, we may conclude that the centre of gravity of
the cometary mass traverses the true orbit of its projection in
space, carrying with it the mass of the tail, and thereby that
it conforms to planetary laws in the same manner as any
other entirely gravitative system of matter.
176. At the time Sir John Herschel suggested that the
tails of comets might be of a kind of matter of which we
have no knowledge, which is antigravitative in relation to
the sun, the spectroscope had not been brought to bear upon
cometary matter. We now know that carbon, hydrogen,
and other elements form constituents ; so that the introduction
of imponderable matter can scarcely be permitted, even hypo-
thetically, in this case. Further, it has never been explained
in this theory, how the cometary matter, after it is expelled
K
130 NOTES ON THE NEBULAR THEORY.
from the sun, recovers its attraction or cohesion, so as to
re-form the actual comet after perihelion as we know from
actual observation that it does. If we adopt the theory of
electrical repulsion as proposed originally by Gibers, and
supported by Bessel, Norton, Zollner, Bredichin, and others,
which is now most popular, this in no way relieves the
difficulty. If the tail is repelled on approach of the comet
to perihelion, with an internal separative force due to
electricity of one sign assumed to exceed gravity, it must
necessarily be left behind, and can never regain the orbit
velocity of the head of the comet. Now this is precisely the
opposite of what is requisite to represent the motion of an
actual comet ; what is required is that the comet shall be
elongated at perihelion, for which the action of gravitation
alone is sufficient, and that the matter of the tail shall have
its velocity of direct projection increased in such a manner
that it shall describe larger arcs at the radii of its separate
parts from the head of the comet, to which the head remains
constantly as a centre during its perihelion passage. It has
been suggested that the tail forms a small part of the
cometary mass and may be re-formed from the matter of the
head : this is in the highest degree improbable, as it is not
necessary that a comet should even possess any head for
that which represents the head is often merely the centre of
inertia of the cometary system which follows in its orbit.
177. Conditions under which a Comet may be considered
as a Planetary Body. Taking the evidence of apparent con-
ditions of comets generally, we find them immense volumes
of what appears to be nebulous matter of somewhat sym-
metrical outward form. Therefore, evidently forming systems
of matter held together by internal forces which must in
some way conform to the laws of gravitation, and so far
resemble planets. We find comets otherwise of very small
density, as is evident from their not disturbing the orbit of a
planet whilst passing near it. Therefore, to account for such
COMETS CONSIDERED AS PLANETARY BODIES. 131
immense volume and small density, in a solitary or planetary-
like system, we have in the first place to consider the
possibilities of ordinary gravitative matter, which we now
know it to be, being held together symmetrically by a system
of forces, wherein the matter itself, although this is in a state
of very great tenuity, remains practically an adhesive system.
178. Now, following the analogy of things known to
account for an enormous diffusion of matter from or about a
central attraction of gravitation, being either engendered or
maintained in an extensive nebula or planetary-like system,
such as a comet may be considered to be ; we have only
three known conditions which may so far react upon a
gravitating or centralizing force in matter to insure this state
of diffusion, tenuity, or decentralization :
1. Heat-forces may separate the parts of a unit system of
matter to any degree of tenuity. 2. Electricity of one sign
may separate attenuated matter similarly to heat but with
greater activity. 3. The tangential action of the revolution of
the outward parts of a gravitative system about a centre or focus
-may separate these parts proportionally to their velocities and
distances from the centre according to the law of orbit to any
degree of tenuity.
If we consider the probabih'ty of the one or other of these
forces being entirely or principally active in a cometary
system, we find, with regard to the first, that to maintain a
degree of heat sufficient to diffuse gravitative matter in a
nebular form to such extreme tenuity as we witness in comets,
we must assume great intensity of this heat, even if we
assume the central attraction small. Further, for this heat
to act as a separative force, we must assume a permanent
gaseous state, as heated solids could not repel one another
to produce the observed volume. Then, again, if we assume
the heat present to be sufficient to account for the extreme
diffusion necessary to produce the known tenuity, still we
have the difficulty present that this heat will be subject to
K2
132 NOTES ON THE NEBULAR THEORY.
constant radiation in space, from all exterior parts of the
system, and therefore the comet be subject to a constant
loss of the decentralizing force, which alone in this case could
support its tenuity. As we know that the larger comets pass
to very distant regions, where little heat can be derived from
the sun, we can scarcely imagine that heat sufficient to
maintain the enormous diffusion of matter we observe can be
sufficiently conserved in their entire systems under the
excessive amount of radiation they must, experience in the
clear cold regions of space. So that we must conceive that
if the cometary state depended upon a force subject to such
radiation, gravitation being constantly active within the
system would, within a moderate period, reduce the comet to
meteoric matter, which, owing to its reduced dimensions as
solid matter, would after a period remain in this state, and
become invisible to us, unless projected very near the earth.
179. Further, if we assume the comet to be entirely
gaseous matter, we can scarcely imagine a degree of internal
heat in the system sufficient to render this, that is the hydro-
carbon portion of it, visible, neither can gaseous matter
reflect the solar rays. Therefore, upon the whole, we are led
to consider the gaseous condition as highly improbable to
account for the observed tenuity, and at the same time the
illumination of the whole comet as a visible body. On the
other hand, it does not appear improbable, with respect to
certain comets, that sufficient heat is maintained in the
nucleus (in some cases, perhaps, from passing very near the
sun) to render this visible in itself, and sufficiently so also to
illuminate the surrounding matter of the comet and tail to
some extent within a certain distance from the sun.
It is not necessary even to consider the nucleus a solid or
liquid body. It may be a rotation-system composed of many
parts reflecting light and yet transparent through the extent
of the interspaces.
180. The conditions under which electricity of one sign,
COMETS CONSIDERED AS PLANETARY BODIES. 133
+ or , could act within a unit system of matter such as a
comet, are difficult to define ; electrical phenomena depend
generally upon the tendency to establish equilibrium, but
with our limited knowledge we cannot say a single form of
electrical energy in a system is quite impossible. If possible,
it may place diffusion of finely divided matter in equilibrium
with the reaction of gravitation for decentralization of matter
in a comet. At the same time, with electricity we stipulate
a form of energy which is exhaustive, particularly if light is
produced, in the same way that heat is exhaustive. So that
we cannot imagine its conservation in the same manner that
momentum is conserved in matter when moving in a friction-
less medium. Therefore, all that we can say is that electricity
probably takes a part in the phenomena of comets, but this
would not account for their symmetrical forms.
As regards illumination of the comet, the probability is
that the electrical action present is a phenomenon exterior to
the general cometary mass, exactly of the kind herein pro-
posed for the illumination of the condensation of pneuma to
nebula, by electrical discharge ( 42).
181. We may now consider the third condition proposed :
That the tangential action of the revolution of the outward parts
of a gravitative system about a centre or focus may separate
these parts proportionally to their velocities to any degree of
tenuity. In this proposition we may observe that, if the
cometary volume is maintained by the revolution of its
outward parts moving in elliptic orbits, we have conditions
that bear a strong analogy to the motions of planetary bodies.
Thus, so far as we know, all planets and systems that we
can observe are in revolution, both in their own masses, and
in the attendant parts of their systems (satellites, rings).
Therefore by analogy, taking the comet to be a part of the
solar system, we must assume that the outward parts of the
cometary system are in revolution. And as the satellite may
revolve at any distance from its primary in an elliptic orbit, so
134 NOTES ON THE NEBULAR THEORY.
also may any of the outward parts of a comet, however small,
revolve. Further, if this motive system is assumed for the
comet, we have the initial energy in the system conserved, as
there is no loss as with heat radiation, unless we imagine
resistance hy a surrounding medium, of which we have no
evidence from other planetary or cometary phenomena.
182. If we admit the conditions first suggested as regards
heat or electricity to be in a certain degree active ; by this
the nucleus of a comet may probably be heated or electrified
liquid or solid matter in unit mass or compounded of many
meteorites surrounded by a gaseous envelope, although this
heat can scarcely be imagined to be sufficient to maintain
the large outward cometary mass of the tenuity observed.
Nevertheless, the nucleus would partly illuminate such
exterior parts as I have suggested are in revolution about it,
but in this we have clearly the necessity that such parts to
be visible should be solid or liquid matter and not gaseous.
Under this condition also the sun would illuminate the entire
system.
In comets that pass very near to the sun it is presumable
that through the great heat the}'- receive near perihelion, any
ordinary matter with which we are acquainted, and which
might form part of the complete comet, would be reduced at
the time to vapour or gas, in some cases possibly by explosion.
This being the case, about perihelion, by radiation of heat
received into space from the gaseous outward parts con-
densations may occur in these parts about separate centres,
again developing heat and electricity. The units of conden-
sation may form sphericles under the same conditions as
clouds are formed in the earth system. These would appear
in mass as cloud, and in this state would traverse the orbit
of the cometary system, forming parts of the coma and tail.
If the head of the comet was in rotation, the condensed units
would be in revolution at any extended position therefrom.
Now, as regards the magnitude of each solid separate part
COMETS CONSIDERED AS PLANETARY BODIES. 135
or particle now suggested as an outward revolving part of
the cometary system, this may be as small as we like to
conceive it, assuming its mass sufficient to reflect a ray of
white light. For the existence of such minute cometary
matter, we may possibly find some analogy in the system of
small meteors which revolve in elliptic orbits about the solar
focus, and which are sometimes brought within the attractive
distance of the earth, evidence of which is further given by the
cosmic dust discovered in snow by Prof. Nordenskiold *.
183. A form of particle which may be probable as a result
of uniform condensations is that of a smooth bright metallic
or vitreous sphere, which is covered with a permanent gaseous
condensation, of hydrogen or a light hydrocarbon, which,
under the sun's influence, may produce a gaseous envelope in
the same manner as the earth is surrounded by its atmosphere.
The refraction of the gas intensifies the sun's heat and light
upon it. Refraction and reflection will carry over part of the
light to other such globes at greater distance from the sun.
Further, when the comet is sufficiently near the sun for its
heat to render the gas, if hydrocarbon, incandescent in the
purely isolated state, the comet may possibly become self-
luminous.
The change of state from the solid or liquid to the gaseous
will also develop electrical conditions which may render its
matter temporarily luminous when approaching the sun or
receding from it by the effect of after-condensation.
184. If the exterior cometary matter in separate particles,
as proposed, is in rapid revolution in very elongated elliptical
orbit round the nucleus of the comet, which I assume is
necessary to maintain the extent of what we may term the
cometary volume of the tenuity observed, then this revolving
matter may be projected in elliptic orbits, either as separate
particles (satellites), or more probably in accumulations or
* Voyage of the 'Vega V
136 NOTES ON THE NEBULAR THEORY.
series in one or more connected gravitative systems in the
form of more or less perfect rings or bands, the orbits of
which, about the head of the comet, may cut the solar-
cometary plane at all angles. I will now endeavour to trace
diagrammatically what would be the action of such a system
whilst moving in an elliptic orbit round the sun.
185. Comet-tails. Trains. Under the gravitative con-
ditions proposed, the word tail will be entirely a misnomer,
as the matter which forms the tail of the exterior parts in
revolution about the nucleus is assumed to change position
and become at another time part of the head. I will call the
revolving parts of the head the pericoma, and the extreme
of the tail the apocoma. For the entire comet except the
nucleus, I will use the word train, which has been sometimes
employed before.
186. Following the conditions proposed, that the comet is
made up of separate parts moving closely together in rapid
revolution around the nucleus, we must then assume, by the
laws of gravitation, that the centre of gravity of the mass
held by mutual attractions will be constrained to follow an
elliptic path for its orbit. But the separate parts of the
system which together form the train may describe elliptic
curves about their common centre of gravity, that is the nucleus,
modified by their mutual attractions to each other , in combination
with the attraction of the sun. This may be taken in detail.
187. Elongation of the entire Cometary Mass near Peri-
helion. Now, as regards the proper motion of the system of
the comet constituted as suggested, we may consider that the
velocities of its separate outward parts, as of all planetary
systems including satellites, are such that the areas described
by the radii vectores are proportional to the times that is,
in relation to their own focus, and so far as this system is
undisturbed by other attractions. Further, we know nothing
in astronomy of resistance by a surrounding medium ; there-
fore, however small we assume the exterior separate parts
ELONGATION OF COMETARY MASS NEAR PERIHELION. 137
which are linked together by mutual attractions to form the
train of the comet, these will separately maintain their
velocities in relation to the nucleus consistently with the
length of curves described by their radii vectores in equal
times.
188. These premises being granted, we may next consider
the conditions present of the relative attractions upon the
separate parts of a cometary mass in combination with that
of its superior focus the sun. For this we may first, to save
the complication of superimposed motions, consider the comet
upon the Swarm theory as an immense system of matter in
separate parts, either as a number of separate meteorites or
cosmic or nebulous matter, connected closely together by
mutual attractions but forming an elastic system. The
matter exterior to the nucleus is assumed for the present not
to be in revolution about the nucleus, as our theory demands
that it should be. Then suppose that the whole matter of
the comet is moving in its orbit. Take this diffused mass at
the position of aphelion, at such a distance from the sun
that the sun's attraction would not materially disturb the
arrangement of its parts. It will then be clear that as the
large cometary mass (now assumed not in revolution)
approaches the sun, each of the separate parts of the mass
will be accelerated directly as the length of curve described
by its radius vector in unit of time about the solar focus.
Therefore, the forward parts traversing space towards the
sun will move at this approach much more quickly than the
following parts, and the entire comet, possibly globular at
aphelion, will be enormously elongated into ellipsoidal form in
passing very near the sun. By the same laws also acting
inversely in passing from the sun, its mass will be contracted.
This principle is shown by fig. 16.
Let S be the sun, and a b c three particles of matter in
the train of the comet which is revolving in an orbit around
the sun shown by the surrounding line. Let a be a forward
138 NOTES ON THE NEBULAR THEORY.
particle, b a central particle, and c a following particle.
Then will the velocity of a be greater than that of b at the
period of approach towards the nucleus, and b greater than c
proportionally to the lengths of curve described by their radii
Fig. 16.
vectores in unit of time ; so that as the comet approaches
the sun its mass system or volume will be elongated in
space in proportion to the excess of attraction to its forward
parts by acceleration of gravity over its following parts. And
under these conditions the greater the eccentricity of the
orbit, that is the greater the acceleration at perihelion, the
greater the length of the train of the comet. So that the
outward form of the comet would in degree, so far as present
conditions are considered, resemble its own orbit in form.
189. Under the above conditions, we may observe that,
upon the whole, in considering the cometary mass as not
being in revolution, all the parts in any plane would follow
each other in elliptic orbits about the sun ; and although the
tail or following part would constantly increase in length in
approaching the sun, it would not diverge from the sun in
passing near it, or the separate parts move out of their separate
solar orbits as gravitation units. Therefore there must be
present, as generally admitted, other conditions to account
for the divergence which is universally observed. In this
proposition it is assumed that it is possible for the outer parts
of the comet at greater distance from the sun to possess
the same orbital velocity as the inner parts moving nearer
ORBITS OF OUTWARD PARTS OF A COMET. 139
to it, so that the figure of the comet may be conserved, as
erroneously assumed by others in the discussion of the Swarm
theory, in opposition to Kepler's third law.
190. Orbits of the outward parts of a Comet. Focal
Point. We may now follow the conditions just proposed,
and assume that the comet resembles a planet surrounded by
a connected revolving system of matter equivalent to a system
of satellites, or to Saturn's rings, this revolving matter being
meteorites, dust, or nebulous matter, and that the revolving
mass (which I have denominated the train) will not only be
sensitive to the attractions of its own parts and its nucleus or
the centre of inertia of the system, but also to the attraction of
the sun at the same time. Then, as the sun's attraction will
not be linear with the major axis of tJie comet's mass in its
assumed elongated form, the outward parts of the train,
which are projected forward of the nucleus during their
rotation, will be accelerated and be drawn towards the sun,
and if the motive direction of these is inwards towards the
sun, as it will be in the exterior part in revolution in the
solar- com etary plane about the nucleus, these will be drawn
towards the nucleus also; and in the smaller arc thereby
induced by increased attraction will have their velocity
accelerated (Kepler's second law) . In this manner, although
the matter of the train will be elongated in space by the
differences of velocity of its parts in passing over separate
portions of the curve described by its radii vectores ; still the
nucleus of the system will maintain a position at the forward
focus of the orbit of the train, and parts of the train will be
induced to move in an orbit round its nucleus, or the centre
of gravity of the system, which will closely resemble that
of the superior orbit of the entire comet in moving round
the sun.
This matter may be better conceived by reference to the
diagram fig. 17. Let S be the sun, C the nucleus of the
comet, a a particle moving in its orbit in the solar-cometary
140 NOTES ON THE NEBULAR THEORY.
plane, shown by an elliptical outline. Draw a line through
the centre of the sun, and through the nucleus of the comet
to represent the linear direction of gravity on the orbit
Fig. 17.
shown by the outline. Then will the combined attractions
of the sun and the nucleus exert greater attraction upon a
particle in this position a as the comet approaches nearer
the sun, than was exerted upon it at the same position of
the orbit by the nucleus only, and such attraction will cause
the particle to move faster and nearer to the nucleus, or
inwards in a direction from a towards the point a'. In such
a position its forward radii vectores in relation to the comet's
centre of inertia will be closed, and its velocity increased
proportionately to the lengths of curve now described by its
smaller radii vectores. It will thus also maintain the nucleus
at its focal point within the comet, although the cometary
mass be elongated by the increased velocity of its forward
parts at pericoma as shown above.
191. Direction of the Cometary Train in Relation to the
Sun. By the above conditions it will be seen that the
separate particles of the train of the comet will be actuated
by forces which will be the resultants of the combined
attractions of the sun and those of their own proper nucleus,
the pericoma of the train, if this principle is admitted, moving
DIRECTION OF COMETARY TRAIN IN RELATION TO SUN. 141
about its head will come constantly in the direct line of
attraction between the sun and the head, and will constantly
change the direction of the attractions upon the parts of the
train. The particles of the train will also be subject to the
attractions of their own masses upon one another ; and if
the train is a combination of dust or meteorite ring-systems
as suggested, these attractions will still further modify the
conditions given. The principle now offered may be best
described diagrammatically by fig. 18, for which I will again
take the position of revolving matter on the solar-come tary
plane only.
192. Thus : Let S be the sun, C, C', C", fig. 18, three
positions of the nucleus of a comet moving in the orbits
Y Z, Y' 71, and Y" Z". Let d e be two particles of matter
which form part of a continuous attractive series constituting
the train. When the nucleus is at C, and moving in the
Fig. 18.
orbit Y Z, then will the continuous series of particles arriving
at d be not only actuated by the attraction of their nucleus,
but will be accelerated by the attraction of the sun directly
linear to their motive path in the direction d, as before shown
a to a! in fig. 17, and all following parts as they arrive will
142 NOTES ON THE NEBULAR THEORY.
be mutually attracted in series in the same direction. There-
fore the particle d, fig. 18, will be both accelerated, and be
drawn at the same time towards its nucleus C, and by the
curve of its smaller radius vector it will pass nearer the nucleus
with greatly accelerated speed.
193. Now, as regards the attraction of its nucleus and the
velocity engendered in particles moving about it by the
attraction, the velocity would be maintained, varying only
in inverse proportion to the squares of length of its radii
vectores onwards to e ; but from d to e the sun's attraction
would still draw the particles towards the cometary nucleus,
so that throughout perihelion passage the curvature would
be in a certain degree maintained as at perihelion, directing
the particles of the train thereby towards the point x. The
apparent effects of this will be that the whole mass of the
train considered as an elliptic mass in revolution will be, as
it were, pulled forward in the direction of its rotation, and
whirled round in space so that the position of the suns centre
may be maintained constantly linear with the least radius
vector of the parts of the train that pass nearest to it, and
the whole train of the comet, although describing an ellipso-
epicycloidal curve, will be as far as possible constantly
symmetrical about the nucleus ; the orbit of the train thereby
changing to make this possible from the positions Z Y to
Z / Y ; , Y" 71' when the nucleus of the comet arrives at positions
C, C', and C".
Under the above-stated conditions the revolving matter
of a comet passing its perihelion will possess much greater
absolute velocity than the centre of gravity of the comet.
Therefore a comet may pass very near the sun's surface with
momentum too great from this self-rotatory velocity for its
matter to be materially disturbed by slight resistance of
attenuated matter, if such exists about the sun.
194. Widening and Curvature of the Train by crossing
Orbits. One other point to be considered under the conditions
WIDENING OF THE TRAIN BY CROSSING ORBITS. 143
given above is that the newly placed pericoma at every
change of position in relation to the cometary nucleus, as it
becomes directed towards the sun, will influence the parts of
the train only in proportion as they are accelerated. There-
fore, the parts of the nucleus which have just passed the
pericoma will have the accelerative force due to the sun fully
impressed upon them, whereas the parts arriving there will
not be so fully impressed, but will retain a part of the force
due to their initial velocity in relation to the previous position
to the nucleus at the last time they passed between it and
the sun. Therefore, the following parts will not maintain
quite a symmetrical position with respect to their future
pericoma, but will lag behind this position, so that the general
path of projection of the train will be constantly of greater
curvature upon the exterior of the orbit than in the parts
nearer to the sun.
195. If the matter in revolution about the cometary nucleus
revolve in different periods according to Kepler's third law,
as the planetary matter about the sun does, then the orbits
Fig. 19.
of the parts of least period of revolution, which will be nearer
to the nucleus, will appear to lag less than the outward
parts of longer revolution period about the nucleus, so that
144 NOTES ON THE NEBULAR THEORY.
by this means a crossing of orbit will occur, producing either
a widening or opening of the tail. Under these conditions
also possible collisions may occur, producing complicated
effects impossible to follow here. Fig. 19 represents the
normal conditions in the solar-cometary plane where the
crossing orbits are assumed to be conserved.
196. Let S be the sun, C thecometary nucleus, ^represent
the orbit of a particle of early revolution, e the orbit of a
particle of later period. After perihelion of the entire comet
in relation to the sun, this system of forces, by the changed
dispositions of attractions, will act inversely.
197. Formation of a neiv Head or PericepJialion about
Perihelion Passage of the Comet. Under the above conditions,
independently of the complication of motion of cometary
matter moving in orbits not in the solar-cometary plane, the
conditions of which have not been separately considered,
incidental phenomena must occur which will, more or less,
disturb the general conditions thus : As the sun causes
acceleration to the parts of the train in approximating their
pericoma in relation to the head, and retardation to these
parts in leaving it, the matter of the train will be more con-
densed round the head in the point of pericoma of the system,
and thus form incipiently a new head, which will react, by its
gravity, as a secondary or false focus, and in its turn, by
maintaining the centre of gravity in the cometary orbit, will
tend to disturb the position of original matter that formed
the original focus. At the same time, if the comet passes
very near the sun, the head, by the great heat it receives,
will be expanded or even exploded ; so that it may become a
less dense mass ; or even new heads may be again formed
forward of this with a general relative disturbance of the
internal gravitation in the parts of the cometary system, the
conditions of which are too difficult to follow.
198. It is at this point where, as pericomic matter increases
in density at the head of the comet, and heat forces, and
SOME GENERAL CONDITIONS. 145
possible development of electricity, cause great increase of
internal elasticity, the orbits of train-matter may be separated
by explosion, so that a comet may be divided into two or
have a large part of its train detached from its own focus,
one part to be retarded in its orbit as much as the remaining
part of the comet will be accelerated mass for mass. Or the
complexity of orbital conditions induced may separate a part
of the train about perihelion where solar action is most
intense.
199. Some General Conditions. As to certain appearances
of comets under the conditions proposed, which will influence
the spectra obtained therefrom if the nucleus of a comet is
a heated or electrically excited mass, which it may become
by the collisions of parts of the train in revolution near
pericoma, or by heat derived from the sun. Under the same
conditions the train in passing pericoma may be also heated
or electrically excited sufficiently to become luminous or
phosphorescent. This luminosity will gradually die off in
the distance, so that possibly the parts of the train of a comet
in aphelion are seldom visible. From which we may con-
clude under these conditions that visible comets are generally
only the parts of the cometary system that are nearest the
nucleus. In the comet of 1882 (Wells) I was anxious to
observe whether any appearance could be detected of orbital
projection beyond the extent of visible tail, which could be
possibly observed by some obscuration of part of the faint
light from celestial space circumscribing a curved elliptical
space. This partial obscuration I fancied I observed on the
23rd October at 5 A.M, It was also observed as a darker
part behind the visible tail by Mr. C. J. B. Willians at Cannes,
France*, as also by Mr. Henry Cecil at Bournemouth f.
200. Upon principles here discussed the cometic matter
in revolution about the nucleus causes each particle to be
* Nature, Oct. 26, 1882, p. 662. t Nature, Nov. 16, 1882, p. 52.
L
146 NOTES ON THE NEBULAR THEORY.
illuminated by the heat or electrical excitation engendered
through constant collisions, also by the heat of the nucleus,
and by that of the sun on the side turned towards it. There-
fore the light we receive by reflection will be proportional to
the amount of illuminated surface of the revolving particles
visible to us, and the direct light that of incandescence. In
this manner the nucleus itself may become invisible or dimmed
by eclipse of revolving incandescent matter about it. On
the other hand, the light received directly from the nucleus
will be proportional to the open spaces only between the
outer revolving parts crossing the field of light. From these
causes it is possible that some of the most remarkable appear-
ances of projection of cometary matter suddenly from the
nucleus through immense distances may be merely the
lighting of the distant parts of the train of cometary matter
through interspaces of the central system upon dispersed
matter which, although present, was previously invisible
to us.
201. The matter of some comets, of which Encke's is
perhaps one, may be a carbon-hydrogen compound, which in
the distance of space, as at aphelion, may be condensed to
particles of solid matter, but in nearing perihelion may be
again converted into gas by the heat of the sun with develop-
ment of incandescence through electric excitation sufficient
to render it visible. This matter may again condense in
passing towards aphelion, the orbit position of the separate
units of the system remaining the same with the electrical
effects of change of state the apparent outward visible
volume of the comet varying according to the conditions
observed.
[ 147 ]
CHAPTER X.
THE EARTH. CONSIDERED IN EVIDENCE OF FORMER NEBULAR
CONDITIONS. ITS INTERNAL FLUIDITY. TIDAL FRIC-
TION. CHANGE OF FIGURE DUE TO ROTATION.
202. The Earth may be considered as a model planet
whereon we are able to observe the evidences of exterior
conditions which are due to phenomena that have acted upon
it to produce its present form and constitution. In this study
we may possibly approach the conditions which also ruled
in the formation of all the dense planets interior to Jupiter,
of which we can possibly obtain no further evidence of struc-
ture than that apparent upon the surface of Mars and the
moon.
203. To assure our premisses for earth-structure it will be
convenient briefly to recapitulate some general propositions
that have been already discussed, which we may possibly
accept as data for certain factors of early formation. The
most important of these are : 1. That the solar-planetary
system during condensation possessed more or less nebular
matter projected about its equatorial zone, as represented
diagrammatically by the discoid form in fig. 9, p. 67. 2. That
the tenuity of the planet-forming system interior to Mars
upon the condensation of the sun's volume, was too great to
support the nebulous concrete state at a period when the
exterior solar nebula was falling below its critical temperature
( 112). So that within the orbit of Mars local separate con-
densations were formed at first of the more refractory matters
L2
148 NOTES ON THE NEBULAR THEORY.
widely exterior to the earth's orbit. 3. That at the early
period when the intra-Mars local condensations were forming
the earth's nebula was still attached to the sun ( 146) . 4. That
the exterior local condensations of matter at an early period
were drifting sunward into the earth's nebula and towards its
orbit position in moving under the resistance of the surround-
ing less refractory nebulous matter. So that the earth during
its formation at no time extended in an entirely uncondensed
nebular form so far as the orbit of Mars. 5. That the
earth's formation being partly but not entirely due to the
condensation of gaseous matter as assumed herein of the
planets Jupiter and Saturn a denser system was produced.
204. Under the above-stated conditions we have the
suggestion of two large factors of earth - formation : An
interior nebular system about the earth's orbit of purely
gaseous elements, which were sinking at the period of forma-
tion to a critical point of temperature and impressing their
virtual momentum upon the earth in the direction of its
rotation, upon principles already discussed 128, and an
exterior condensation system of meteorites or planetoids which
were projected into the earth's nebula. These, as bodies
moving in nearly free orbits, that is, under slight resistance
of the residual nebulous matter, drifted into the earth's nebula
in spiral orbits that upon contact with the then forming earth
may have produced effects which continue to be evident
upon its surface.
It is necessary in this matter to insist upon the con-
tinuance of nebular conditions during the greater part of the
period of the formation of the mass of the earth, as such con-
ditions alone could have produced its present direction of
rotation, as it was shown originally by Descartes and Laplace
( 7), and with equal clearness by M. Faye ( 141), that if
it were formed from an entirely discrete system of matter
moving in free orbits its direction of rotation would be the
reverse of what it is.
FORMER CONDITION OF THE EARTH. 149
If we oinit from consideration the projection of discrete
matter into the earth's nebula, which would carry with it
certain elements of relatively retrograde momentum accord-
ing to the theorem of M. Faye, the necessary extent of nebula,
if this alone was active, may be inferred by taking the
formula 27T7' 2 D = 2 TT(I\ r), from which we find T)r 2 + r=r ly
D being the days in a year, r 2 the radius of the earth, r the
radius of the earth's orbit, r t the outer radius of the nebular
ring, which by calculation to produce the present rotation is
found to be of about 1,000,000 miles greater radius than the
earth's orbit.
205. If while the earth was moving at nearly orbital
velocity there were projected upon it certain factors of discrete
condensation, giving a momentum the reverse of that due to
direct condensation of gaseous matter, the radius of the
original gaseous matter would have to be increased in pro-
portion to the momentum of the discrete matter in order to
account for the present rotation period.
If we accept the conditions proposed above, they entail
certain relative consequences of which we should expect to
find evidences in earth-structure.
206. Firstly : If the earth were condensed from a gaseous
system, this condensation could not have been effected without
producing an intense heat in the condensed matter, as it may
be supposed to have resembled our sun in constitution at an
early period. Further, such heat as would be produced by
gaseous condensation must have also rendered any discrete
matter which may have been projected therein liquid.
In the formation of oxides upon the earth, if these were
produced from elementary matter, the only probable condi-
tion, they must also have produced great heat during their
oxidation. At the same time, as such oxides are lighter than
their metallic bases and are non-conductors of heat, they
must have rested upon and covered the surface and conserved
the central heat. Therefore we demand, ' in the first place^
150 NOTES ON THE NEBULAR THEORY.
upon these conditions, evidences of a highly-heated liquid
interior.
207. Secondly : If the planetoids, large or small, produced
by the condensation of matter exterior to the earth's nebula were
incorporated therewith when the earth became a liquid planet,
then such matter within or upon the earth's surface might pos-
sibly remain geologically evident. Particularly such planetoids
as may have drifted to the earth's surface when all the denser
matters of its nebula were condensed. Under these conditions
it remains probable that some land-areas of the earth may
show evidences of this discrete form of condensation. These
conditions are so far actual that we have still planetoids, that
is, meteoric matter, falling to the earth.
208. The nebular conditions which upon the theory herein
proposed would have been constantly active at an early
period of earth-formation require consideration in detail.
They will therefore be deferred to another chapter with the
exception of the argument upon which they must be supported
of the entire internal fluidity of the earth. This also is
necessary for the consideration of the effects of later discrete
projections upon the earth to be discussed in the following
chapter, as I suggest that these discrete projections were
coincident with nebular condensation and may remain, at
present, evident in land-formation.
209. The Internal Fluidity of the Earth. This could not be
questioned for a moment if the evidences of observation were
alone considered, but in the contemporary science of any
period we have generally in popular learning a tendency to
depart from concrete observations directed to consider some
hypothesis or isolated fact, which is elevated to predominance
above all the natural conclusions of otherwise universal
observations. I remember, when a cool sun was the prevail-
ing theory, arguing with a professor that the intense heat of
that body was manifest in many ways. His reply was that
that was nothing to the purpose if the solar spots were found
THE INTERNAL FLUIDITY OF THE EARTH. 151
to be hollow places or cavities in the sun's surface ; as they
were dark they must be cool ; and science must take account
of every phenomenon. If experience teaches us anything, it
is that theories change with every phase of science ; so that
our safety, if we are seeking truth, lies in taking the mean
evidence of all relative phenomena, not of any single pheno-
menon which we may or may not perfectly comprehend.
The most important evidence of the former nebular
condition of the earth besides its direction of rotation is to
be found in its interior condition ; for it is certain, as just
stated, that the matter which forms the earth, if it pre-
viously existed in a gaseous or vapourous state, must have
been condensed from this state to a liquid with great
development of heat. The density of the system also clearly
indicates that the internal matter, if at a high temperature,
is most probably metallic. Now as it is the property of
metals to alloy and also to conduct heat, it is in the highest
degree improbable, as sometimes supposed, that any part of a
uniform system of condensation, as that of the earth, could
be for ages intensely heated in some interior parts, and cool
or solid in other parts. It therefore becomes a rational con-
dition of the nebular hypothesis that the interior of the earth
was, or is, in a highly heated uniformly liquid condition.
210. If the earth at an early period condensed refractory
metallic matter to form an intensely heated globe, while this
was surrounded by less refractory matter, and particularly by
oxygen, near the surface, then the globe would be formed
mainly of the refractory matter, and be covered with the
oxidized matter upon its further condensation. The oxidized
matter must necessarily have rested upon and outwardly
covered the metallic matter, so that possibly at a very early
stage of condensation there was a metallic uniformly heated
globe covered with a coating of non-conducting oxidized
matter as we find it at present, although this coating at an
early period would be very much thinner than it is now.
152 . NOTES ON THE NEBULAE THEORY.
As the earth cooled the coating must have increased by
condensation and protected the earth more and more from
radiation of internal heat until it was possible for water to
rest upon the earth ; so that the heat of the interior must have
been protected by non-conducting material, highly heated
from chemical combination, in such a manner that it could
only very slowly radiate its heat into space.
211. We now arrive at an important point. Is the inte-
rior of the earth fluid ? From mathematical physics alone
in the accepted theory of the tides, Lord Kelvin, our greatest
authority, says that it is solid, or the tides would not present
the great variation of height of surface which we witness. This
matter is repeated with authority in the recent compilations
of Lord Kelvin's works *. There is one point of this theory
at least which astronomers ought to be able to solve. Lord
Kelvin shows that the necessary result of tidal friction is
that the earth's rotation must be decreased by a total value
of twenty-two seconds in a century ; and the establishment of
this as a fact might tend to prove the certainty of the effects
of tidal friction upon the earth, and at the same time possibly,
if we had no other direct observations to consider, of the earth's
solidity. If we depart from physical theory and follow the
evidences of astronomy by observation, wherein the data are
results of experience not liable to receive much correction
from change of theory, we have undoubted authority from
observation that the rotation period of the earth, considering
the moon and Mercury particularly as time-keepers, has not
decreased by a single second in a thousand years.
212. If we follow the evidences of geology founded upon
observation, the solidity of the interior of the earth appears
to be quite impossible unless we assume an unknown form of
matter which does not become fluid at a high temperature.
We need only cite a few instances to show the improbability
* Prof. 0. J. Lodge. Keview in < Nature,' July 26, 1894.
THE INTERNAL FLUIDITY OF THE EARTH. 153
of the rigid solid earth proposed by Lord Kelvin. In
every considerable volcanic eruption, even within modern
times, the matter that issues from the earth is at a white heat;
and although this may be reduced to dust, as in the Krakatoa
eruption, the microscopic examination of the dust shows
clearly by structure that it was formerly, or just before its
issue, at this heat and in a liquid state *. We find also that
this matter may again be reduced to liquid at a heat much
Jess than that at which it was thrown from the volcano. The
mass of matter projected from Krakatoa is estimated to be
equal to about 22 solid miles. The eruptions of other moun-
tains in Java were of much greater mass. The liquid lava
that issued from Skaptar Jokull in Iceland, in 1783, is
estimated at 21 cubic miles. The lava of the Snake river,
Idaho, North America, that has issued in tertiary times is not
of much less volume than 500,000 cubic miles. We have
also upon the surface many thousand cubic miles of lava in
Abyssinia and in other parts that has certainly issued at a
white heat. Further, the axes of our mountain chains are
built up of plutonic matter the structure of which shows the
evidence of former intense heat with extrusion of liquid
mineral matter. This is evident although the surface-matter
is often dislocated and rearranged so as even to include
superficial sedimentary rocks, the deep-seated felsitic rocks
seldom intruding beyond the base of a volcanic chimney.
The volcanic and sub-volcanic matter, therefore, upon the
earth's surface, which has evidently been in a liquid state,
amounts to many millions of cubic miles. When we consider
the wide distribution of this matter, its nearly uniform mineral
structure, and its present almost constant issue, as in Kilauea
and other volcanoes, we cannot but conclude that it formed,
and now forms, a part of a general system whose intense heat
* See author's paper, ' ' Krakatoa Dust/' R. Met. Soc. Quart. Journ.
vol. x. p. 187 (1884).
154 NOTES ON THE NEBULAR THEORY.
is derived from the uniformly heated state of the central
matter of the globe.
213. The evidence of the thermometer, which shows that
there is a general increase of temperature with depth of ahout
1 Fahr. for every 60 feet, where freedom from the influence
of percolated water permits this measurement to be made,
gives an increase of temperature of 88 per mile ; so that at
about 200 miles we should have, at this rate, a temperature
of 17,600, which no known body could bear while retaining
a rigid state. It is not, however, necessary to consider a
constant increase of heat if the central volume is metallic, as
herein proposed, for a good heat conductor would distribute
heat equally in the interior. The following suggestions may
be offered as regards the internal liquidity of the earth.
Fig. 20.
214. Is the assumption of the solidity of the earth neces-
sary to account for tidal action ? Having devoted some years
to the consideration of motion in fluids, I find that the mobility
of liquids depends greatly upon the freedom of surface, which
adapts it to offer certain forms of accommodation for motion
THE INTERNAL FLUIDITY OF THE EARTH. 155
for which time is required. So that a dense liquid held in
equilibrium by surrounding pressures, such as we may
imagine the interior of the earth to be, offers considerable
resistance to deformation through molecular friction in
moving from a state of relative rest until certain forms of
accommodation can be brought about, which are nearly im-
possible in a close system. In firing an Enfield rifle bullet
directly upon the surface of water, the point of the bullet does
not pierce the water, but the water pierces the bullet, and
reduces it to a thin conical shell *. Fig. 20 shows a full-
size section of the bullet. Fig. 21 was taken directly from
this bullet fired from an Enfield rifle normal to the surface of
water through a thin piece of bladder in the end of a deep tank.
The point of the bullet was painted red, and left to dry.
The colour upon the point was found spread out to the ex-
treme circumference, where it formed a curled-up edge, as
shown in the figure, a a a. The centre of the figure shows
the pressed out diaphragm of the bullet, which was reflected
from the surface of the water, so that it forms no part of the
scheme.
The velocity of the earth's surface at its equator is much
greater than that of the bullet; therefore we have to consider
accommodation in the waters of the ocean and of the liquid
interior for displacement in relation to time, in order that it
may possess a certain form of possible motion of accommoda-
tion. This presents a difficult problem, the factors of which
are, for the greater part, quite unknown. If, on the other
hand, the deformation under the moon's attraction is considered
to depend upon the elasticity of the system, then a solid is quite
as elastic as a dense liquid under great compression, so that
neither solidity nor liquidity could be inferred from this
cause. Gold or steel in a solid state is much more yielding
under pressure in confined space than water, as is proved in
* 'Fluids,' p. 187.
156 NOTES ON THE NEBULAR THEORY.
the coining of metals, in contradistinction to the compression
of water in the hydraulic press.
215. Judging from the constitution of meteoric matter
that has fallen upon the earth, assuming cosmic matter in a
certain degree general, the centre of the globe would be
largely composed of nickeliferous iron. As regards this
matter, we have not been able to produce any temperature in
our furnaces high enough to melt it, so that assuming this
formed the larger part of the interior of the earth upon which
the surface rocks rest, the white heat of volcanic matter as it
issues from the surface of the earth, taken as an index of the
interior temperature, would only be sufficient to raise pure
iron or nickeliferous iron to a stiff' plastic state, as iron in
forging offers very great resistance to change of form under
great surrounding pressure.
216. It is certain that the earth's rotation upon its axis is
combined with that of the rotation about the centre of inertia
of the earth and moon ; therefore there must be a swing in
the free surface of the ocean, due to its plus and minus daily
and monthly rotation-velocity in relation to its position with
respect to the moon, which must produce tidal action in the
free surface water. But how far this plus momentum in one
part is compensated by the minus momentum in another may
be a difficult problem to solve. One must, however, feel in
this, as in other instances with which history furnishes us, that
in the intent observations and calculations of certain actions
we are liable to lose sight of the reactions that are not super-
ficially evident or may be unknown. So that it becomes a
question whether the motions within and about the earth
moving in its orbit in frictionless space seriously affect its
general momentum of rotation taken in a wide astronomical
sense, so that we may infer its internal condition therefrom.
Certainly, taking the matter in its entirety, we cannot suppose
it to deviate greatly from Newton's Third Law, Cor. iv.: " The
common centre of gravity of two or more bodies does not
EFFECTS OF TIDAL FRICTION. 157
alter its state of motion or rest by the actions of the bodies
among themselves."
217. Effects of Tidal Friction. Taking account of the
suggestions offered in 153 for comparing the revolution of
the moon with the rotation of the earth upon nebular con-
ditions, the effect of tidal friction upon the present rotation
of the earth must have been very small, the proof of
which is quite evident in early geological stratification. That
there have been certain effects is suggested to be made evident
by the present acceleration of the moon of 10" or 11" in a
century. This effect was suggested by Kant and afterwards
worked out mathematically with varying results by many
eminent astronomers. Laplace accounted for the acceleration
by decrease of ellipticity of orbit. These calculations being
revised by our late eminent astronomer and mathematician
Adams with greater precision, reduced the Laplace factor by
6", leaving a residual 4" or 5" to be accounted for by tidal
friction or some other cause *. Whether this residue may be a
recurring differential from astronomical causes remains to be
proved. If we take it to be a constant of acceleration due to
tidal friction, then subtracting the Laplace-Adams factor,
and assuming the earth's angular rotation-velocity to have
been retarded in the same ratio as the moon's angular revo-
lution-velocity was accelerated, and considering 5" per century
as the mean acceleration, we have a period of about 12 millions
of years for the time that the angular velocities of the earth
and moon were equal ; that is, the condition assumed herein
of the purely nebular state before the separation of the earth
and moon, which must have been followed by a long period
of time before there could have been any geological conditions
that could remain evident in the structure of surface rocks.
This short period can, therefore, scarcely be discussed if we
take any recognition whatever of geological evidences.
* Phil. Trans, vol. cxliii. p. 397.
158 NOTES ON THE NEBULAE THEORY.
218. Change of Figure of the Earth due to Rotation-velocity.
If there are sufficient scientific data to assume that our pre-
sent day is longer than formerly, of which there appears to
be a probability only within very narrow limits, then this, so
far as concerns the present investigation, points to the con-
clusion that the mean symmetrical figure of the early earth
as a spheroid of revolution must have been changed by this
condition and have been at the time of greater rotation-
velocity more oblate. Upon the nebular condition just dis-
cussed, the difference could not have been great. The effects
of contraction of the equator under decrease of velocity, if
we may take it at the extreme value accepted by some
scientists, was ably discussed in a paper read by Mr. Wm.
B. Taylor * before the Philosophical Society of Washington,
May 3, 1885.
219. Mr. Taylor takes the very extreme condition proposed
by Prof. G. H. Darwin of a rotation period of six hours, which
must have produced an elevation of land at the equator one-
tenth greater than at present, assuming the earth to have been
a true spheroid of revolution. He finds that this would make
the equatorial radius 4359 miles and the polar radius 3291
miles only. The pole would be therefore 658 miles nearer the
centre and the equatorial protuberance 396 miles higher than at
present. Mr. Taylor suggests that this would account for all
the crumpling and inclination of strata and the elevation of
mountain-chains. It is very doubtful whether it would do
so ; the mean inclination of strata at all depths is probably
not less than 20, and this could not be produced even with
one tenth the equatorial contraction, supposing the inclina-
tion in the past constantly increased instead of oscillating
locally up and down during all geological time, which must
have been the case from local volcanic disturbance that is quite
evident in extreme cases by some strata being quite over-
* American Journal of Science, 3rd series, vol. xxx. p. 249.
CHANGE OF FIGURE OF THE EARTH, 159
thrown and inverted. Nevertheless it may be much more a
vera causa than the contraction-theory of the late Robert
Mallet. It may have been a cause of elevation of land in
the tropics as an early condition, but it must have been
materially modified by the condensation of nebular matter
at the poles which I shall propose further on.
220. The effects of the rate of rotation of the earth upon
its oblateness appear to have been first suggested by the
Rev. 0. Fisher, and carefully considered; but he regards them
as very slight. In his interesting work on the ' Physics
of the Earth's Crust ' he says : " The friction of the tides,
whether oceanic or bodily, must necessarily have diminished
the rotational velocity and lessened the oblateness. The parts
of the crust about the poles will have been subjected to
stretching and those of the equator to compression. There is,
however, no apparent reason immediately to connect the
inequalities with this cause, for the continents do not occupy
an equatorial belt, as they would do under this hypothesis,
nor have the polar regions been free from the compression
which all continental areas have experienced " *. This fact
appears to me to be a sound objection to the whole hypothesis
of a former rapid rotation of the earth, seeing that the known
geological evidences of early stratification are directly opposed
to it.
* ' Physics of the Earth's Crust,' Chap. xiv. p. 183.
[ 160 ]
CHAPTER XI.
SUGGESTED SUPERFICIAL CONDITIONS OF THE FORMATION OF
THE EARTH, PARTICULARLY THOSE DUE TO DISCRETE
CONDENSATIONS WHICH MAY HAVE BEEN FORMED PRINCI-
PALLY BETWEEN THE EARTH* S ORIGINAL NEBULA-ZONE
AND THE ORBIT OF THE PLANET MARS.
221. Formation of Land-areas by inclusion of Planetoids
into the Eartlis Surface. In this chapter it will be convenient,
in order to simplify the subject, to take the conditions which
were proposed secondly ( 207) of the factor of earth-formation
from planetoid matter, deferring the more important con-
sideration of nebular formation until the next chapter. The
fall of meteoric or planetoid matter which may have been
formed originally by condensation in a part of the space-
interval between the earth's original nebula-zone and Mars
will be now considered.
222. Assuming the discoidal system of our sun's nebula
shown in fig. 10, p. 85, we should have between the earth and
Mars a thin attenuated nebular plane, in which local conden-
sations would occur similar to that before suggested for the
system of asteroids ( 112). Under certain local conditions
such condensations may have assumed any possible dimen-
sions of mass according to the amount and disposition of the
surrounding nebular matter and to its initial motion being
directed so as to form a centralized system or otherwise.
Upon these conditions any local condensation would form
separately what we may term a small planetoid, or merely an
isolated unit of impalpable dust.
FORMATION OF LAND-AREAS. 161
The units of discrete solid matter formed within the space
above defined, capable of composing any part of the future earth,
must have possessed at the time of their formation a revolution-
velocity less than that required for a circular orbital motion,
according to the law of orbit. Otherwise they would have
maintained their orbits and still circulate round the sun, a
possible condition at present for many of these condensations.
If the condensed matter was endowed with a velocity less
than the above, as before stated, the sun's attraction would
draw the early condensations into elliptical orbits ; and
consequently such as had a perihelion distance from the sun
within the distance of the outer periphery of the earth's nebula-
zone at the time must have fallen into this zone and have
combined with it, through the resistance which such projection
would encounter in passing into or through the nebula-zone.
In this case it is easily seen that solid matter projected into
the earth's nebula-zone must have combined motively with
the momentum of the matter of the zone, and, if it retained
its distinct solid condition, fall in spiral paths sunward, unless
it was drawn by a stronger local attraction within the zone-
ring or the nebulous globe of the incipient earth.
223. The period when exterior condensation would
intrude into the earth's nebula-zone would depend upon
many conditions. If its perihelion passage was entirely
resisted by the zone it would enter a part of its system ; but
if the resistance was insufficient, on account of the small
density of nebular matter, it might continue its projection
with an orbit of changed ellipticity in any degree. If it
arrived at perihelion within the zone-ring after the ring had
condensed into globular planetary nebulae or into a single
nebular globe, its perihelion passage might strike or miss
this nebula, or later miss the new-formed earth upon its
further condensation in such a manner that there may be
remains of intra-Mars condensations still falling as meteorites
across the earth-orbit owing to want of former coincidence of
M
162 NOTB6 ON THE NEBULAR THEORY.
perihelion position with the earth's place at the time of
internal conjunction.
224. Under the above-stated conditions, during the discrete
condensation of intra-Mars nebular matter and its projection
earthward, so far as this could overcome the resistance of the
nebulous matter to continue its projection in a solid form, it
would form earth-surface matter in combination with the
nebular earth-zone which would still be forming. By this
entire effect, the surface of the globe would receive a mixed
condensation of matter upon its surface composed of the
discrete matter, which would contain every form of solid
elementary matter, and of the residual nebulous matter that
was condensing at the period.
The above-defined mixed conditions of deposition correspond
fairly well with actual observed conditions, as it is clear that
we have no regular density system such as would be pro-
duced under the condensation of a purely nebular system.
We have gold, copper, iron, and other dense metals upon the
surface, which may at an early period have formed the central
systems of discrete condensations from the universal pneuma
before their projection to the earth.
225. In the small amount of exterior matter that has fallen
upon the earth in recent times we have been able to recognize
the presence of 23 elements, for the greater part those that
generally prevail upon the earth, but in a few cases some of
its rarer elements. They show upon the whole that they are
condensations from an original universal nebula, in which the
heavier as well as the lighter elements appear, iron largely
predominating. The mean density of the entire mass of such
meteors as have fallen to the earth in modern times is possibly
not far different from the mean density of the earth, about
5*6 times that of water, which should be the case under
purely open nebular conditions of condensation from a
universal pneuma system.
It cannot, however, be suggested that the presence of
FORMATION OF LAND- AREAS. 163
heavy metals upon the earth's surface is entirely due to its
reception of meteoric matter. There are other sufficient
causes made quite evident in special cases. Metallic veins
appear in many cases to be caused by the evaporation of
metals from the heated interior, through fissures which were
produced by the upheaval of primitive and later rocks. This
evaporized matter is either in the form of pure or alloyed
metals or of haloid compounds often modified by the presence
of heated water and possibly originally combined in gaseous
emanations. There is another cause to be proposed further
on, namely the effects of the loading of ice at the poles upon
the central system of the globe, causing projection of interior
matter; so that the formation of land by the inclusion of
meteorites may not be thought to be even a necessary
condition of its formation, but only a very probable factor.
226. To recapitulate the condition proposed that possibly
will agree with observation of geological structure : We
may assume that after the formation of Mars at the limits
of the sun's nebular periphery, planetoids were again formed
somewhat similar to our asteroid system existing exterior to
Mars, from condensations due to the reduction of the tem-
perature to the critical temperature of the sun's nebula within
a thin peripheral plane, M, E, fig. 10, p. 85. We may assume
that these planetoids were formed at first of the more
refractory nebular materials. That they moved at first in
their partially free orbits in spiral paths sunward under the
resistance of the residual, more attenuated, or less refractory
nebular matter that remained by its elasticity above the
denser part of the nebula nearer the sun's surface. That upon
further shrinking of the sun's nebula and fall of temperature
in a more regular manner, the earth's nebular zone was first
formed as a mass extending in volume much beyond the
moon's orbit under conditions already discussed. That this
condensation, which finally formed the earth, was set in
rotation consistent with its mode of formation due to the
M2
164 NOTES ON THE NEBULAR THEORY.
difference between the linear velocities of its outer and inner
parts, which were moving at equal angular velocity, as before
discussed ( 146).
227, That under the above-stated conditions, the nebulous
earth, being of much larger mass and condensing much later
than the outer small planetoids, remained gaseous for a long
time after they had condensed. That it became a liquid
globe surrounded by a voluminous nebulous atmosphere at
the time that the intra-Mars planetoids represented in minia-
ture cold bodies similar to the present earth. That these
planetoids after cooling possessed dense metallic centres,
probably still highly heated, surrounded by oxidized metals
and haloids, with water or, more probably, ice and air upon
their surfaces. That the planetoids moving under the resist-
ance of the still attenuated nebula surrounding the sun with
their small excess of angular velocity, drifted slowly as regards
inward motions sunward into the nebula of the new-forming
O
globe until they were drawn to its surface and became finally
incorporated about the perihelion positions of their orbits.
The effects of the percussion again developing great heat, but
not sufficient to convert the perfectly cooled planetoid pro-
jected upon the earth's surface, if this was of large mass
again into a liquid state, or to bring the earth and the
planetoid back to the form of a single nebulous globe.
228. Such systems of collisions as inferred above at every
union of a planetoid, if this happened to be of large mass,
might be considered to form at the time of contact a close
binary system. The parts of the planetoid in contact with
the earth would become highly heated by the effect of the
collision, and sinking with its lighter coating into the liquid
central globe of the earth would produce convection currents
during its immergence, bringing the lighter liquefied surface
matter into equilibrium of the mean gravitation system. In
this process the lighter oxidized matter from the former buried
surface of the injected planetoids being slowly floated up to
PLANETOID COLLISION WITH THE EARTH. 165
the surface of the earth would remain projecting beyond its
mean spherical surface, so as to form a future land-area.
The extruded oxidized mineral matter of the planetoid
would carry with it part of the metallic matter that forms the
interior of the earth. Thus, through the friction of the opera-
tion and cohesion, such dense matters as gold, platinum, and
other metals formerly in the core of the planetoid would he
placed much above their mean gravitation position on the
earth's surface.
229. The condition of our planet after the period of the
last collision of a planetoid of any considerable mass would
be most probably represented by an irregular spheroid sur-
rounded by a nebulous atmosphere, still in a highly heated
state from the temperature due to its original mode of forma-
tion and from that developed by the collisions of the planetoids
from which certain factors of its land-areas were possibly
derived. We may consider a particular case.
230. Projection of a large intra-Mars Planetoid upon the
Earth. We will assume for the formation of a continent for
a special case that a cold planetoid came into collision with the
earth at the position of South America, which was of a mass
greater than this continent, measured above the level of the
ocean. That the planetoid moved in a spiral path under the
resistance of the earth-nebula in the same direction as the
earth's rotation, so that it reached the earth with what we
may term a very moderate percussion. That the earth at the
time was a liquid metallic globe, covered only by a thin
coating of oxidized matter. The effect of the concussion
would be that the surface of the cold planetoid would be
raised to a white heat ; its water or ice would evaporate into
the nebulous matter about the earth ; its oxidized surface
would sink at once into the liquid earth-globe and become
liquefied itself. This lighter liquefied viscous matter of the
exterior surface of the injected planetoid, composed mostly
of silicates as in the earth-system, would be floated up slowly
166 NOTES ON THE NEBULAR THEORY.
about the periphery of the intruded mass, and the solid centre
of the planetoid would gradually sink into the globe until it
reached a position of gravitation-equilibrium and became a
part of the interior metallic density-system of the globe. This
could not occur, however, without much confusion and violent
plutonic action within the central matter during the time that
the lighter oxidized former surface-matter of the planetoid was
reaching the permanent surface of the globe by convection
currents. These currents would form special drifts and
bring much of the metallic matter to the surface by tearing
it away in collision, as it is a property of semi-fluid siliceous
matter to bite into a metallic surface, as we find in the
process of enamelling.
231. The final result of such a motive system as here
presented would be the projection of a mass of vitreous rock
above the earth's surface, entirely added to the earth's super-
ficial system, forming a hollow plane, produced by the excess
siliceous material floated up at the periphery of the included
planetoid. The lowest part of the surface of the earth
covered by the projected planetoid would be raised above
the mean gravitation-plane of the earth's surface, the entire
upheaved rocks being in equilibrium-excess of mass of the
volume of the vitreous rocks upon the surface of the partially
included planetoid. The effects of the inclusion of a planetoid
upon the early globe as herein described may be better
shown by a diagram. Let fig. 22 A be the metallic core of
the planetoid; 6Z/the surrounding tertiary matter; cc'the
surface of the globe ; d d' d" the mass in section of the
tertiary matter finally resting above the surface of the globe ;
1 1' and t" t" 1 will show the lines of greatest mass that will
rest above the surface. The tertiary mass in segment of arc
z z' in a heated viscous state would float round the denser
core and finally appear upon the earth at d and d'. The
extruded tertiary matter would generally finally rest in
gravitation-equilibrium with a part of its mass sunk in the
PLANETOID COLLISION WITH THE EARTH.
167
matrix matter of the globe, and being vitreous it would also
tend to run down upon the surface, but in its early extrusion,
being at the same time subject to the radiation of heat when
projected much beyond the earth's surface, it would partially
cool down and finally take a mean gravitation position in
relation to the dense metallic core of the earth with con-
siderable projection therefrom.
Fig. 22.
232. As the planetoid may be assumed to strike the globe
near its equator, it would have more of its matter included
upon the equatorial than the polar side of contact. The
plutonic mass would therefore tend to extend poleward,
diminishing its volume so as to leave the continent due to
its projection of pear-shaped outline, with its broadest end
towards the equator.
233. The cold planetoid falling towards the earth-centre
would leave its upper surface exposed for a period, and this
shutting-offthe radiation from the highly-heated globe beneath
would cause a rapid deposition by condensation of the super-
168 NOTES ON THE NEBULAR THEORY.
imposed nebula, so that it would acquire a heavy surface-
stratum of new deposition beyond that of the planetoid's mass.
234. In the above we have taken an extreme case, The
special condition of the fall of small bodies of meteoric matter
could not have produced distinct features upon the earth's
surface. If meteoric bodies fell in swarms, the effects would
be the same as those just considered for single planetoids,
but probably with more dispersion upon the earth's surface.
The general detached fall of single small meteorites could only
produce a certain amount of incidental inclusion of that which
appears to be foreign matter to the system of stratification
wherein it fell, which is recognized by geologists.
235. It cannot be assumed that the foregoing conditions of
projection of large planetoids could remain permanent, being
since subject to long periods of atmospheric denudation and
all the after- conditions of our globe, of which we have full
knowledge by geological evidences that remain in volcanic and
stratified rocks ; but upon the whole the initial setting-out of
the globe in local land-areas, if it occurred by the inclusion of
planetoid matter in the manner proposed, could never be
eradicated. The forms of ancient continents have no doubt
been modified in time by atmospheric conditions, and by the
effects of oceanic currents, through the direction given by
solar impulse, causing wear in their projecting parts and
deposition of matter in quiescent contiguous water, owing to
which the great ocean-basins at the present time approach
circular areas of circulation of free oceanic surface, which I
have considered in my work on fluids * (fig. 22) . Under these
conditions the central continental matter may in some cases be
undisturbed. The general mass of vitreous matter, localized
in great depth of rock by such projections as suggested, could
never be entirely distributed by forces known to us as having
been active upon them.
* < Fluids,' 1881, pp. 354, 377.
[ 169 ]
CHAPTER XII.
HYPOTHESIS OF THE FORMATION OF THE EARTH UNDER
PURELY NEBULAR CONDITIONS.
236. Earth-formation under Nebular Conditions only. This
was proposed ( 204) as the most important factor. The
proposition of land-formation from discrete matter given in
the previous chapter may be considered as purely incidental,
affecting certain land-areas and occurring at indefinite
periods. On the other hand, the conditions of nebular con-
densation to form the earth must have been constant during
the radiation of its initial heat at the time that such nebula
could form a dense atmosphere around the earth. It will be
therefore convenient for distinction and simplicity to consider
this nebular condition separately as regards its entire effects,
neglecting for the time the conditions which have been already
discussed of incidental incorporation of solid planetary matter
with the earth. This will not change the discrete conditions
of projection of matter before proposed, which must have
entered into composition with the nebular conditions now to
be considered, as it is in this combination only that we can
have the entire evidences of the actual conditions satisfac-
torily explained.
237. We have already considered many modifying con-
ditions that may have been active during the formation of
our earth, particularly in the effects of the state and condition
of the sun at different periods. Yet we must assume that
there was a general or uniform system of condensation of
170 NOTES ON THE NEBULAR THEORY.
the nebula which formed the earth due to radiation of its heat
only into space, upon which the varying outward conditions
of the state of the sun would he superimposed. Under such
purely nebular conditions we will assume for the present
that the sun's condensation may be taken as a constant, and
that the temperature of the earth's nebula was decreasing at
a uniform rate. The more special condition of variation
will be considered in the following chapters. The factors of
purely nebular conditions will be most conveniently taken
under separate headings.
I. Period of dissociation of elements onward to the time
of the early condensations which were adapted to
finally produce the globe in a liquid form.
II. Period of condensation of volatile metals, association
of oxygen and the halogens with metals and metalloids
to form the earth's crust.
III. Period of deposition of water.
IV. Period of deposition of snow and of ice formations.
This last period is very important in completing the causes
of changes that have passed; although in this we go beyond
purely nebular conditions, still the mode of action is con-
tinuous. This subject may be better considered in a separate
chapter.
These periods, although it is proposed to take them
separately, run necessarily the one into the next by inter-
mediate stages, as the separate systems defined depend upon
the effects of time which is continuous.
238. I. Period of Condensation of Highly Refractory
Matter. At the commencement of the first period suggested
above, we may assume that, immediately after the separation
of the earth's nebular ring from the sun's nebular system,
the heat at this time may have been sufficient for the disso-
ciation, at least so far as a gaseous or vapourous condition,
of that which was to become terrestrial matter. At such a
time, if the nebular ring were denser in any part or if it
CONDENSATION OF THE EARTH. 171
were broken by any disrupting cause, such as the intrusion
of a comet, a local density system would be formed in some
part, which would then become the nucleus of our earth.
The ring of nebula after its detachment from the sun is
assumed to be in equilibrium in its mean orbit, so that all
parts of its matter would drift slowly towards any denser
parts by consecutive attraction of its near parts. In such a
system if the nucleus was formed by heavier heated matter than
the condensation of the exterior nebulous matter, this would
drift thereto and approach the centre in convection currents.
These currents would be constantly active in proportion to
the difference between the density of the central system and
that of the surrounding vapours or gas to cause the speci-
fically heavier vapours, as, for instance, those of the heavier
metals, to move through the minor resistances of the lighter
gases towards the centre of the svstem. At the same time
o /
light elastic gases would be buoyed up to the extreme outer
circumference of the system. This is exactly the case at the
present time with the exterior of the chromosphere of our
sun, which we find surrounded by hydrogen, the lightest
known element, with denser gaseous and vapourous matters
placed concentrically beneath *.
239. Immediately following the first condition of an exten-
sive nebulous or gaseous atmosphere surrounding the new
globe-system forming from the continued process of radiation
of heat, there must necessarily come a period of con-
densation of the nebulous matter to liquid or solid matter.
Whenever this period arrived it would be quite indifferent
in what part of the nebulous ring system about its exterior
surface the condensation occurred. The condensed matter
would, by its superior specific density, immediately pro-
ceed to pass through the lighter gaseous parts towards the
centre of gravity of the system, even although the system
* Lockyer, ' Studies in Spectrum Analysis,' p. 147.
172 NOTES ON THE NEBULAE THEORY.
might remain almost entirely nebulous, just as rain passes
through the atmosphere. Thus, if we imagine the platinum
group of metals to be widely diffused in the nebulous state,
these would not only tend to take a central position by
gravity, but in all possible condensation through exterior
radiation they would flow towards the centre. Particu-
larly in this case, as such matter as platinum would have
little affinity to unite with the oxygen or halogens present
through which it might pass. Further, this metal would
condense at a temperature so high that the more general
matter prevailing would remain gaseous. Like conditions to
those just explained for platinum would hold also with all
other dense refractory elements, causing constant exchanges
of relative gravitative positions throughout the long period of
condensation until the densest and possibly the least oxidable
of the original nebular matter formed a considerable globe.
240. Whatever may have been the composition of the
early condensations or primitive liquid matrix which formed
the early earth, whether this was metallic or mineral, in the
ordinary sense of the term, one thing is certain, that the
present crust as we know it is very largely composed of
metallic and siliceous oxides. It is therefore reasonable to
suppose that oxygen, being lighter in its pure or gaseous state
than the average mass of the early nebulous globe, remained
in the early highly heated nebula an exterior element, and
that compounds or oxides derived therefrom were deposited
at a later period than the refractory metals.
Under the above conditions, assuming that the denser,
more refractory matters continually condensed about the
central system or globe, this condensation might occur even
while the surface maintained an almost incandescent tempera-
ture ; so that possibly at a period when the earth measured not
less than within 400 miles of its present diameter, it was still
a liquid globe at a white heat comparable in temperature at its
surface with that of the lavas which issue at the present time
CONDENSATION OF THE EARTH. 173
from our volcanoes. At this period the globe would necessarily
be surrounded by an atmosphere which contained as a part
of its earliest gaseous density arrangement nearly al| the
oxygen, chlorine, and hydrogen of our system, together with
all other elements which remain gaseous at the high tempera-
ture now considered, except only such part of them as might
be condensed or combined near the surface of the globe
by the enormous nebulous atmospheric pressure then prevail-
ing. The globe, unless disturbed by collisions with exterior
matter, would be at this time an incandescent smooth uniform
liquid spheroid, without any projections upon its surface.
241. From the mean density of the earth, 5*6, it is highly
probable, as before proposed, that the central matrix is entirely
metallic. Under this condition, however distinctly the con-
densations might form at the earliest stage an increasing
density system towards the centre, the tendency of metals
to form alloys would materially modify this during the
after condensation of the lighter metals. Further, the heat-
conducting powers of the metals would tend to keep the
globe at a uniform temperature to a depth below the point
where matter could experience the effects of radiation.
There is no reason to suppose that these conditions have
been materally modified as regards the greater part of the mass
of the earth up to the present time, as there could not have
been great loss from radiation during the time that the earth
was surrounded by a dense nebulous coating which was
giving out its heat on continuous condensation, nor after the
oxidized coating had condensed to form our present highly
non-conducting surface, as this would give out great heat
upon its oxidation. Therefore the probability is that the
loss of central heat was and is largely operative only in con-
densing or thickening the surface coating, under conditions
which will be discussed further on.
242. At the period when the earth was wholly liquid the
outward diameter of the sun or his photosphere probably
174 NOTES ON THE NEBULAB THEORY.
extended much beyond the orbit of Venus. At this time
the earth was possibly outwardly a self-luminous globe partly
obscured and surrounded by a moon-ring or nebulous moon.
Possibly also the planet Jupiter was not wholly condensed,
but appeared as a large heat-giving nebulous body dispersing
a small part of this heat to the earth. Under these conditions
the earth's equator by reciprocal radiation-of-heat exchanges
with the sun, and in a less degree with the other planets, main-
tained nearly its initial temperature for the time. The polar
regions being open to space would be radiating their initial
heat more rapidly than the equatorial regions, thereby re-
presenting the area of cooling surface to which condensing
nebulous matter near the earth's surface would drift in aerial
currents, a condition which, as regards the vapour of water,
has remained to a certain extent permanent.
243. II. Period of Condensation of Volatile Metals,
Association of Oxygen and the Halogens with Metals and
Metalloids. We may now consider the conditions of a period
when the sun's photosphere had shrunk to nearly the
orbit of Venus, and heat exchanges within the planetary
plane had grown much less active ; when the polar regions
through radiation of their initial heat may have been reduced
to a red heat and assumed a viscid consistence. Under these
circumstances, by the continuous radiation of heat from
the exterior nebulous surface or atmosphere, and the cooling
by radiation of initial heat from the surface of the globe,
volatile metals would be deposited and oxygen and the
halogens would approach more nearly to the earth in its
nebulous atmosphere, by which means their association with
metallic vapours near the surface would be possible and
might even be rapid. At this period, under the great
nebular atmospheric pressure then present, the new-formed
oxides would fall as rain over the cooler polar regions, where
the surface heat could not support the vapourous state ; and
we may assume that at their great heat they would remain
CONDENSATION OF THE EARTH. 175
in a viscous state, and therefore would flow outwards from
the cooler polar regions towards the equator to gravitative
equilibrium, combination with the central matrix being no
longer possible, as in the early conditions with prevalent
metallic surface matter.
244. In continuity of what is here taken to be the same
period we come upon conditions most important to geology,
namely when it became possible as a natural result of the cooling
for solid oxides, when they formed tertiary matter, to rest upon
the surface of the globe. This occurred at first possibly as a
kind of oxidized scum, such as we find floating in the ordinary
melting of metals exposed to the air, and no doubt only over
the colder area of the poles as just stated. The presence of
such a scum acting immediately as a non-conductor of heat
would shut off a part of the initial radiation from the surface
of the central matrix of the earth, which previously kept the
gaseous matter above it from condensation at nearly its
critical point. This loss of the support of radiated heat from
the earth would cause the condensation of vapourous and
gaseous matter to appear as dense clouds and finally to pre-
cipitate the condensed oxides, of which the clouds were formed,
upon the cooler polar areas of the earth. Under these con-
ditions, as soon as a cooler primitive scum was formed, this
would be immediately covered by further nebulous deposition
of oxidized matter.
245. As the polar regions of the earth cooled down through
open radiation the early basic matrix would no longer main-
tain sufficient surface-heat to retain a liquid surface, and the
early siliceous oxides would become by loss of heat stiffly
viscous. After this period, the same oxides that fell at great
heat in a liquid or viscous state might fall over the cooler
areas as a kind of tertiary mineral snow, and in this way
cover up the primitive viscous scum, possibly even to very
great elevation. At the same time this would depress the
supporting liquid and the viscous surface beneath, causing
176 NOTES ON THE NEBULAR THEORY.
this surface-matter to move outwards from the poles to equi-
librium of gravitation by displacement. In this manner
gravity would spread out or carry the newly-formed oxides to
great distances from and around the poles.
246. In the above scheme it is assumed that oxygen and
other elements of low specific gravity at a high temperature
could not reach the earth for combination with denser metallic
matter at any early period of condensation. But if we suppose
there were certain combinations which would be precipitated
at any given temperature from the nebula, even before the
complete metallic matrix was formed, their specific gravities
would still maintain them as a scum, and the after con-
ditions, as already described, would not be materially modified.
247. Long after the deposition of the more refractory oxides
considered above, we should naturally have the deposition of
the more volatile chlorides, and in a less degree the fluorides
and iodides, and generally we should have the most volatile
matter of the solid earth longest in suspension in its primi-
tive nebular atmosphere. At this point it therefore becomes
important to consider what bodies in combination may have
remained gaseous at a moderate temperature capable of finally
contributing to the matter of the earth's crust, which we
may assume, from the presence of their elements in the
early rocks, were possibly largely diffused previously to the
formation of our present atmosphere. Of these gases as
most important we may take :
Aluminium Aluminic chloride, A1 2 C1 6 .
Iron ... Ferric chloride, Fe 2 Cl 6 .
Or, descending to our present atmospheric temperature, we
have:
r Silicic hydride, SiH 4 .
Silica < chloride, SiC 4 .
(. fluoride, SiF 4 .
PERIOD OF CONDENSATION. 177
r Carbonic oxide, CO.
Carbon -3 Carbonic dioxide, C0 2 .
C Carburetted hydrogen, CH 4 .
Sulphur . ( Sulphurous anhydride, S0 2 .
(.Sulphuretted hydrogen, H 2 S.
248. To which we may add the vapour of water. In some
cases one of these gases would decompose the other and cause
deposition. There are other compound gases, less important
in a geological sense, that would remain constantly present
at a somewhat higher temperature. There is an omission
in this volatile series of two very prevalent surface materials,
calcium and magnesium, the chlorides of which are gaseous
only at high temperatures. But the oxides of these bodies
are so extremely light, that assuming they condensed with the
heavier siliceous oxides they would fall very gently through
a dense resisting medium, such as the nebulous atmosphere at
this period is considered to be. Further, from these oxides
being very light and refractory in a finely-divided dry state,
they would remain upon the surface and drift about in the
dense aerial currents then prevailing, and rest finally in
positions above the heavier siliceous and denser metallic com-
pounds, which would be for the greater part condensed at
the time. Under any conditions, by their specific gravity
they would take finally a surface-position upon the primitive
scum. The condensation of the above-described compounds
with others present, possibly formed a considerable part of the
superficial crust covering the earlier deposited oxides; but
at this time we commence to have the interference of water
condensed in large volumes, which was instrumental in many
changes to be considered further on.
249. Formation of Continents. We may now consider the
effects of the above-described formations generally upon the
earth's crust as influencing the formation of continents,
under conditions of nebular condensation only. We may
N
178 NOTES ON THE NEBULAR THEORY.
take it that at the period when oxygen and the halogens
entered into association with the prevalent basic metals, their
oxides were first deposited over the cooler polar areas upon
principles just discussed, that all the surface of the globe,
except the polar regions which were most open to radiation,
was in a highly heated liquid state, and the whole substratum
of the polar area in this state also. Under these conditions,
as the oxides condensed about the cooler areas of the poles
this lighter oxidized matter, its lower part being in a plastic
viscous state loaded up as it might be by condensation at the
poles to great height, would have through the influence of its
gravity a constant tendency to be pressed outwards from these
regions, so as to float upon the surrounding liquid metallic
matrix into lower latitudes. At the same time, by natural
affinity these oxides would cohere together, more particularly
at the base of the mass, where the internal heat and pressure
would maintain them in a liquid viscous state. Thus as the
compound oxides accumulated in mass they must of necessity
have overflown or be thrust outwards from the cooler polar
regions from their own internal gravitation-pressure, and in
this manner form coherent projections, taking the lines of
least resistance in moving upon the liquid or semi-liquid
metallic matrix constantly towards the more highly-heated
regions of the equator to restore gravitation-equilibrium. This
thrusting-out would occur exactly in proportion to the accu-
mulation of the lighter condensed oxidized matter from its
increased pressure through constant deposition at the cooler
area of the poles.
250. The form which the above- described coherent pro-
jections of oxidized matter would take would be that of long
tears, precisely the same as that of the boundaries of a melted
metal or other cohesive liquid poured out continuously in bulk
upon the centre of an extensive heated level slab. This form
would, however, be modified to a certain extent by the re-
melting of part of its extreme prolongation, particularly at the
FORMATION OF CONTINENTS. 179
thinner bordering edges in approaching the more highly
heated, that is the less cooled, equator. These prolongations
from the polar regions would therefore take the final forms
of pointed tongues, maintaining a wide base upon the polar
regions and diminishing gradually as they approached the
still almost incandescent tropics, where heat would be partially
held from radiation by the large predominant sun.
251. Under the above conditions there would be also present
a constant tendency to widen the base of the prolongations
above described. Firstly by the extension of the solid surface
of the polar regions through continued cooling and the
increase of the amount of support to the elevation of oxidized
matter through submergence of the lower parts. Secondly,
by the deposition of a greater amount of nebulous matter,
which would increase proportionally to the surface shading
from the influence of the radiation of the earth's initially-
heated matrix, so that from both these causes a constantly
wider area of base would be added to the floating prolongations
as they were pressed outwards from the polar regions, making
the entire projections of conical form. At the close of the
period above depicted, so far as condensing nebular conditions
were concerned, the whole of the new-formed land-surface,
derived from the deposited oxides, would consist of pointed
areas of projection extending towards and over the equator,
proceeding from an elevated base spread over a wide region
around the poles. The new land in lower latitudes would
appear as a floating mass, possibly of a dull red heat, upon
a liquid matrix of much greater density and more highly
heated than itself.
252. We may now consider a period when the whole
surface of the globe proceeding from the poles began to set
to a viscid resisting surface as an effect of the radiation of its
initial heat into space, and when the new land-surface in
pointed continental areas had become superficially rigid. At
such a period the central areas of the new land, being pro-
N2
180 NOTES ON THE NEBULAR THEORY.
tected by a non-conducting coating from excess of radiation
from the still highly-heated matrix beneath, would possibly
retain a semi-viscid condition at a small depth. We still as-
sume that mineral matter is being deposited, although more
slowly, from space, especially at the cooler areas of the poles
now assumed to be much below red heat. Then, however
much mineral matter should be piled up at the poles of the
earth, it would be more and more resisted at the borders
of the now viscid surface of the matrix surrounding the
new continents. Under such conditions possibly the edges
of the new-formed continents would be pressed up and
contorted by the resistance to further projection and have
their borders thrown up much beyond the average surface,
such edges being continually cooled and consolidated by
their exposure to radiation at the greater heights. New
smaller tongues of projection might break out here and there
at any points of least resistance for the escape of the internal
pressure of the semi-liquid oxides flowing to equilibrium.
253. At a later period, when the floating movement of the
continental areas became quite impossible by the resistance
offered by a considerable depth of the cooled surface of the
matrix and oxidized magma above, and the various matters of
the nebulous system were mostly deposited, the more heated
interiors of continents then formed where the polar outflow
was most continuous, would contract and sink down in cooling,
and leave the new land-areas, although of great altitude, of
basin-like section.
254. Distribution of Land-areas. To summarize the con-
ditions here proposed : the continents may have been fully
delineated before water yet filled the oceans, these appearing
as pointed land-systems proceeding equally from each of the
polar areas ; but if we consider the actual condition we find
we have very little land in the southern hemisphere and much
in the northern. There must, therefore, have been, even at
this early period, some modifying conditions to those now
DISTRIBUTION OF LAND-AREAS. 181
generally proposed to account for this. What such conditions
were has been already suggested upon the precipitation -theory
in the last chapter. They might possibly also, perhaps less
logically, be suggested upon the nebular theory simply.
255. If at the period when the earth was still an incan-
descent globe, we assume that radiation of heat from any
cause might have been greater in the northern than in the
southern polar regions either from there being cooler space
towards the northern pole or from deficiency of heat- radiation
from distant celestial bodies, or from excess of winter eccen-
tricity of orbit at the time, or other causes sufficient to chill
this pole first, then the first accumulation of oxidized
deposits would immediately shut off radiation of initial heat
from the early matrix of the globe into the superimposed
nebulous matter and cause its precipitation at this pole only ;
and as the area thus shaded from internal radiation by the
first early deposits would constantly increase in dimensions
proportionally to the depositions, the pole first chilled by
any cause would become in increasing ratio the greatest area
of deposition. In this manner the land-forming oxides might
be deposited at the north pole in quite sufficient excess to
account for the difference we find at present between the
amount of land-surface in the northern and that in the
southern hemisphere, or be even sufficient to disturb the
position of the centre of gravity of the earth's mean volume.
So that at the present time the superficial subaqueous region
of the south pole may be of much denser matter than that of
the north where the early oxides were most deposited, which
condition must continue permanently.
256. If we now take cognizance of the present form and
distribution of land-surface and oceanic basins, and make
allowance for all reasonable changes, volcanic and other,
that the immensity of time must have brought about be-
tween the periods already discussed and the present, we may
ask, Is the distribution of land entirely consistent with the
182 NOTES ON THE NEBULAR THEORY.
theory proposed upon nebular conditions only ? This would
be very difficult to answer in the affirmative, but we may find
that in certain points there is agreement, which may possibly
be all we may expect after so great a lapse of time, and with
other factors of formation that have been already proposed.
257. By the nebular system here suggested, we should
have a mass of land at the north pole from early condensa-
tions, and a less mass at the south pole from later condensation.
Both of these land-areas would possess pointed prolongations
extending outwards to or possibly even over the equator.
Of the actual land-areas which may be considered as consistent
with the principles discussed in this chapter, we may take the
prolongations of land in North America with arctic base, the
lesser prolongation of Greenland, the prolongation of the
Europseo-Asiatic continent to Mocha, that of the peninsula of
India within the Ganges, and that of Siam, extending at one
time possibly to Sumatra. We now find the most important
areas of S. America, Africa, and Australia disconnected from
polar areas. But as regards Africa, if we take a wider view,
this may be considered as a prolongation of the Europseo-
Asiatic area, leaving then only the difficulties of accounting
for the division of the narrow Mediterranean and Ked Seas.
In the same manner, Australia having the broadest base to the
south, we may imagine it to have been once connected with the
antarctic polar system. At this period its area would extend
in pointed form, including and possibly extending beyond
New Guinea. The principles discussed leave South America
an entirely detached continent, which, considering its theo-
retical form upon the nebular principles just proposed, would
indicate that it must belong to the northern area, but we
now find it in the southern. Therefore, this may possibly be
better accounted for upon the discrete conditions previously
suggested.
258. It is not probable that the early conditions of earth
DISTRIBUTION OF LAND-AREAS. 183
formation could be fully recognized, as very material changes
must have occurred since. The anomalies to the theories
proposed of the detachment of S.America, Africa, and Australia
might possibly be met in a certain degree by supposing that
these cohesion systems were detached from the area of their
polar condensations and drifted when the earth's metallic
matrix was still superficially liquid into their present position.
This might have been caused by outward pressure from the
poles, of matter which condensed at a certain period, but
afterwards dissolved in the highly heated waters, deposited
in great volume and under great pressure, which will be
presently discussed. Taking all these matters into consider-
ation, however, it is not probable that nebular conditions alone
ruled, as there were no doubt also discrete condensations
about and without the nebular zone or ring, which in time,
through crossing orbits with the earth, came into collision with
it and materially modified the land-areas, possibly in the
manner discussed in the last chapter.
259. Following the above-described hypothetical conditions,
under which the basic superficial system of the globe may have
been formed, we have for the consideration of the present
continental forms to allow for the influence of forces acting-
onward to the present period, to which we must attribute great
modifications. Among such influences we have erosion and
after deposition on coasts, vulcanicity in its widest extent, and
the wear of oceanic currents, forming altogether constant
elements of modification with others to be discussed.
260. Whatever may have been the special or local con-
ditions of early continental formation, it is very probable
that at the close of the long period of deposition of oxide and
halogen compounds, or what we may term the dry period of
deposition, the land-areas were generally clearly defined for
all future time. If these oxides as non-conductors stopped
the radiation of central heat and at the same time radiated
184 NOTES ON THE NEBULAR THEORY.
their initial heat from the surface, the deposits would be
piled up over such areas, and by this loading press down
the lower surface of the land to gravitation- equilibrium, so
that the land of the earth may be represented as consisting
of masses of oxidized matter floating upon a lower denser
liquid metallic substratum.
261. From the immense volume of oxides known to exist
upon the surface of the globe, by the mode of precipitation
here proposed the land-areas may have attained great height,
possibly locally of ten to twenty miles. These areas, ob-
structive to radiation of internal heat, would advance from
the poles, so that afterwards deposition of oxides or halogens
over such land-areas would become general, and upon points
of elevation as great as over polar areas, in the same way
that snow falls on mountains at the present time. In such
new-formed depositions, generally pressing from their centres
outwards to gravitation-equilibrium, acting with deposition of
water, we have possibly the entire factors of the great gneiss-
forming age, -vestiges of which remain intact with all the great
displacements and contortions impressed upon it which are
still evident at the present time. This will be discussed
further on. The depositions about the tropical land-regions
which may have been produced by causes discussed in the
last chapter, would act in conjunction with the condensations
here considered and locally magnify their effects.
262. III. Period of Formation and Deposition of Water. It
has been calculated that the whole of the water upon the globe,
if equally distributed, would be about two miles in depth. If
this, at the temperature then prevailing, formed an atmosphere
about the globe it would produce a pressure of about 400
atmospheres, or 7000 Ibs. per square foot of surface. It is
unnecessary to say that this could scarcely occur at a time
when the earth's surface was even at a red heat, for at this
pressure water would possibly remain liquid even at a white
heat. Further, by the classical experiment of Cagniard de
DEPOSITION OF WATER. 185
Latour *, water at a temperature of 412 C. was found to
dissolve glass. Further experiments have shown that siliceous
rocks could not only be dissolved in water by heat and pres-
sure in the presence of alkalies, but be recomposed to form
quartz, felspar, and other minerals f. At the heat and pressure
then present, water would therefore combine with mineral
matter, which would be crystallized and become solid rock as
the temperature afterwards diminished. We must therefore
suppose no distinct definable line for the formation of water
on the globe, but merely make a broad assumption that it
probably formed after the deposition of the mass of the most
refractory oxides which could remain gaseous at a very high
temperature only. Further, there is no doubt that the
energetic action of the early highly-heated water would be
greatly increased by the presence of corrosive mineral acids
within it, which would be in a vapourous state at the same
temperature.
263. We may imagine at the first great deposition of water
which occurred at the cooler area of the polar regions, that
by its great solvent power when at great pressure it would
at once reduce and dissolve many of the oxides, and more
particularly the siliceous ones. That the streams produced
would channel out and disintegrate the solid elevated siliceous
deposits then covering the polar areas, forming great rivers, and
finally, by the heavy constant highly-heated rains, divide the
land up into detached parts or islands, carrying the dissolved
matter into the deep equatorial oceanic basins to gravitation-
equilibrium. That as the tropical areas by the conditions of
mutual heat-exchanges would be much more highly heated
than the poles, this water would again, for a large part,
evaporate over the tropics and leave behind the mineral
matters crystallized at the bottom of the ocean. In this
* ' Annales de Chimie/ IE. xxi. & xxii.
t Qeol. Soc. Trans, xv. p. 103.
186 NOTES ON THE NEBULAR THEORY.
manner the ocean bottoms would be formed from the debris
of the early polar condensations, and the polar areas would
become channelled and in time become largely oceanic by
this constant denudation and chemical action of the constant
drenching of the highly heated polar rains.
264. If we may assume that the process suggested above
continued until the sea reached to within half a mile or
so of its present level, the condensation of vapour might
then have become possible over the now much cooled lower
latitudes, and the elevated tropical lands possibly began to
receive a copious rainfall. It is throughout this period
until the ocean became of nearly its present level that we
may look for the greatest aqueous deposits upon all lands
in inland seas and shores together with a large deposit over
the bottoms of the oceans. The deposits as they were washed
from the coasts and inland would be left by gravity piled up
against the borders of the continents, and, generally by the
action of currents carrying mineral matter, irregularities and
depressions upon and about the continents would be filled up
or smoothed off *.
265. Of the gaseous matters previously considered as
possibly remaining longest in the atmosphere and incidentally
under decomposition forming surface matter ( 247), the
most important are the chlorides, and these are not found
largely in the earlier rocks, but in the ocean. The reason
for this is probably that they were decomposed in the presence
of oxide of sodium ; and as sodium does not form a gaseous
compound with chlorine at ordinary temperatures, it would
be at first precipitated on the earth from the nebulous en-
velope as one of the later lighter oxides, and this oxide after-
wards in the presence of water would decompose the chlorides
present, and still remaining in solution would carry the chlorine
to the ocean as salt, leaving its oxygen reunited with elements
* ' Fluids,' by the Author, p. 373.
DEPOSITION OF WATEK. 187
present which were not saturated to the highest or most per-
manent state of oxidation.
266. If we take the termination of the aqueous period to
be that at which ice was first possible of formation at the
poles, this would be the time of greatest general elevation
of the ocean ; for although we may suppose that a much
greater volume of water was held in vapour in the atmosphere
by the heat conditions present, still this would not nearly
equal the enormous amount of ice at present elevated at the
poles above the oceanic level which in the case assumed
would form part of the ocean. Dr. Croll * has estimated
that the melting of the antarctic ice-cap alone, considering
this as only equal to one mile in thickness, would raise
the general oceanic surface 200 feet. A mile is probably
much under the truth for the elevation of the interior of this
area; but if we add to this the arctic ice above sea-level, and
that of all elevated ice-clad regions, the general level of the
ocean would be raised possibly more than 400 feet from its
present surface, which, added to the present sea-level, might
indicate approximately the level of the ocean at a period
before ice was formed. Further, it may be presumed that
the constant deposition of water must have naturally reduced
the amount of land, so that the lower lands of the present
surface were entirely submerged.
267. This aqueous period, as will be hereafter considered,
possibly occurred in the palaeozoic age and also later in the
miocene period, when a temperate climate extended to the
north of Greenland. The general effect of these aqueous
periods upon what was at the time, and what afterwards
became, low continental land, was the heavy and almost con-
tinuous deposition of the debris of originally deposited matter
brought down by constant rainfall to the shallow coasts and
inland seas. This deposit upon principles suggested, although
* < Climate and Time/ p. 388.
188 NOTES ON THE NEBULAE THEORY.
less in proportion as it was distant from land surface, must
have been greatest towards the polar regions, partially filling
the oceans in these regions and generally diminishing towards
the equator. Therefore it is improbable that such enormous
deposits as the northern silurians will be found in the tropical
regions, their representatives being much thinner strata
derived from the ddbris only of the elevated continental lands,
produced entirely by causes already discussed.
[ 189 ]
CHAPTER XIII.
CONDITIONS OF THE COOLING EARTH DUE TO FORMATION OF
ICE AT THE POLES.
268. Pre-glacial and Glacial Periods. We have now to
consider the fourth period ( 237), when the residual nebular
matter surrounding the earth consisted, as at present, of air,
water, and carbonic anhydride. During this period, which
extends to the present, the earth-surface, from the effects of
the sun acting upon it, may be conceived to represent a heat-
engine in which the tropical regions are evaporating the
surface-water which is being simultaneously condensed about
the poles. Under these conditions the probable geological
effects of accumulation of snow about the poles will be now
estimated.
269. At what period ice could first accumulate about the
poles would depend upon the amount of secular cooling of
the earth's surface and the amount of heat received from the
sun. Difference in the effective amount of sun-heat might
be brought about either by diminution of his volume or by
clouding effects which may have occurred through condensa-
tion at any critical point of temperature of the solar nebula
( 95). The diminution of the sun's disc would be constant
and regular : the clouding effects would be exceptional and
depend upon the chemical constitution of the nebula at the
time. These exceptional conditions due to clouding will be
considered hereafter in another chapter ; the regular or
symmetrical condition due to the diminution of the sun's
190 NOTES ON THE NEBULAR THEORY.
disc will now be suggested. These symmetrical conditions
were discussed by me in a paper read before the Geologists'
Association, March 2nd, 1882, and are now reproduced with
some slight additions *.
270. Ice, of which we have the greatest mass at present,
under the uniform condition of condensation of the sun,
probably formed when his apparent disc was not more than
ten times his present diameter and when the mean surface-
temperature of the earth did not at most exceed its present
tropical temperature. At this period we had a much more
aqueous atmosphere than at present, as it is the law that the
quantity of vapour in the atmosphere when this is saturated
increases in geometrical progression as the temperature in-
creases in arithmetical. We had, therefore, probably at this
period, considering the relative areas of the globe under
tropical and temperate temperatures, a mean of about ten
times the present amount of aqueous vapour in the entire
atmosphere. At this relatively warm period as compared to
the present, we have only to imagine that a polar area became
sufficiently cooled through excess of radiation of initial heat
from the earth for condensation of water to occur in the solid
form of snow, and we have then the certainty of a continuous
copious fall of snow over the same cold regions during the
winter in the place of a former rainfall.
271. If we take the process of the cooling of the earth as
being quite gradual, omitting variations in the heat-giving
power of the sun which may have been brought about under
conditions already considered and other effects to be discussed
in following chapters, we may suppose that the cooling of the
earth sufficient for the deposition and formation of ice would
at an early period produce very little geological change,
if we omit consideration of all effects upon animal and vege-
table life, which would be materially affected by frost. The
* < Nature,' March 29, 1883 ; Proc. Geol. Assoc. vol. viii. p. 89.
PRE-GLACIAL AND GLACIAL PERIODS. 191
ice formed at this early period in the winter would be dissi-
pated in the summer, uncovering the land-surface and leaving
it at about the same level, except for a small amount of
denudation.
272. After the early period defined above, the immediate
effect of the further cooling of the earth from any cause,
astronomical or secular, would be the greater deposition of
snow in high latitudes, which as it constantly accumulated
in mass would slowly bring about the proportionate lowering
of the oceanic surface upon the entire globe from abstraction
of the surface-water. Under these conditions the littoral areas
formerly submerged in shallow water would be gradually but
slowly uncovered, until in the course of time the present
extent of land-surface appeared.
273. If we assume upon the symmetrical conditions pro-
posed, jbhat the entirely aqueous epoch closed with the miocene
period, when ice of the present system, due to decrement of
the sun's volume and other causes, probably began to cover
the poles in winter and melt in the summer, this would
evidently be the period of the greatest extent of oceanic
surface, for not only would the waters of the ocean be dis-
tributed over its surfaee to gravitative equilibrium, but the
land would have become largely levelled down by the heavy
rains of the earlier period, when the atmosphere was more
highly charged with vapour. When the elevation of ice at
the poles after this period slowly abstracted a much greater
part of the waters of the ocean, much of the shallow muddy
shores must have become soil adapted to vegetable growth
over the temperate regions.
274. The continuity of the oceanic depression upon the
conditions just stated and contemporary circumpolar elevation
by deposition of snow, as it changed the extent of land-areas,
must have affected the land-resistances to the direction of the
projection of oceanic currents, and with them the superimposed
air-currents, and have caused local variations of temperature
192 NOTES ON THE NEBULAR THEORY.
in polar and temperate regions by the direction given to these
currents due to heat and expansion of air and water from
the diurnal impulse of the sun *.
275. The elevation of snow to great height by condensation
at the poles would by its pressure upon the yielding mass of
the globe, whose equilibrium could only exist in a form
consistent with its gravitation and rotation as a spheroid
of revolution, cause an excess of pressure upon polar areas,
which would react upon the lower viscous superficial strata of
the earth and cause extrusion of viscous rocks to the surface
or the elevation of certain areas of the surface which offered
the least resistance to the imposed internal pressure until
approximate equilibrium of the rotative gravitation system of
the globe was restored. This elevation would be brought
about by the extrusion of felsitic or basaltic rocks to the
surface, or slowly in the upheaval of extensive land-areas, or
more violently in earthquakes and volcanoes, according to the
state of resistance due to the density, flexibility, or previous
faulting of the more or less yielding surface-rocks.
276. It must be impressed that the necessity for the main-
tenance of land-areas depends upon the elevation of rocks by
plutonic forces. Degradation by atmospheric forces and tidal
action is constant, so that unless the elevation is in excess of
the depression in the ratio of this constant degradation, land-
areas must constantly diminish by levelling-down, and, judging
from the quantity of sediment known to remain at present
in stratified rocks, all land-areas must therefore have been
wasted away ages ago.
277. The Distribution of Ice at the Poles. Under the con-
ditions discussed 245, the North Pole would be the first to
cool down for the deposition of oxides, so that deeper surface-
rocks would form at first at this pole. This deposition being
of a large mass of matter would disturb the centre of gravity
* 'Fluids,' p. 391 ; also Brit. Assoc. Rep. 1884, p. 723.
DISTRIBUTION OF ICE AT THE POLES. 193
of the globe, bringing it to a more northern position; the
effect of which would be that the surface-rocks of the South
Pole having the dense metallic matrix matter left nearer the
surface would represent altogether a denser mean gravitation
surface. The waters of the ocean being free on the surface
would flow towards the denser system of the South Pole
in equation with the density of lower matrix matter to
restore general equilibrium. At a later period, when both
poles were frozen, the aqueous evaporation-surface would be
greater around the South Pole, as it is at present ; and, as
the cold is assumed to be sufficient during this period at the
South Pole to cause the deposition of snow, it would be
greater in proportion to the surrounding area of evaporation.
So that the South Pole would gradually acquire and henceforth
possess the greatest accumulation of ice. Under these con-
ditions, as regards deposition of aqueous vapour, the phenomena
of excess of deposition of matter would be exactly reversed
from the earlier state when the North Pole received the
greater deposition of nebular matter, as before discussed.
278. The effects of the great accumulation of ice at the
poles may possibly be treated most demonstrably by con-
sideration of the present conditions, which represent the
terminal extreme effects of the present system of ice- formation,
so far as the uniform cooling of the earth has advanced. At
the same time we must recognize that the long interval, between
the earliest and latest period of ice-formation, must have
effected a great many changes upon the earth's surface, as
the resistance of the crust has constantly become greater
against deflection of its surface, by cooling through general
distribution of internal pressures, due to the local compression
of ice at the poles. Some suggestions with regard to this
point will be made further on.
279. Present Conditions brought about by Elevation of Ice.
With this general discussion of active conditions present, we
may now proceed to discuss the theory proposed upon these
194 NOTES ON THE NEBULAR THEORY.
premises of the effects of the action of elevated masses of ice
upon certain portions of the earth's crust. In the first place
there can be little doubt that there is at present a great
accumulation of ice at the poles of the earth. In the southern
ocean this forms a wall about the Antarctic Circle, according
to Sir James Ross, of seldom less than 200 feet above the
sea-level, where icebergs are constantly detached *. In certain
districts these are evidently of much greater height, as we
find large icebergs floating with the upper surface said to be
as much as 600 feet above sea-level, indicating a submergence
of probably five times this depth, or 3000 feet. As these ice-
bergs are detached from the front of the coast, it is quite clear
that the ice must flow down from the interior, as in the ordinary
glaciers ; therefore there must be heavy deposition of snow
accumulating at the back of them. Mr. W. Hopkins has cal-
culated that ice will just move downwards at one degree of
inclination. In taking the inclination of ice over some
mountain-valleys in the Grrindelwald glacier in Switzerland,
which is a very flat glacier for about a mile, I found that the
mean for the lower parts of this glacier was not less than two
degrees. The southern ice-cap includes an area approximately
equal to the entire Antarctic Circle, that is of about 700,000
square miles. Taking Mr. W. Hopkins's estimate, one degree
of elevation (as pointed out by Dr. Crollf), makes the altitude
of solid ice about 24 miles in thickness over the southern pole.
Such a thickness, assuming the ice by compression to take
nearly the solidity of surface-water, would represent a po-
tential force upon the earth's crust of say 3950 tons per
square foot about this pole, or taking an area of 10,000 square
miles of surface around the South Pole, a pressure upon the
crust in this region would be maintained of over 3900 tons
per square foot.
* ' Voyage to the Southern Seas,' Sir James C. Ross, vol. i. p. 219.
f ' Climate and Time/ p. 375.
PRESENT CONDITIONS CAUSED BY ICE. 195
280. We may consider further that it is scarcely possible
to suppose the ice a floating mass wholly breaking away
at the coasts or that it rests upon a level plane, the probability
being that the surface is extremely mountainous or irregular
inland near the terminal glaciers ; in this case we must allow
for greater friction on the motive plane, consequently for
greater depths of ice before slipping can occur. If 24 miles
of ice be assumed to continue in a static condition at the
South Pole, above the symmetrical earth considered as a
spheroid of revolution, it appears to be highly improbable
that the crust, supported upon a liquid matrix, could resist
this excess of pressure without deflection; and even if it
should do so, the accumulation of ice still remains a constant
factor until the resistance is overcome. We must further
consider that in Mr, W. Hopkins's experiment the free surface
of the ice was only a short distance from the artificial inclina-
tion measured *. It is possible that in the case of ice hundreds
of miles inland, in every way supported by surrounding ice,
grounded on a frictional or even possibly a surrounding
mountainous plane and at a much lower degree of temperature
than in these experiments, downward movements would not
be possible at one degree of surface-inclination. Under such
conditions ice might be permanently retained, if the earth
were sufficiently rigid, possibly at two or three degrees of in-
clination, as it is in our inland glaciers. With such a local
pressure upon a yielding sphere, which we assume the earth to
be, we can scarcely imagine the possibility of its resistance.
Further, ice in cooling increases in density, and we can
form no exact conception of its rigidity at 100 Centi-
grade, as it probably exists at this pole. Forbes's observations
showed that ice moved downwards in glaciers with velocity
somewhat proportional to its temperature f- Accepting all
* Phil. Ma<?. 1845, vol.xxvi.
t Forbes, 'Norway and its Glaciers,' 1853, p. 234.
o2
196 NOTES ON THE NEBULAR THEORY.
the conditions as active upon a deflectible globe, to cause
reactions upon its crust, then the elevation of land, earth-
quakes, and volcanoes could be easily explained. Similar
conditions to those defined for the South Pole would hold at
the North Pole, although at the present time less effectively.
281. Unfortunately the poles of the earth cannot be
reached for exact evidence of the above-assumed conditions
of accumulation of ice, but we happen to have in Green-
land a similar state active in a less degree and on a relatively
small scale. Here the inland ice being elevated above the
snow-line, vapour-currents are constantly condensing to snow,
which as constantly accumulates. So that the greater part
of Greenland is at the present time a complete glacier-
mountain of possibly 7000 to 8000 feet of interior elevation.
In the southern part we have at the present time land-
surface, and here the coast is now known to be sinking for
the space of 600 miles *. Exact measurements have not
been taken of the rate of sinking; but ancient buildings
upon the rock-islands are said to be sinking beneath the
ocean-surface, so that experience has taught the native
Greenlander not to build his hut near the water's edge f
282. It is very possible that the rate of sinking is nearly
proportional to the increase of weight of snow annually
piled up inland. Such pressure as may be produced in
Greenland, situated as suggested over a viscous system of
matter, will act hydrostatically and be felt elsewhere possibly
by elevation in Iceland or Scandinavia ; but as the pressures
will combine with the general system of the polar pressures
in acting upon the heated magma beneath, where this par-
ticular pressure is most reactive at present, that is where
the crust is least resistant, it is impossible to discover except
by observation.
* < Nature/ Sept. 20th, 1883, vol. xxviii. p. 488.
t Lyell's ' Principles of Geology,' vol. ii. p. 196.
PRESENT CONDITIONS CAUSED BY ICE. 197
283. It is desirable perhaps to prevent misunderstanding
to make a slight detour with regard to the sinking of
Greenland, pointing out, what is quite evident, that all
sinking of land cannot be attributed directly to loading such
land with ice, as all sinking surfaces are not so loaded. All
that can be asserted is that accumulations of ice, where suf-
ficient, will cause such sinking. The sinking of a district
may occur through tipping of an area of surface, possibly
through local resistance to polar pressures, which act in the
horizontal direction if this offers less resistance than the
vertical. Such, for instance, as that of the Runn of Cutch,
adjacent to the delta of the Indus, where in 1819 a consider-
able area of land sank in one district and simultaneously
arose in another. Such tipping may also be noticed in the
neighbourhood of volcanic islands where there is contiguous
local elevation. Possibly also in some cases it may be pro-
duced by the loading of the interiors of continents with sand-
drifts produced by prevailing dry winds. The whole of the
instances of depression are small and local, and do not in any
way compare with the numerous great and nearly constant
elevations such as that of the western coast of South
America of from thirty to three hundred feet, for a distance
of 1180 miles along the coast and for an unknown distance
inland *, or that of extensive land-areas in Scandinavia,
which I assume are due to the reaction of accumulation of
ice at the poles upon a deflectible viscous substratum of rocks,
and consider to be a necessary condition, in the present
order of things, to maintain land-areas against the constant
degradation from atmospheric causes.
284. Where Ice-pressures will be most Active. To return
to the accumulation of ice at the poles as affecting by
hydrostatic reaction the assumed semi-liquid interior, and
thereby causing the elevation of land in other parts of the
* Chas. Darwin, ' Geological Observation,' p. 209.
198 NOTES ON THE NEBULAR THEORY.
globe, we may be assured in the first place that such ele-
vation will be subject to two important conditions of the
crust of the earth : 1. The crust may be nearly uniformly
rigid ; 2. The crust may be fractured in parts, or possess
lines of weakness. We will take the first condition.
285. If the crust of the earth is nearly uniformly rigid
throughout its exposed parts, it will be still evident that if
there is an ice-cap of some miles in thickness covering both
the poles of the earth, this ice-cap will materially add to
the rigidity of the parts that it covers ; for we know it is the
property of ice by r'egelation to heal any possible fracture or
strain that may occur from any cause, and thereby constantly
to present a very rigid mass, particularly if it is retained
in a close area or supported by irregular or rigid surface
matter, as before stated. In this respect it possesses a
property of rigidity not shared by the tertiary matter of
the earth, as this remains faulted after it has been once
fractured by an internal strain.
286. If we imagine the ice crust to be maintained at its
surface at an elevation equal to one degree over the Ant-
arctic Circle, that is 24 miles in thickness at the South
Pole, and to be possibly of great thickness at the North Pole,
we may then suppose that the land-surface covered by this
coating will be highly indeflectible* Under these conditions
the greatest effects of the opposing pressures of the poles
would fall more nearly upon the tropical regions, where there
is the greatest surface curvature, and each meridian would
represent as it were a bent bow under the excess of polar
pressure ; therefore in the tropics there would probably occur
the greatest plutonic or volcanic elevation. Now as we
know also that the tropical area, from rainfall, is the area
of most rapid denudation, and consequently of more active
thinning of the crust, we ought also to find evidence of
this being the area of greatest volcanic action, and this upon
the whole is fairly consistent with observation. The following
ICE-PRESSURES. 199
diagram, fig. 23, will give details of the conditions proposed.
Let N and S be the poles covered by an ice-cap, E and W
the equator, TT', T" T"' the tropical regions.
Fig. 23.
We should then expect the surface of the earth or the out-
flow of volcanic lavas from internal pressure to rise to the
greatest height at T to T", T' to T", although this would in
all cases partly depend upon the viscosity and other conditions
of friction within the strata through which the internal
pressures must pass from the region of polar pressures.
287. Taking the above conditions, there are many matters
which at once strike one as relative. Thus the mass of ice
at the poles, placed originally by vapour forces out of equi-
librium with the earth's symmetrical gravitation system as
a spheroid of rotation, exerts a force upon the solid crust of
the globe, which it overcomes in proportion as it is insuf-
ficiently rigid for resistance. In this manner the resistance
becomes distributed, so that it is not only from internal or
hydrostatic pressures, but by direct horizontal pressure upon
the crust that we may have certain facilities of upheaval and
deflection of the surface rocks.
288. Further, if we assume a line of expansion over the
tropical area, which the elevation of lower or interior matter
of the earth and constant denudation really indicates, this
would produce also perpendicular strains in the rigid materials
of the earth's crust, which would follow the meridians, par-
200
NOTES ON THE NEBULAR THEORY.
ticularly in the lines of original polar extension of the
lighter elements of matter ( 250). Thus we should have
brought about the conditions of lines of weakness where the
pressures at the poles would not act in a direction to close
them by any form of crumpling action, as they might be
assumed to do in the latitudinal lines. This principle may be
shown experimentally by the fracture of an india-rubber ball
or a bladder filled with water or air by opposite pressures
towards the centre through one diameter, as shown in fig. 24,
wherein a fracture is produced from n to s.
Fig. 24.
From these causes it is probable that although earthquake
regions exist around the globe as an effect of internal pressure,
we have the greatest volcanic effects in the tropics, other
conditions being equal, which may occur in lines at nearly
right angles to the Equator, and continue poleward over land-
areas as in the South American range.
289. The above cause of fracture, and the lines of weakness
pointed out, may generally rule the positions of volcanic
elevations. But another cause of weakness or faulting
may be suggested, which is particularly relative to the
distribution of ice that is, that in the immediate vicinity of
great accumulations of ice there will be great compression
locally upon the immediate surface strata, and this reacting
with less friction than at a distant part, may cause faulting
near the area of pressure to a considerable depth, as at points
WATER IN VOLCANIC ERUPTIONS. 201
a, a', a", a'", fig. 24. This may possibly account for volcanoes
in the Antarctic and near Arctic regions of Erebus, Terror,
and Skaptar-Jokull.
290. Presence of Water or Steam common to Volcanic
Eruptions. If ice-pressure were present at the poles,
bearing down the surface rocks upon the lower viscous
matrix and causing the displacement of the lower viscous
stratum of tertiary rocks, the originally cooler surface rocks
would necessarily come finally into contact with the central
highly heated metallic core. We may imagine that when
this occurred the surface rocks as they were pressed down-
wards by superimposed weight of ice would be melted at
their lower surfaces, and become themselves heated viscous
rocks. These would be again displaced laterally into the
general viscous mass by the superimposed pressure, until
a thin stratum only of cool mineral matter would remain as
a permanent non-conductor between the ice and the heated
liquid metallic core beneath. The metallic core would also
in time be chilled to a rigid coating by the constant arrival
of cooler tertiary matter abstracting its heat. The weight of
ice at the South Pole would constantly increase, particularly
in antarctic winter, and this must continually react upon the
surrounding viscous matrix beneath, and the surface of the
slightly chilled metallic core, just as the former surface rocks
had previously acted upon it, as there are no possible con-
vection heat currents in the ice. In this case the former
rock-pressure upon the metallic matrix would be replaced by
a water-pressure acting through the thin stratum of rocks,
which must necessarily continue to act as a non-conductor
between the metallic matrix and the ice. Now as we assume
that water as it was liquefied from the ice at the surface
of the lower slowly conducting rock would receive more
pressure above than resistance laterally, it would under-
flow outwards from the sub-polar area and permit more ice
to come in contact with the surface, which would be sufficiently
202
NOTES ON THE NEBULAR THEORY.
heated for its liquefaction, so that the process of liquefaction
and underflow would be continuous for the dispensation of
polar pressures. Further, as the water would underflow
from near the surface of the metallic core in an approximately
horizontal direction, and at the same time be released from
a part of the superimposed pressure in passing beyond the
polar area, its tendency would be to flow upwards through
liquid rocks nearer to the surface, which would be of less
thickness further from the poles. Therefore, convection
currents would be impossible backward to the earlier position
of the melted rocks. In this manner the underflowing water
might become highly heated by the lower semi-liquid rock
through which it flowed. This process may be shown by a
diagram, fig. 25.
291. Let A be the highly heated metallic core of the globe,
the mineral coating of the lower part of which is shown
at x x, x' x" ; Na, Sa' the ice-caps. Then by the pressure
upon the lower surfaces at x and #, the lower liquid heated
matter unable to resist the pressures would be driven to
equilibrium of symmetry with the earth's spheroidal form by
underflowing in the liquid plane x x toward x' x'. Further,
if the ice which formed the caps Na. Sa r by continuity of
pressure penetrated to the surface of a non-conducting
WATEK IN VOLCANIC ERUPTIONS.
203
stratum at x x, where matter was at a white heat within a short
distance from the polar region, it would dissolve and carry
with it mineral matter from the lower surface rocks, which
would be extruded at the first position upon the globe
where it could overcome the resistance of surface rocks to
establish static equilibrium.
Fig. 26.
292. Fig. 26 shows details diagrammatically of the manner
in which water dissolving mineral matter could underflow the
central surface-rocks of the globe. I represents the southern
ice-cap. N the dense metallic nucleus-matter, VR the lower
heated viscous rocks resting upon the nucleus-matter. CR
the present chilled viscous matter forming the surface rocks.
C the chilled surface of the lower viscous matter which serves
as a non-conductor between the heated nucleus-matter and
the ice. L the position where the ice-pressure becomes
sufficient to force the lower water beneath it into the viscous
matter. This occurs at a lateral position where there is the
least resistance to the hydrostatic pressure. The water is
forced to form a channel through the viscous rocks into
which the remaining water below the ice-cap flows. As the
water flows from the polar sub-basin it becomes heated and
204 NOTES ON THE NEBULAR THEORY.
expands possibly to double its former volume and dissolves
mineral matter from the channel it has formed. The aqueous-
mineral matter being of less specific gravity than the viscous
rocks, flows towards the surface of the globe, where it may be
projected as volcanic matter, or by its hydraulic pressure
float up the surface rocks.
The action of release of polar pressures will be generally
paroxysmal, as the channel once opened by the pressure will
continue flowing through backward-pressure until the liquefied
ice beneath the ice-cap is exhausted. The channel will then
close until the hydraulic pressure again overcomes the resist-
tance and causes it again to break through the chilled surface
of the lateral viscous rocks.
A channel originally driven through the viscous rocks
would find ventage near the point of polar pressure, but the
water at the same time would chill the surface-rocks from
which it derived its heat. Under this condition the ventage
would become consecutively lower owing to the surface resist-
ance becoming greater, until, as at the present time, the mass
of chilled matters shown in our diagram at CB prevent the
outflow or projection of the aqueous-mineral matter until it
reaches a great distance from the pole.
The water forced to form a channel in the lower viscous
matter, in becoming heated after a certain length of flow,
would react upon the inflowing current through its expan-
sion as a resistance. In this manner its injection would
become intermittent. I arranged several experiments to show
this and found one that would do so very simply. Making the
stem of an ordinary clay tobacco-pipe red hot, and plunging
it into water, the water enters the tube of the pipe inter-
mittently, and is expanded and projected through the pipe
into the air in separate spirts.
The points of departure for the underflow channels, pro-
jected by sub-glacial pressures from the Antarctic pole, must
occur at the points of greatest extension of land where the
WATER IN VOLCANIC ERUPTIONS. 205
subterranean heat can be best conserved by the more con-
ducting nature of the surface rocks. Two such channels
when they are open leave the Antarctic circle at about 60
W. long, for the South-American range, and about 140 E.
long, for the Sunda Isles. Where the land pressure is not
great near the polar pressure this may continue to be a point
of least resistance where a fault is once opened, as in Mounts
Erebus and Terror in the great Antarctic bay, 170 E. long.,
and cause eruption at this point.
In this manner a volcano would extrude viscous mineral
matter only at its early stages, the backward pressure being
upon liquid rock only ; but assuming that the volcanic crater
continued to represent the point of least resistance to the under-
flow of the system, the continuity of the volcanic outflow
would open out a channel for the following extrusion of water
from the pole, which would carry with it dissolved mineral
matter, or what becomes, when reduced to atmospheric
pressure, volcanic dust and steam. This might finally appear
at such distant points as 6, b 1 , b". To find evidence of the
above stated hypothesis, which I had previously introduced
in a paper read at the Geologists' Association, March 1883 *,
I examined very carefully under the microscope the volcanic
dust that was blown from the Krakatoa eruption in August
1883. I found it to consist principally of very thin spheroidal
surface plates of volcanic glass (bubble plates as I termed them)
of only about 73^0^ inch in thickness, resembling on a small
scale broken watch-glasses. The vesicles, of which the bubble
plates were the remains, were evidently originally filled with
steam from the boiling mineral matter beneath, which expanded
by release of atmospheric pressure, until they burst when cooled
down high in the atmosphere. In this manner they added
the effect of expansion to the polar pressure which propelled
them through the neck of the crater, and therefore projected
* < Nature,' 1883, vol. xxvii. p. 523.
206 NOTES ON THE NEBULAR THEORY.
them to great heights in the atmosphere. The dust I examined
was swept up from the deck of the bark ' Arabella/ sailing
in the Pacific, at 1000 miles east of Krakatoa *.
It is not necessary to discuss the manner in which
heated water at high pressure dissolves rocks in detail.
Water is proved experimentally at a temperature of 412 C.,
and at a pressure of 100 atmospheres, to occupy about four
times its original volume, in which state it dissolves glass
rapidly |- At a higher temperature it dissolves siliceous
rocks, so that this could very well form an underflowing
current of siliceous matter to the volcano, upon the principles
suggested.
293. In all volcanic systems, irrespectively of internal
expansion of projected matter, there must be a tendency, upon
the principles discussed, for the volcanic outflow to rise to
hydrostatic equilibrium with the polar pressure. Thus such
constant open volcanoes as Kilauea may represent safety-
valves of this pressure ; but as this mountain is not so high
as some other volcanoes which have extruded lava recently,
it is quite clear that upon my theory the friction of the under-
current of viscous mineral matter must withhold a part of the
hydrostatic pressure caused by elevation of ice at the South
Pole. This is also evident in the differences of altitude of
Mauna Lao and Kilauea, which are near together.
294. We may conclude that if a volcanic vent rises nearly
to equilibrium with the distant pressure system, the exposed
mass will cool quickly in the atmosphere, and the former
point of least resistance may become the point of greatest
resistance, and the volcano become permanently extinct, or
it may overcome surface resistance nearer the base of the
mountain than the original crater. If the volcano does not
rise to the point of equilibrium it may become intermittently
* Quart. Journ. R. Meteor. Soc. vol. x., July 1884.
t Cagniard de Latour, Ann. de Chimie, ser. 2, xxi. & xxii.
WATER AND STEAM IN VOLCANIC ERUPTIONS. 207
active with others in the same state, each eruption evidently
clogging or preventing by the weight of ejected matter in
the crater future eruptions for a time in the locality, and
making the eruptions thereafter more paroxysmal. If we
omit the friction of the system from consideration, then the
pressure of the highest vertical column of the chimney of a
volcano may be taken to represent the hydrostatic pressure
upon the liquid matrix beneath, and from this the height of
ice at the South Pole might be estimated. For this, Chim-
borazo might be taken. But the evidence just quoted of
Mauna Lao and Kilauea shows that friction may form a large
factor of resistance to the distribution of polar pressures, so
that equilibrium by ventage cannot be estimated.
295. It is impossible within the limits intended for this
work to discuss popular theories with which the above may
at some time come into competition, but it may be well just
to mention the two most popular.
Firstly, that volcanic and plutonic phenomena are due
to the shrinkage of the earth from cooling, which theory
appears to persist in our text-books. This is fully worked
out by the late Mr. Mallet in over one hundred pages of the
Phil. Trans., 1874-5. But the whole matter is built upon
inexact data, and there is such great error in the calculation
that this must in time suppress this weak theory*. Observa-
tions of stratified rocks give evidences almost universally of
vertical separation by open cracks, which indicate quite the
reverse of a horizontal surface pressure, such as would be
the certain result of an internal contraction from loss of
heat, demanded by Mallet's theory to cause the elevation by
crumpling up of the surface rocks. The universal open cracks
are, on the other hand, the natural result of the effect of
elevation by plutonic forces as herein proposed.
Secondly, the theory that volcanic phenomena are pro-
* Appendix B.
208 NOTES ON THE NEBULAR THEORY.
duced by the expansive force of steam, originally proposed
by Spallanzani in 1788, but best known by its development
by Scrope *. This theory could not have been proposed
with a better knowledge of physics. The experiments of
Cagniard de Latour before mentioned, in which water was
made red hot at a temperature of 412 C. with an expansion
of only four times its volume in a hard glass tube without
bursting, demonstrate that water could not act effectively
in the projection of rocks as in volcanic phenomena under
a very moderate pressure of superimposed rocks, say one
hundred feet of liquid basalt, where the water might exist of
a white heat and of not over double its ordinary volume. Of
course, if the rocks were dissolved in white-hot water, as they
would be at this temperature, the water would expand into
steam when the pressure was released by its coming to the
earth's surface ; but this is very different from the assumption
that steam at such pressure is able to cause the elevation
of thousands of feet of solid rock.
296. There is a further condition frequently offered to
support the steam theory in the assumption, in opposition to
hydrostatic laws or the observed conditions of heated rock,
that water may percolate rock at a low level from the ocean
and be projected at a high level where the superimposed
pressure of surface rock is greater, which is evidently
impossible. Neither are deep-seated rocks, as we find them
in deep mines, porous enough to admit of such percolation
even if it were sufficient to account for actual phenomena.
297. The conditions stated in this chapter relate to deposi-
tion of ice since the miocene period. There were possibly
earlier depositions of ice, the conditions of which will be
discussed in the next chapter. But I anticipate that all the
greatest effects of polar compression by ice, and therefore of
volcanic eruption and plutonic action, followed the miocene
* Scrope on Volcanoes, 1825, p. 17.
WATER OR STEAM IN VOLCANIC ERUPTIONS. 209
period, which, I think, from the greater variation of animal life
and its higher development, was a longer period than any
geological epoch that preceded it. This I will discuss later.
Geologists are generally of opinion that volcanic action has
been constant. I am not certain that the evidence is clear on
this point. If a volcanic vent is found penetrating the
silurian surface rocks, there is no reason why it should not be,
in some cases open to observation, a tertiary one, as volcanic
forces penetrate all surface rocks. Neither is it necessary
that igneous matter should reach the surface, as at a certain
pressure it may float up the surface rocks to form mountains
without any extrusion ; and if these are afterwards degraded,
the volcanic vent will appear as though it issued at the
stratum level at which its intrusion occurred. At the same
time there may have been exceptional conditions of ice-
formation at early periods, which will now be considered.
[ 210 ]
CHAPTER XIV.
PERIODIC CONDITIONS OF EARTH-FORMATION PRODUCED BY
EFFECTS INCIDENTAL TO THE NEBULAR CLOUDING AT
INFERIOR PLANETARY FORMATION, AND AT CRITICAL
TEMPERATURES OF MATTER SURROUNDING THE SUN.
298. Condition of the Sun during Earth-formation.
Taking the earth system to have been abandoned by the sun
as a nebulous zone according to the theory of Laplace, the
earliest condition of the sun in relation to this zone would be
that of a luminous globe of nearly the diameter of the earth's
orbit. As the earth-zone commenced to condense and form a
planet, the sun's volume would at the same time be also con-
densing and leaving this zone more free by distance. If
there was any inequality of density in the zone-ring, the
most probable condition, there would then be a separation at
the most attenuated part of this zone, and a further con-
densation in another part by the continuity of the system of
attractions of the denser matter. So that it is probable that
the earth condensed into a nebulous globe by concentration
before any solid matter was formed at its centre.
After the detachment of a nebular planet-zone, this zone
having much greater surface area relatively to volume in
comparison with the voluminous sun, and being open to free
radiation into space in all parts not directly facing the sun,
would condense much more quickly than an equal volume
of the sun's nebula.
299. In considering the condensation of the nebulous zone
THE SUN DURING EARTH-FORMATION. 211
as a special exterior formation, we may conclude that no
condensation could occur unless the radiation of its heat into
space exceeded that derived from the condensing sun, although
at the same time the nebulous zone must have continuously
absorbed the sun's heat falling upon it. Under these con-
ditions the radiation of heat into space from the zone must
have been of its initial amount plus that constantly received
from the solar centre. If we imagine, what is most pro-
bable, that at the early time of condensation by cooling a
clouding would be produced in this zone through excess of
radiation, then the sun's rays absorbed into the zone would
be diffused within it, so that the radiation would take place
from the zone in all directions, but more particularly in the
exterior parts and those perpendicular to the plane of orbit
where it was most open to free space.
300. Under the above-stated conditions we may consider
the effects of the formation of a nebulous planet-forming zone
upon the amount of radiation of heat and light that the sun
would be able to disperse beyond this impediment to an
exterior planet, assumed to be fully formed at the time.
Then, assuming the earth already formed, and the sun
contracting in volume before the period of the formation of
an inner planet, as Venus, a nebular band, or what we may
term the Venus-zone, would appear across the sun's disc,
which would continue to obstruct a large part of his rays, and
this would last until the complete formation of Venus as a
planet. The like would again occur before the complete
formation of Mercury. We have apparently, upon a large
scale, nebulae in this condition *.
After a nebular planet-zone was detached from the sun
its future condensation would depend upon contingent
circumstances.
In fig. 27 the possible appearance of the large nebulous
* 2244 Gen. Cat., Rosso Nebula, p. 90.
212 NOTES ON THE NEBULAR THEORY.
sun is represented partially obscured by the Venus-nebular-
zone at a certain stage of its condensation.
Kg. 27.
301. If Venus or Mercury, from inequality of distribution
of nebular matter after the time when their zone-rings were left
by the sun or from any following disturbing cause, as the
intrusion of a comet, condensed at first into a nebular globe,
as just proposed for the earth ; then this globe, after its
formation, would in time concentrate to an intensely-heated
nucleus at its centre. This nebular system would obstruct
the sun's light through cloudiness at its early period of
formation ; but afterwards for another following period,
when it became incandescent, it would present the same
light- and heat-giving radiation as that of the nebulous sun
to the surface of an exterior planet, or greater in proportion
to its visible surface and its state. This new-formed planet,
as before stated, would therefore be obstructive to light and
heat from the sun if it was nebulous, or auxiliary to it if it was
incandescent. In either case this excess or defect of light
and heat would occur in periods of the newly-formed planet's
synodic revolution in relation to an exterior planet, producing
in either case intermittent periods of intensity of radiation of
light and heat upon the exterior planet.
302. After the periods of the entire condensation of a
newly-formed planet to non- obstructive or non-auxiliary heat-
DISTINCT SOLAR HEATING PERIODS. 213
giving proportions when it could not affect the amount of
heat and light dispersed to an outer planet from the sun, the
sun would return to its normal luminosity according to its
age or state, and become again the only source of heat-energy
to the planet.
303. It is not necessary to assume that the sun, when it was
an immense nebular globe, gave out in its entirety more heat
and light than it does at the present time ; it very probably
may have given out much less at certain periods. The super-
ficial condensation of nebulous matter upon or about its outer
surface would constantly cloud the effects of its intense
internal heat, so that when freed from the clouding influence
of the formation of a planet-zone, it would present to the earth
only the appearance of a magnified image of one of our stellar
nebulae*, or of a large bright cloud.
When the sun's nebular diameter was as great, for instance,
as the diameter of the orbit of Venus, if its surface heat had
been of the same intensity as at present, condensation of
nebulous matter to form the earth would have been impossible.
304. Distinct Solar Heating Periods. Under the conditions
just stated it will be seen that the sun's heating effects as
regards an exterior planet, as, for instance, the earth, would
pass through certain phases or periods from the time of the
formation of one interior planet to that of another more interior.
Thus with regard to the earth we should have one long
period during which the sun would be slowly decreasing in
volume, appearing during this time as a large bright nebulous
globe or stellar nebula. This condition of the sun would
continue, during its condensation, until the time of the dis-
turbing conditions of the clouding effects upon its disc of the
commencement of the formation of the Venus-zone of nebula,
which would, after a time, appear to entirely encircle the
* See 4883 Gen. Cat. Ros. Obs. p. 170, also M81 and tf 1205 Ursaj
Majoris.
214 NOTES ON THE NEBULAR THEORY.
nebulous sun as a dark band. The local condensation
within the nebular band would ultimately form Venus into
a large globular nebulous planet, the clouding-effects of
which when moving over the sun's disc would diminish the
sun's heat in transit and make it therefore intermittent in
intensity with regard to the earth, as just stated, in periods of
584 days. This passing of the nebulous planet over the large
nebulous sun at the time of inferior conjunction might
possibly at first nearly obscure his light and heat, at other
times, exceeding nine tenths of the period of revolution, the
nebular sun would appear bright and open.
305. It will be seen on examining the conditions just pro-
posed, which must be incidental to inferior planet-formation
as regards the earth, that there were nine somewhat distinct
periods of minus and plus solar radiation, therefore of greater
or less heat and light radiation, affecting the formation or
depositions of matter upon the earth's surface. These may
conveniently be defined, to show the effective state of the sun
as a radiating body under the entirely nebular conditions
proposed during the formation of Venus and Mercury as
far as the}^ would affect the earth.
1. Period of open radiation of bright nebulous light and
heat lasting from the separation of the earth-zone from the
sun until the commencement of the condensation of the
Venus-zone, during part of which period the earth was a
nebulous globe.
2. Period of nebulous obscurity of the sun caused by an
absorption band across the sun's disc ; period of dull nebulous
light and heat lasting from the early part of the condensa-
tion of the Venus-zone until its formation as a nebulous
planet.
3. Intermittent light and dull periods of about 584 days,
the bright periods much exceeding the dull periods and in-
creasing in brightness from the time of the condensation of
Venus to a globular nebulous planet until it became non-
DISTINCT SOLAR HEATING PERIODS. 215
obstructive to solar radiation. Period of great disturbance
of local conditions of deposition upon the earth.
4. Period of intermittent excess of bright nebulous light and
heat caused by the presence of Venus as an incandescent
body, particularly near the period of transit, lasting from the
time of condensation of Venus to an incandescent liquid or
solid planet until it ceased to be in any degree auxiliary to
the sun's heat.
5. Second period of bright open light of the sun, lasting till
the commencement of the formation of the Mercury-zone.
6. Period of nebulous obscurity by a dense band across the
sun's disc, lasting from the early part of the condensation of
the Mercury-zone until the complete formation of Mercury
as a nebulous planet.
7. Second period of intermittent light and dull periods of
about 116 days, the bright periods much exceeding the dull
periods, the light increasing with time, lasting from the time
of condensation of Mercury to a nebulous globular planet
until it became non- obstructive to solar radiation. Period of
local disturbance of systematic stratification of disintegrated
matter upon the earth.
8. Second period of auxiliary light and heat, when Mercury
became an incandescent globe, lasting until it ceased to add
to the sun's light and heat. The whole period much less
active than the corresponding period of Venus condensation.
9. Third open period of bright light, lasting from the com-
plete formation of Mercury as a non-auxiliary light-giving
planet until the present period of intense solar radiation and
for all future time of effective solar energy.
306. Influence of Inclination of the Orbits of Inferior Planets
and Eccentricity. It will be seen with regard to the Venus-
zone and the second period of dull nebulous light, that owing
to the inclination of the plane of the orbit of Venus, 3 23',
unless the nebular zone had a sectional diameter of about
10 million miles transverse to this plane, it would not
216 NOTES ON THE NEBULAE THEORY.
continuously cover the centre of the sun's disc, so that it
would appear to shift about from north to south in synodic
periods, the entire variation of which would take about 243
years. This would occur until its condensation into a nebular
globe.
The same conditions as described above would occur in the
sixth period with the Mercury-zone; but in this case we have
an inclination of orbit of 7 with great eccentricity, so that
the centre of the sun's disc would be covered by a nebular
band of 5 millions of miles, and if it were of this diameter
transverse to the plane of orbit, its effects upon the diminished
solar disc would be nearly the same as that of Venus, but in
shorter periods of 7, 13, or 46 years. Under these conditions
the dull periods proposed would be in degree intermittent and
produce great changes in the atmospheric conditions of the
earth.
307. At the formation of a nebulous globe in the early
part of the sixth and seventh intermittent periods, it is pos-
sible that each of the planets Venus and Mercury, when a
nebula, subtended as great an angle at the earth as the nebular
sun of these separate periods. In this manner the sun would
be obscured at every inferior conjunction and have its disc
partly obscured for nearly one tenth of the particular planet's
synodic period. This intermittent condition would probably
produce greater effects upon the earth's atmosphere, and
therefore upon deposition of rocks, than the dull periods,
second and sixth, previously considered.
308. It is scarcely possible to realize the enormous effects
that would be produced by the obscuration of the sun for a few
days only, but very possibly this was only partial. If actual,
nearly the whole of the waters of the vapour-laden atmosphere
would be precipitated. Terrestrial organic life would be
destroyed by the sudden cold. Inland lakes and rivers, and
part of the ocean, would be frozen, so that an entire organic
change in animal life might follow, this being possibly
EFFECTS OF FORMATION OF INFERIOR PLANETS. 217
afterwards evolved from the preservation of former marine
and aquatic species that could retain life only by remaining
deep in the ocean. So that, so far as this proposition goes,
evolved species may not be found to be by any means
uniformly progressive from the highest types throughout
geological time, that is, even for the known progressive types.
309. In the above scheme we have considered the effect of
the condensations of Venus and Mercury, which were possibly
largely induced by the reduction to the critical temperature
of the nebular matter which formed the central solar system,
95. It is probable that this formed only a part of the
changes in the amount of heat radiated from the central solar
system to the earth. The conditions of critical temperature
of the sun have been discussed. The condensation which was
capable of detaching a planet-zone would at the same time, as
before proposed, obscure a large part of the heat of the central
system by metallic cloud. Further, the extensive critical
condensations which would form a planet-zone would be ex-
ceptional. There were most probably many minor conden-
sations at the critical temperature of certain elements which
produced no detachments from the central solar system, but
only partially obscured his light and heat. This would cer-
tainly occur within the long period following the condensation
of Mercury. Possibly such a condensation may have pro-
duced our glacial period. Even at the present time the sun's
radiation may vary greatly in long periods depending upon
the sun's surface density, that is, the amount of condensation
at critical temperature tending to cloud the chromosphere.
Under any condition the interval period of open solar radiation
caused by the simple contraction of the sun's volume when no
effects of planet-formation were present would, in all proba-
bility, exist for a much longer period than that of any planet-
formation. This will be reconsidered. It is only important
now to recognize the general effect of the contraction of the
sun upon the earth in its more extended action.
218 NOTES ON THE NEBULAR THEORY.
310. General Effects of the large Nebulous Sun upon the
Earth's Meteorological Condition. Perhaps the most distinctly
important condition that would be due to a large nebular sun,
free from the disturbing effects of planetary formation, would
be that the whole of the earth might be diurnally lighted and
heated by the sun, and that this diffusion of light and heat
would establish very calm conditions in the atmosphere.
The tropics would not be excessively heated and the polar
regions would receive at all times direct sun's rays, so that,
assuming the body of the earth had cooled below a temperature
to affect the evaporation of the oceanic surface, there would
not be the excess of evaporation and expansion of air and
vapour over the tropics as at present, due to solar radiation, or
the great excess of condensation in polar areas, to produce
the violent atmospheric currents we have at present in
storms and cyclones.
311. At the period when the sun had condensed to the
orbit of Venus, the diameter of his disc would exceed 67, so
that it would present a luminous surface of this angle, and
the poles, even in mid-winter, would have a segment of the
sun shining daily through an arc of 10 versed sine. At the
period when the sun had decreased to the dimensions of the
orbit of Mercury it would still present an angle of 44. There-
fore, even in mid-winter, there would be at least a daily twilight.
Altogether the general conditions of the globe would be very
equable as compared with the present, although, of course, the
polar area would still be colder, as being more open to free
radiation. If, on the other hand, we consider in contrast the
conditions that would be active during the shorter intermittent
periods 2, 3, 4, 6, 7, and 8, 305, the atmosphere would at
these times be subject to constant disturbance by high winds
and heavy rains in intermittent hot and cold periods, which
would cause rapid decomposition of rocks, and generally
produce intermittent thin planes of varied stratification.
312. As regards depositions of matter upon the earth from
EFFECTS OF LARGE NEBULOUS SUN. 219
degradation of rocks, these must depend always in amount upon
the atmospheric conditions present. We might have a long
period during which depositions went on very slowly. A
period of light rains and nearly constant sunshine, in which
very little matter would be detached from the rocks or
brought down to the sea-level, during which time, the con-
ditions of life being constant, there would be very little reason
for any change of form, and the strata of universal matter
deposited, although uniform, would be very incommensurate
with the time. On the other hand, we might have periods of
heavy rainfall and frost in high lands, during which time de-
gradation and deposition would be very rapid and the strata
formed be very deep for the limited time of formation. With
great change of atmospheric conditions there would be great
struggles for existence, in which favourable varieties of life-
forms only would survive.
So that, on the whole, no depth of geological stratification
nor even changes of animal life will indicate, with any exact-
ness, the extent of time of a geological period unless we possess
other data for consideration.
[ 220 ]
CHAPTER XV.
CONSIDERATION OF TIME ELEMENTS IN THE SOLAR SYSTEM,
PARTICULARLY FOR ESTIMATING THE AGE OF THE EARTH
AND FOR ITS GEOLOGICAL PERIODS.
313. Time of Condensation of our Solar System. This may
possibly be found with some degree of approximation by
estimating the rate of contraction of the original nebula upon
thermodynamic principles. For this calculation we may
take the dimensions of the nebula at any period of its con-
traction when it occupied a space within the extent of our
solar-planetary system until the present time, when it has
contracted to the small volume of our sun. In this propo-
sition we again accept the probability that the nebula was
originally one of the symmetrical planetary nebulae of which
we possess many instances open to astronomical observation.
A probable form being that of one of the nebulae shown,
Plate II. a, 6, c, or d. Such a nebula under the conditions
we have assumed throughout this work, must have condensed
constantly by radiation of heat from its surface, and at the same
time have formed our sun by concentration of matter about
the centre. We may form an estimate of the extent of this
nebula, at least at a certain period, by the extent of the
extreme planetary orbits of our system ; and if we knew the
rate of radiation at the surface and of concentration of matter
at the centre or sun as a heat focus, we could then estimate
the time the system may have taken to arrive at its present
state.
TIME OF CONDENSATION OF SOLAR SYSTEM. 221
314. If we omit the consideration of the reaction of con-
densation of heat in the central nebula or sun, and regard
the radiation as a superficial function only, this will dispense
the mean energy of the system in proportion to the tem-
perature and extent of surface. If we assume that the
heat was equally distributed throughout the volume of the
nebula, the surface-heat would be nearly maintained by the
superficial contraction and by heat exchanges with the
interior of the system. Taken in this manner, a voluminous
nebula would condense to less depth superficially in a given
time than one of smaller volume.
315. Observations of planetary nebulae, as, for instance,
$ I. 205 or M 81 Ursse Majoris, Plate II. b and d, show a
central condensation of large volume surrounded by a more
attenuated medium. Under this condition, which we have
assumed throughout this treatise may represent an early
stage of our solar system, we have necessarily two distinct
systems of condensation that about the solar centre which
condenses its matter from the more attenuated surrounding
medium, and that at the surface of the medium itself, which is
contracting in space. The final condition of such contractions
we assume will form a sun or star, that is, a unit incandescent
mass. We may assume that our sun has arrived at nearly
its final state. The only representative of the former nebular
state being found in the chromosphere, and the largely diffused
surrounding matter of which we have evidence in the corona
and the zodiacal light.
316. The amount of condensation of the surrounding
luminous matter or pneuma into the central solar nebula
cannot be defined ; but as the condensation must have pro-
duced heat at the surface of the interior nebula, which again
reacted by radiation, it is not probable that the interior con-
traction was greater at any time than it is at present. For in
the first case, the solar contraction would be blanketed by
the surrounding pneuma, and in the present state its heat is
222 NOTES ON THE NEBULAR THEORY.
freely dispensed into open space. Therefore we may con-
veniently consider the present contraction of the sun as a
periodical constant without great risk of error, for which we
may obtain some data from thermodynamic laws. On the
other hand, the contraction of the attenuated medium or
pneuma, which formed the limiting volume, as this has
practically disappeared from the solar system, must have
proceeded at a higher rate. For this calculation we may
indulge in certain assumptions which may give approximate
results.
317. According to the original calculation of Helmholtz the
sun's radius is diminishing at the present time by 1/10,000 part
in 2000 years =1/20,000,000, or 126*32 feet annually. This
estimate has since been slightly increased. For an even
number we will take 130 feet, which for convenience may be
considered as a constant of time-condensation of the solar or
nucleus nebula from the early period which we are now
considering.
318. As regards the limiting superficial contraction of the
pneuma, we will suppose that it condensed in some degree
in proportion to its tenuity or distance from the solar centre.
At a distant position it may have been rapid ; on the sun at
present it may have nearly ceased. We will take it that at the
period when the solar nebula extended to the orbit of Neptune
the mean annual decrease of its radius was, as an extreme
condition, possibly equal to two miles. Upon these data
time elements may be calculated.
319. For the time of condensation of the solar nebula to
the present condition of our sun we will call the radius or
mean distance of the orbit of Neptune, in feet, r ; the
radial contraction of the solar nebula equal to two miles, or
10,560 feet,/; and the constant of central solar contraction
S = 130 feet. It is then clear that / diminishes, as it is
assumed to do, at a uniform rate until it has vanished at the
present time, its mean diminution was half this rate. There-
TIME OF CONDENSATION OF SOLAR SYSTEM. 223
fore the mean total diminution of the nebula for the limit of
nebular condensation from the period will be *!+> This
i
divided into r gives "7 =, time; which we find to be 2723
millions of years the suggested time of condensation of
the solar nebula from the dimensions of the orbit of Neptune
to those of our present sun.
320. Taking the same formula for the earth, calling its
orbit-radius or distance from the sun r', or about -fa of r, we
have 7 - =t f , which gives t' (earth-time) about 1008 millions
of years, or, roughly, 1000 millions of years, for the time of
the condensation of the solar nebula from the earth's orbit
until the present time.
321. The above calculation may be taken as quite the
inferior limit of time ; no allowance has been made for the
condensation at the solar focus which ultimately formed our
present sun, which might increase in volume directly as the
increase of gravitation from nearness of the more refractory
matter to this centre, possibly in inverse proportion to the
distances of all parts of the nebulous matter from the centre.
The increasing compression of matter about the centre would
more perfectly conserve the heat of the system, surrounded,
as it would be, by a denser nebular atmosphere according
to Lane's law, 11, p. 11. Therefore it is not probable
that the decrease of volume from the effects of outer surface
radiation of the nebula would progress at quite so high a
rate as that just stated.
We will now consider the conditions of time-variations of
heat and light from the sun during its condensation, from the
period when we assume it to have been a nebulous spheroid of
the radius of the earth's orbit until the present time.
322. Distribution of Time upon the Earth throughout the
224 NOTES ON THE NEBULAR THEORY.
varying periods of the Condensation of the Sun and the Inferior
Planets. This may be taken from the calculation just given
of 1000 millions of years, making the divisions of time by
fixing certain radii of the nebulous sun, to correspond with
periods previously defined, for the probable clouding and
auxiliary effects upon the sun's exterior radiation during
planetary formation. In this proposition we may possibly
divide the period of radiant energy into four classes con-
sistent with our table. We may take solar energy to be
open to be obstructed to be intermittently obstructed and
open or to be increased by the energy of the condensed
planet when this was in an incandescent state. The duration
of these periods was probably proportional to the rate of
condensation. I will take as hypothesis the formation of the
nebular zone of Venus to have been obstructive to solar
radiation during the sun's contraction for one fourth of the
distance between the orbits of the earth and of Venus. That as
soon as the sun's nebula was quite free from the Venus-zone,
Venus would commence to form a nebulous globe. We will
suppose that this nebulous globe remained intermittently
obstructive to the sun's rays until the sun had contracted to
one eighth the distance between the orbits of Venus and of
Mercury. That Venus then gradually contracted and became
by incandescence a bright body of possibly not more than
six times its present radius. At this time it would be com-
parable with the sun in density, and probably for a short
period much brighter than the nebulous sun, even possibly
as bright as our present sun. This state of Venus would
slowly cool down, and possibly when the sun had contracted
to one fourth the distance between the orbits of Venus and
Mercury, Venus had ceased to become in any measurable
degree a heat- and light-giving factor to the earth. After
the condensation of Venus as a cool planet shrinking to
nearly its present dimensions, the sun would remain open until
the condensation to form Mercury. Mercury would then go
TIME OF CONDENSATION OF THE SUN.
225
through changes similar to those of Venus in proportion to its
mass and its distance from the sun.
323. Taking the above-stated condition that the contraction
of the sun's nebular radius remained proportional to the time
of condensation, we may construct a table for which we take
1000 millions of years, previously given, as the entire interval
between the earth's separation from the solar nebula until
the present time.
TABLE.
Conditions of the Nebulous Sun at its radius in Millions of
Miles for nine Periods in Millions of Years.
Period.
Radius of sun
in million miles.
Difference.
Time in
million years.
1. Open
93 to 73
20
114
2. Dull
73 to 67
6
40
3. Open and Dull
67 to 63
4
26
63 to 60
3
14
5 Open
60 to 37
23
197
6. Dull
37 to 33
4
41
7. Open to Dull
33 to 31
2
22
8. Auxiliary
31 to 30
1
14
9 Open
30 to present
30
532
This table may possibly continue nearly proportional if we
consider the specific heat of the solar nebula less and its
radiation greater, or vice versa factors that cannot be exactly
estimated.
324. Period of the Formation of the Nebulous Earth. If
we take the period from the separation of the earth-zone, as
proposed, 298, and assume this nebular zone was ten
millions of miles in cross-section of the annulus, this would
give upon condensation, if all its parts moved with equal
angular velocity, an excess of rotation to the condensed globe
produced therefrom over the revolution of the moon and
Q
226 NOTES ON THE NEBULAR THEORY.
the rotation of the earth at the present time ( 146) ; but
as we presume that this zone would be partially condensed to
discrete matter from exterior matter drifting in spiral paths
thereto (222), which in falling upon the earth would tend to
cause a negative rotation, the cross-section of the zone-ring
proposed above may not be too great. This zone after
detachment could not maintain its heat to the extent
formerly suggested for the surface of the nebulous sun, as we
have no large intense centralized source of internal heat
comparable with that of the sun within the zone-ring, so that
its heat would depend upon its condensation only, and,
as this zone would possess much larger surface, relatively to
volume, than the sun, it would be open more freely to radiation
and contract at certainly quite double the rate of the sun.
This would, as before stated, occur principally at its outer
surface away from the sun, and at all outward angles trans-
verse to the plane of orbit, as no central heat from the sun
could fall upon these parts. In this manner the trans-
verse radiation of heat from the zone would make the total
contraction of the zone proportional to its sectional radius.
Upon this proposition taking the sun's nebulous contraction
at the position of the orbit of the earth as before proposed
f
= ~ + S, which will be 482 feet in a year, or at the position
o
of the outer surface of the ring about 500 feet in a year,
denoting this by a, the number of miles in the ring-section
by 6, the number of feet to a mile by c, and dividing by 2 for
the contraction of opposite sides of the ring and again by 2 to
be
make the contraction double of the sun's, we have - or
10,000,000x5280
=26,400,000 years, for the period of con-
traction of the earth's nebulous zone upon itself to the position
of the axis of the ring.
325. In the above-stated proposition the contraction of the
FORMATION OF THE NEBULOUS EARTH. 227
earth's zone-ring upon itself can only be considered theoreti-
cally as the modus operandi. To give the moon its revolution
period and the earth its rotation, we must imagine a separa-
tion to have occurred at some part of the nebular zone, under
which condition, simultaneously with the contraction of the
section of the ring, it was being drawn together by gravita-
tion acting in the linear direction of its circumference so as
to form a nebular globe. This would, of course, materially
complicate the conditions of the calculation of time by
a differentiation difficult to follow ; but as the radiation-
surface would certainly be constantly lessened during the time
of globular condensation, we may prolong the time possible
by nearly double the amount of the time suggested, say, to
50 millions of years, for the condensation of our earth from
a nebulous zone to a liquid globe at an intense white heat,
surrounded as it must necessarily have been by an extensive
nebulous atmosphere. This globe would possibly be formed
principally of iron with the presence of other highly refractory
metals, and become the permanent nucleus of much the greater
part of the volume of our present earth, upon which the
deposition of oxidized matter may have been superimposed
upon principles already discussed. The superficial conditions
are represented by the geological periods of the earth, to be
considered in the following chapter.
Q2
[ 228 ]
CHAPTER XVI.
GEOLOGICAL PERIODS CORRELATED WITH ASTRONOMICAL
PHENOMENA.
326. Geological Periods. Leaving out of consideration
any notice of the early paroxysmal school of geology, the
eminent geologists, among whom Murchison, Sedgwick, and
Miller may be particularly distinguished, who have made
attentive study of a single group of ancient rocks, have
come to the general conclusion that there have been special
periods in the past which have been conducive to the formation
of special kinds of rocks, which, with the fossils therein con-
tained, are very distinguishable from other periods. That in
and during the different periods for an immensity of time,
wide areas of the globe were affected by like conditions from
causes unknown. So that if we take, for instance, as the
most striking example, the Silurian period of Murchison, this
appears to be characterized by the presence of finely-deposited
rocks in an entire broad band of unequal thickness surrounding
the Northern Hemisphere, containing fossils of a similar
succession of faunas, marked by particular zones of genera
and species. It is probable also, judging from rock-texture
and organic remains, that similar general conditions affected
the land-areas of the Southern Hemisphere during the same
lengthened period.
A school of thought, founded by the genius of Hutton and
developed by Lyell, wherein due recognition, not previously
taken, is made of contemporary formations, has arrived at
GEOLOGICAL PERIODS. 229
the conclusion that the present agents at work would, if
active in the past, account for all former conditions of
deposition. The theory hidden in the argument offered appears
to be that of the improbability of other changes being active
upon the earth than those due to successive astronomical
and physical conditions, which are still active, and to the
differences of position of land and oceanic areas upon the
globe.
327. Quite outside all theoretical induction is the work of
the practical or field geologist, who accumulates facts derived
from observation irrespective of theory, and makes through
observation only a broad distinction between the more
ancient rocks, which were in a wide expanse special and
uniform per stratum, and the modern rocks such as are at
present forming, which, excepting possibly in the deeper
part of the ocean, are locally only in very narrow limits
similar to each other and vary in character in separate locali-
ties in every degree. So that, taking the mean of geological
opinion upon the early conditions, there appears -to be the
extreme probability of the action of conditions in the cosmic
system which have entirely passed away. These I propose
now to consider as the effects of the astronomical changes
already proposed in previous pages which have remained
more or less evident in the early stratified rocks.
328. It will not be found practicable in this .essay to con-
sider stratification of rocks in detail. This has been well done
by many scientific specialists in our advanced elementary
treatises on geology, of whom it is only necessary to mention
such names as Lyell, Dana, Geikie, Le Conte, and Dawson.
It will therefore be necessary to consider in what follows
the system of forces already proposed, which were probably
active on a large scale as prime movers throughout the distant
past under certain special conditions. There must also at the
same time have been conditions which were constantly active
affecting the deposition of mineral matter upon the earth.
230 NOTES ON THE NEBULAR THEORY.
Of this may be mentioned the constant decrement of the
sun's volume, the condensations of the solar- nebular, matter
at critical temperatures, the astronomical constants of variation,
of eccentricity of orbit, precession of the equinoxes, and change
of obliquity of axis, and possibly also some changes due to the
revolution of the magnetic pole which have not yet been
recognized.
329. By a general consensus of geological opinion the
conclusion is arrived at that the long periods of deposition of
surface-rocks which are open to observation can but be
representations of detached units of geological time. This is
shown most clearly in the great changes of animal remains
between one stratum or set of strata and the next, in which
the lost period of evolution often appears to be much
greater than the long period made evident by the slow
deposition of a formation or indeed sometimes of a single
stratum. That this should be so may be inferred from
the slow but constant action of meteorological forces alone
in disintegrating rocks, which must always have been
active upon the rocks protruded above the oceanic surface,
and have produced continuous contiguous deposition of
these rocks in another form at a lower level. This deposi-
tion, which is general over the floor of the ocean, does
not necessarily at any period become visible as surface-rock
unless it is elevated by plutonic forces above the level of
the oceanic surface. The evidences of the fossil and other
remains in the rocks, which remain permanent as it were
by the accident of being projected above oceanic level, show
in many cases that our visible surface-rocks may have been
elevated locally by plutonic forces and have been degraded
by meteoric forces many times before they produced any of
the present finely disintegrated strata. The materials of the
rocks appear after disintegration to be sorted out as it were,
so as to depart entirely in structure from their original
character, and therefore they must lose their former history.
GEOLOGICAL PERIODS. 231
The whole vestiges that remain of the long periods of the
geological past represented by detached units, generally of slow
deposition of mineral matter brought down by the action of rain,
snow, wind, and tides, together with the large accumulation
of remains of animal and vegetable life that have escaped
after degradation, amount altogether to some 18 to 20 miles
in thickness of deposition only, and these in separate detached
units are all we possess from which to draw any inference
whatever of the long period of past geological time.
330- The above statement, as regards the extent of past
geological time in its entirety, does not preclude our recog-
nition, if we please to accept it, of the evidences of certain
conditions that ruled for certain long periods for which we
may attribute active causes. Thus, as an instance, during the
great Silurian period before mentioned, we find locally even
miles in thickness of finely and slowly-deposited rocks in
even stratification in a system which appears to have extended
to a greater or less depth over the larger part of the Northern
Hemisphere. In this we find here and there ripple-marked
surfaces left of the ancient quiescent oceans, and of rain-
marks on the smooth sandy beaches of the period. We are,
therefore, upon these premises bound to conclude that during
this time we have a period of mild quiescent atmospheric
conditions and of the minimum effect of tidal action, possibly
with heavy rainfall, for which causes may be fairly suggested.
This subject will now be considered generally by taking the
separate early periods defined by modern geologists and
endeavouring to correlate them with the periodic conditions
which have been proposed, particularly with regard to the
action of the effective radiation of the sun's heat and of his
contemporary volume under circumstances which have been
already discussed.
331. Archcean Period. After the metallic nucleus of the
earth was formed ( 235), we should have the possible approach
of lighter nebular matter and its union with the surrounding
232 NOTES ON THE NEBULAR THEORY.
oxygen and halogens present, entailing complicated chemical
processes, the principal factors of which would be the con-
densation and deposition of oxides and haloids upon the
cooler polar areas of the earth, as before, proposed. The great
atmospheric pressure would cause also the heavy rains of
highly heated water in circumpolar areas as before stated.
The hot rains under the great pressure would dissolve the
siliceous, aluminous, and calcareous rocks that were already
precipitated from the condensed nebula near the poles and
those also that were crowding outwards in pressure-folds
under the influence of gravitation whilst floating upon the
central dense liquid metallic base-matter. By the hot rains
the protruding rocks as they were constantly dissolved at
their surfaces would be brought down into the hollows.
332. Afterwards, as the atmosphere cooled, the semi-liquid
rocks would be gradually deposited in a crystalline form in
hollows and lake-basins. These depositions from aqueous
solution probably produced the foliated crystalline rocks of
the period most largely in gneiss, but partially also in mica
and hornblende schists, chlorite slate, and crystalline lime-
stone.
333. The land-areas formed of newly-deposited rocks at
the close of the Archsean period would be left elevated by
outward pressure of plutonic forces through polar pressures
to great height at a distance around the poles. These rocks
being constantly overflown with hot water left a system of
permanent rocks, as before stated, locally thrown up at any
point of minor resistance upon the first thin crust of the earth,
or retained at the lower levels deposited from solution from
its saturated mineral waters. The constant outflow of the
lower heated viscid rocks moving into equilibrium to gravita-
tional position, caused the upheavals from resistance to take
place more particularly at the rounded borders of continental
lands, from causes already pointed out. The general land-
surface, therefore, was thereby covered with lake-basins formed
GEOLOGICAL PERIODS. 233
by surrounding mountains most elevated at the polar sides.
These basins as the temperature lowered held the deposits of
mineral matter brought down by the hot rains, particularly
from the poleward slopes, where rainfall would be heaviest.
334. The entire system of what we now term the Archaean
rocks is here assumed to be of the primitive rocks, which
formed by themselves, and by after-degradation and ultimate
deposition, the entire surface-rocks of the globe, as there
could be no further deposition of mineral matter after the
deposition of oxides and haloids from the nebulous atmosphere.
This system of rocks, including the deepest or lowest stratum,
which still probably retains a white heat, could not have been
less than 100 miles in thickness. The chilled surface-rocks
of the Archaean system, left measurable at the present time in
Canada, the Outer Hebrides, Bohemia and Bavaria measure
about 40,000 feet in thickness.
335. Archaean Time in relation to the Conditions of Animal
Life. As the lower or early-deposited basic rocks not exposed
to surface-radiation would remain for a long period in a hot
viscous state, they would continue to flow slowly to a position
of gravitation-equilibrium, distorting and crowding up all
the new cooler incipiently-formed strata. It is during this
period, which would have extended until the commencement
of the clouding effects produced by the condensation of the
nebular zone of Venus, that I propose to place the complete
formation of our recognizable Archaean rocks. This period
possibly lasted altogether from that following the liquid
condensation of the metallic core of our globe for about
84 millions of years. This would complete nearly the entire
first bright period, during which time the earth would
remain in too highly heated a condition to maintain life upon
its surface. Most probably during the latter part of this
period, perhaps for 30 millions of years or longer, completing
the 114 millions of the first period of our table (p. 225),
the polar regions may have decreased in temperature by the
234 NOTES ON THE NEBULAR THEORY.
excess of polar radiation cooling the superincumbent vapour
into rain-clouds of sufficiently low temperature upon precipi-
tation to allow the commencement of organic life in polar
regions. This new life, the cause of the beginning of which
must rest in the Great Unknown, would be afterwards slowly
distributed in succession further and further from the poles
as the latitude-temperature fell by the continuous secular
cooling at greater distance therefrom. The distribution
under changes of circumstances would cause local variation
of species outwards from the pole for adaptability to the
surface-conditions ; but as life- variation is a very slow process
there would still be strong affinities in the newer animal life
as it extended, with that which preceded its departure from its
primitive polar home.
336. The Archaean rocks are here taken to be the earliest
chilled superficial rocks, for the greater part projected to the
surface by plutonic forces and acted upon by the ruling con-
ditions present ; but if we consider that the same forces are
still evidently active to a certain extent in producing plutonic
and volcanic phenomena, we can but take it that the system
is more or less a continuous one lasting until the present time.
The outward form of these rocks, particularly the mode of
crystallization, must certainly vary in time from the differences
of surface-conditions of the globe, in the heat maintained at
the surface, the pressure of the atmosphere, the amount of
aqueous vapour, and the mass of such elements projected to
or beneath the surface at any period ; but the materials must
vary very little in chemical composition, coming, as they are
here suggested to do, from the same universal source of
exterior nebular deposition.
337. As we leave the Archsean period, we have new lights
breaking upon us to guide us to the evidences of past time
shown in the somewhat systematic evolution of organic life.
But in this we have to contend with a constant erasure of
evidences through the activity of the atmospheric phenomena
GEOLOGICAL PERIODS. 235
within any period, as before stated, which may leave us but
faint indices of the changes through which the life and
materials of surface-rocks may have passed before the rocks
that remain to observation were formed. Thus in the 40,000
feet or so of old Cambrian and Silurian rocks to be presently
considered, there is little evidence that we can derive from our
experience of rock degradation and deposition that these rocks
were formed directly from Archaean rocks. Indeed we must
almost conclude from the average fine structure of the Silurians
that they may have been churned up by atmospheric forces very
many times during the Archaean period before they arrived at
the state in which we find them in the Silurians. What we
appear to possess indices of in rock-texture in many cases,
is that there were within the Archaean period some special
periods of deposition, separated possibly by longer periods,
wherein rocks were deposited and disintegrated many times
before they formed the strata we find open to observation which
may have been formed by a special local deposition at a certain
period. It is also probable that these periods of deposition
were apart from any uniform conditions and depended greatly
upon certain special conditions that were active upon the
globe from the astronomical causes already discussed.
338. Cambro-Silurian Period. Long before the condensa-
tion of the Venus-zone previously described, nebulous matter
condensed interior to the earth's orbit would be floating in
spiral bands towards this zone, sunward, obscuring a large
part of the light and heat of the then large nebulous sun,
so that the obscuration caused by the condensation of the
Yenus-zone when it was abandoned by the sun might not be
very sudden ; but as this zone cooled, the obscurity would
constantly increase up to a certain point of its condensation,
possibly even so far cooling the earth as to produce a tem-
porary glacial period about the poles.
339. At the commencement of the formation of the Yenus-
zone, the vapour-laden atmosphere would exert a pressure
236 NOTES ON THE NEBULAR THEORY.
much greater than the present. The heavy temperate rains
that fell at first over the polar areas only, would gradually
extend over the present temperate regions, by which the
surface-rocks would be worn off and washed down to the sea-
shores, and pelagic life spreading originally from the poles
would inhabit these temperate shores. The shores, by the
excessive rainfall would be again covered with new deposits,
brought down from the still elevated Archaean rocks, in which
the mineral remains of organic life would be buried until
the sea-bottom extended outward to a great area from the
coast. These deposits would be again further diffused by
oceanic currents. The sea would constantly but slowly rise
by the amount of deposition in proportion to the inland
denudation, and in a small degree by the loss of vapour in the
atmosphere, and overflow its former boundaries.
340. The polar regions, by the effect of constant rainfall,
would become degraded, as they would be also falling in
temperature through the obscurity of the sun, until in pro-
cess of time the cold would be sufficient at the most obscure
period to cause life to become extinct through wide circum-
polar regions. At the same time, under diminished heat from
the sun, marine life, spreading outwards over the then tem-
perate latitudes from the polar regions, would be supported by
convection currents from the warmer submarine rocks not
yet cooled to surface-temperature, so that life would extend
over the entire temperate and tropical regions of the
globe.
341. In the most obscure part of the period the initial heat
of the globe, superficially cooled down, would maintain the deep
waters in the tropical and temperate latitudes upon its surface
at a fairly equable temperature favourable to marine life.
Although under these conditions, if by ebb of tides or other
circumstances such marine life was exposed in restricted areas
in circumpolar regions without the circulation of warm
currents, it would be destroyed by the low temperature
GEOLOGICAL PERIODS. 237
from the little heat given by the obscure sun, particularly in
the winter solstice.
Towards the time of extreme obscurity of the Venus-zone,
copious snowfalls would occur over the polar regions, which
would press upon the chilled surface with sufficient weight to
react upon the still semi-fluid siliceous rocks immediately
underlying the surface-strata, so that these rocks might be
pressed outwards in under-currents and underflow the surface-
rocks, causing extensive local and mountainous elevations over
many regions. These lower heated rocks would also overflow
the earlier rocks in some districts by exudation due to reaction
of polar pressures. *it**-
342. I place the duration of the Cambrians and Silurians,
some time antecedent to and throughout the first dull period
given in our table, p. 225, during which time the earth
was sufficiently cooled down to permit the spread of marine
life, at 96 millions of years according to our scale. This period
to the field-geologist may appear relatively short to represent
the great extent of deposition, which is locally in some districts
40,000 feet or more. We must, however, in this case consider
the active state of the atmospheric conditions present, which
would produce a nearly constant rainfall over a large part of
the globe, and therefore that it was a period of constant
deposition.
343. We have further the probability that the subaqueous
equatorial regions of the earth continued sufficiently heated
near the solid surface through all this period to produce a
constant copious evaporation of the equatorial oceans, so
that from this cause again the temperate regions would receive
excessive rainfall, which would flow down to the warm oceans
carrying mineral matter. The time, again, appears short for
the evolution of the great quantity and variety of organic
remains of pelagic life that we find in this period. But here,
again, we have the probability of life having originated much
earlier over the cooler polar regions in later Archaean times,
238 NOTES ON THE NEBULAR THEORY.
as before stated, 153, and the possibility at this time, from
the large disc of the dull nebulous sun subtending an angle,
as proposed, of 67 degrees, that the small amount of heat
derived from the sun was so distributed over temperate
regions that it was particularly conducive to the rapid spread
of marine life in the constantly subaqueously-warmed seas.
In fact it was, as the fossil remains indicate, a perfectly
equable quiescent temperate time, although under very
constant rainfall except only that the polar regions in the
most obscure time may have been deeply covered with snow
and ice, as before stated, to produce about these regions a
temporary glacial period with contemporary elevation of
surface-rocks elsewhere upon principles already discussed.
Daring the publication of this work it has come to my notice
that the equable condition of Silurian time, as being due to a
large nebulous sun, has been suggested by M. C. Wolf in his
able work ' Les Hypotheses Cosmogoniques,' p. 32.
344. The general evidences of the Cambro-Silurian time
indicate that comparatively shallow seas prevailed or extensive
flat shores which abounded with life. The frail shells indicate
quiescent oceans free from storms and from much tidal action.
These shores were constantly thickened by new deposition of
fine sands, mud, or calcareous concretions, consequently to
remain shallow they must have sunk or the ocean must have
risen. Most probably both these conditions occurred. The
recently highly-heated rocks would be slowly shrinking by
loss of heat in superficial strata ; and at the same time in
this early age there would be a slow underflow of the still
viscid lower heated rocks that were moving equator-ward to
gravitation-equilibrium. At the same time the excess of
rainfall would be lowering the surface-rocks, and in this degree
raising the oceanic level as before stated, the whole condition
causing great depths of shore deposits. The ripple-marks
which give the evidences of quiescent times, independently
of the even stratification, were possibly preserved to us by
GEOLOGICAL PERIODS. 239
occasional light clouds of dry dust blown over them from
the higher lands during summer.
345. Devonian Period. When the nebular zone of Venus
had become broken and had commenced to condense to a
nebulous planet of large diameter its disc would alternately
obscure the sun and leave it open. At such a time the
intensity of the heat and light of the sun would be inter-
mittent in periods of the synodic inferior conjunctions of
Venus. Such intermittent periods, by causing periodically
rapid changes of temperature from mild to intense cold,
would render the land-surface incapable of maintaining
either vegetable or animal life, and be also destructive of
littoral mollusk life. But in the open ocean, where such
atmospheric changes due to temperature would create great
disturbance, and thereby increase of the oceanic circulation,
deep-sea mollusks and fishes of migratory habit could
survive. It is at this period we have possibly the early
progressive evolution of distinctly vertebrate fishes, which
appear to be in a certain degree allied to the later forms of
crustaceans and to the embryo forms of the future reptiles
possibly evolved partly, I would suggest, by extension of the
caudal parts of these early animals, so that certain early
crustaceans represent the head only of the later fishes. These
fishes, which came to perfect development in the period
represented by the Old Red Sandstone in Great Britain, were
evidently forms adapted to the required conditions of migratory
habit. They possessed in most cases powerful fins and tails,
the fins in some cases being possibly adapted to rapid
surface swimming, such fishes of the entire family of the
Asterolepidse, as Coccosteus dedpiens, Pterichthys ollongus,
Cephalaspis Lyelli. Other fishes were evidently adapted to
deep-sea swimming, as Holoptychius nobilissimus, Osteolepis
major, and many other forms, all of which were equally
adapted to migratory life.
346. After the intermittent obscure period there would be
240 NOTES ON THE NEBULAR THEORY.
a period in which the condensing globe of Venus would
become neutral in its heating effects, being neither obstructive
nor auxiliary to the sun's heat. At this period we have all
the conditions conducive to the spread of vegetable life over
the land-surface.
347. From the period of greatest obscurity by the conden-
sation of the nebular globe of Venus to that of neutrality of
this planet's effects upon the sun's radiation, would be the time
of greatest deposition of snow upon the cooler portions of the
earth during the winter solstice. Through this period the
earth's crust, being much thinner than at present, would
be more sensitive to upheaval and intrusion of plutonic
matter beneath the surface from pressure of the snow at the
poles bearing down the polar surface rocks. There would
therefore be evidence of plutonic action, taken in its broadest
sense, almost synodically during this period, elevating im-
mense districts of land-areas in steps.
When Venus had condensed to an incandescent state,
plutonic and volcanic action would cease and the entire snow
at the poles would be melted, so that there would be a return
to purely aqueous conditions with elevation of sea-level.
The entire period represented by the Devonian in Great
Britain I assume to have lasted about 60 millions of years,
extending beyond the third period of our table.
348. Carboniferous Period. This would commence in the
intermittent bright fourth period of our table. The tempe-
rature of the air would be raised at the period of internal
conjunction of Venus and gradually fall, so that there would
be intermittent periods of bright sunshine followed by heavy
rains. This would produce thin intermittent stratification of
rocks upon the shores and in inland lakes. These lakes would
overflow at the rainy period and cut incipient river-channels,
leaving thereby extensive marsh-lands, which would represent
in series extending coastwards the rivers of the time. When
the sun became open in the fifth period these marsh-lands,
GEOLOGICAL PERIODS. 241
owing to the uniform temperature and general quiescence of
atmospheric conditions, would become crowded with vegetable
life, and the general conditions would also be conducive to the
evolution of amphibian life. The Carboniferous period would
extend throughout the entire fifth open period of about
306 millions of years until the commencement of the clouding
of the sun for the commencement of the formation of the
Mercury-zone.
349. The long period suggested above may be thought to
exceed that demanded for Carboniferous time by the evidences
presented by geology. The strata represented appear to be
only from about 2000 to 13,000 feet where deposits are left.
We must observe that the deposits are generally very fine, and
indicate slow intermittent formation frequently of fine wind-
borne sand without animal life, or layers of fine mud that
was disintegrated by gentle rains from the rocks into the
shallow surface pools. These were possibly filled with
delicate cellular animal and vegetable life, which has left no
remains. Such light strata were again easily eroded after
deposition under plutonic elevation, and have no doubt for
the greater part entirely disappeared, being incorporated
into later formations.
350. Permian Period. When the sun was obscured by the
incipient condensation of the Mercury-zone, the conditions
given for the first dull period when the Venus-zone was
formed, which commenced the Cambro-Silurian times, would
be nearly repeated, but now the terrestrial conditions under
which it was superimposed would be entirely different. The
earth's crust would have greatly thickened by cooling, so
that the tropical ocean-bottom would no longer heat the
superimposed waters in a sensible degree to cause great
evaporation over these regions, as in Silurian times, and
heavy warm rains over polar regions therefrom. The general
surface-strata would also be cooled down, so that the con-
ditions of cooling which in the case of the Silurians induced
K
242 NOTES ON THE NEBULAR THEORY.
the spread of pelagic life would in this latter case cause
its destruction. The general cooling of the earth .at this
period by the obscuration of the sun's heat therefore pro-
bably caused a steady drain of vapours from the surface of
the ocean, seas, and lakes, which was deposited as snow upon
the higher land-surface. The lakes on evaporation left saline
deposits in their beds, combined with fine dust or sand blown
from the higher rocks disintegrated by frost. The accumu-
lation of snow over all the present circumpolar temperate
lands caused, by its pressure upon the still semi-fluid lower
rocks, the general elevation of lands of the earlier periods
more distant from the poles, floating these up bodily in
some districts and by local disturbance with unconformity in
others.
351. It is during the Permian period as it is represented
in Great Britain that we find the dying out of palaeozoic
life. In the early most obscure period possibly the conditions
were such that life became extinct within the entire present
temperate regions of the globe, except in the deep waters of
the ocean. Upon the earth's surface within the tropics alone,
where the dim sun could effectively diffuse its direct though
obscure rays, prevalence of life was possible.
352. In the continuity of life after the dull period we have
directly the reverse conditions to those that ruled after the
earlier dull Silurian period. We have life spreading from the
tropics instead of from the poles. The migratory species that
could reach the temperate shores were also generally much
more highly organized and locomotive, and adapted to bring
in the important factors of animal existence in the new era of
the Mesozoic period.
This dull Permian period would break into the period of
the separation of the Mercury-zone, by which an intermittent
period would be caused, again producing rapid changes of
ihin stratification of rocks, not at first conducive to the
existence of organic life till the condensation of Mercury
GEOLOGICAL PERIODS. 243
ceased to obscure the sun. What we may possibly define
as the Permian period lasted nearly through the sixth dull
period, which, according to our table, p. 225, would be about
60 millions of years.
353. Triassic and Rhcetic Periods. This division would
complete the second dull to bright intermittent period, when
Mercury was formed as a nebulous planet obscuring the sun
when in inferior conjunction. The rapid changes produced
in temperature would cause rapid deposition of rocks and
greatly restrict the conditions of organic life ; but gradually
the volume of Mercury would become less before entering
into the state of an incandescent planet and more calm
conditions would prevail. The Triassic period would last
about 47 millions of years, completing the open to dull period.
354. Jurassic Period. The eighth of our table or the second
auxiliary period. We again enter into a time particularly
adapted to the rapid evolution and spread of pelagic organic
life. The sea-shores by the intermittent rainy conditions
due to temperature changes, yet always warm, became
covered with fine mud from the land-areas, bringing down
with it abundance of support for a suitable class of littoral
life, carrying at the same time into the deeper oceans carbonate
of lime in solution available for all forms of life depending
upon it. This period would extend throughout the eighth
division of our table, for about 37 millions of years.
355. Cretaceous and Eocene Periods onwards to tlie present
Time. These may have been partly contemporary if we
imagine that the Chalk was a formation more distant from
the ancient shores, which was continuously over-deposited in
some areas, while elsewhere it was covered by argillaceous
rocks, as the land-surface was degraded. This is taken to
represent the ninth period of our table. This period, under
constant diminution of the sun's disc, would be generally
equable, producing only gentle deposition of rocks locally
in drainage-basins or in the distant ocean-bottom. It would
244 NOTES ON THE NEBULAR THEORY.
otherwise be only subject to the set of changes that were
due to the condition of the sun at the critical temperatures
of its former nebulous surroundings, which may have pro-
duced occasionally more or less obscure periods, to which
we may add the changes due to eccentricity of orbit and
variation of axis, which have produced great changes in
climate. This long period drifts us into the present time,
when the sun's disc has become very small relatively to what
it was in the past and of intense light and heat.
The period set aside by our table to include the Cretaceous
and Tertiary periods is 532 millions of years. This may
appear long for the number of superficial changes that are
evident upon the surface from the amount of mineral matter
deposited. In such a uniform period the variations were
probably all local and for the most part intermittent through
the periodical astronomical changes, so that land was alter-
nately deposited and degraded many times without producing
any great entire depth of strata *.
356. With regard to life, our only true index of time in
this period, we may conclude that where there is a general
constancy of like conditions there is little reason for change
for adaptibility to the circumstances present, particularly if
the organism is elevated to a condition of migratory instinct
for accommodation to the seasons. Therefore, seeing that
the changes have been great, the evolution period must have
been immense to have produced the variation in forms which
we know to have occurred in this period, more particularly in
that of the elevation of the scale of the higher mammals.
The changes within the tertiary period present wonderful
variations in the structure of the mammalia to give the number
of species we at present possess without consideration of the
number extinct. There is one mark, however, of continuous
progress throughout all this period the brain constantly
* Appendix C.
GEOLOGICAL PERIODS. 245
grows larger in relation to the bulk of the animal. This is
possibly a very slow continuous progressive feature, which
may give us some idea of the enormous extent of time
embraced within this period.
357. We may generally postulate from geological evidence
that in the long Tertiary period we have had present the
conditions proposed by Lyell, in his ' Principles of Geology,'
for the entire system of deposition of surface rocks, wherein
every deposit is assumed to depend upon local circumstances,
and the rocks of the past to be simply disintegrated and
redeposited without any important change in the cosmic
state.
358. In the above discussion of periods the effects of
changes of eccentricity of orbit and variations of the obliquity
of ecliptic have only just been mentioned. These variations,
there is no doubt, produced marked effects and caused
changes of climate locally which have produced minor
divisions in stratified rocks. This subject has been ably
discussed by others, and probably in some cases its import-
ance has been much exaggerated *.
359. There are also many conditions that have materially
affected the contemporary stratification, which depends greatly
upon the sea-level of the period, some of these have been
considered, but they still leave generally a wide field for
future investigations. The most important is the study of
the equilibrium of the earth's mass as a gravitation system
in rotation under the superficial changes of surface rocks
that are evident in periods of the past ; thus, for instance,
the greater or less elevation of ice at the South Pole would
disturb the gravitation centre. A past reaction of ice at the
North Pole, which probably, upon conditions proposed above,
was the direct cause of elevation of the entire plateau of
* Lyell's f Principles of Geology,' vol. i. p. 272 ; Author's paper, British
Association Reports, 1884, p. 723.
246 NOTES ON THE NEBULAE THEORY.
Central Asia. This would again react on the earth's equi-
librium. Both of these systems would tend to lower the
sea-level of Great Britain; but the subject is too large to be
even sketched in the present treatise.
360. Glacial Period. As regards this period, which neces-
sarily comes within the ninth division, this, as a consequence
of the natural diminution of the sun's volume, has been
discussed in Chapter XIII. My early reflections upon this
subject, when strongly imbued with the Huttonian principles
developed by Lyell, led me to think that there were probably
indices of sufficient change under local conditions with slight
variations of elevation of land-areas to account for this epoch
in Europe. These conclusions were mainly based upon my
idea that the movements of aerial and oceanic currents are
caused by the expansion of the atmosphere, and in less degree
of the oceanic surface, by the heat of the sun in its apparent
diurnal motion through the tropics driving before it an expan-
sion-wave of air and water *. This as a systematic motion,
according to my theory, would produce whirls or cyclones
lateral to the tropics, the position of which would depend upon
the resistance of the coast-lines. Under these conditions the
resistances that locate the North- Atlantic whirl are the coasts
of North America. The peculiar conformation of this
coast at the present time deflects the North-Atlantic
whirl into a bi-whirl, of which the northern part that
is, the Gulf Stream crosses the Atlantic, passes along
the coast of Norway, enters the Arctic Circle, and is de-
flected back to its origin after passing along the coast of
Greenland, which it leaves glaciated by the cold Arctic
current. This direction of rotation is quite abnormal to that
of any other lateral tropical whirl. It is clear, as stated in
my paper read before the British Association in 1885 f, that if
* Fluids/ p. 626.
t Brit. Assoc, Reports, 1885, p. 1020.
GEOLOGICAL PEKIODS. 247
the lower central lands of North America were only sunk some
300 feet from the mouth of the Mississippi through to Hudson's
Bay, a result readily produced by cosmic causes already
discussed, this whirl would then take its normal course, as
other lateral whirls in the South Atlantic, Pacific, and Indian
Oceans. Under these conditions Northern Greenland would
be placed in the tropical current and enjoy a very temperate
climate, and the returning Arctic oceanic and aerial current
would bathe the coasts of Western Europe, leaving icebergs
on the coast with inland glaciation, as at present in Green-
land, This would include also the glaciation of the northern
part of Great Britain.
361. To account for the glaciation of Northern America
upon like principles to the above, we should require the mean
temperature of the Northern Pacific Ocean to be sufficiently
high for its whirl deflection to keep the Behring Sea open, so
that the Northern Pacific whirl could continue its direct
motion in open water north of Alaska, bringing the return
Arctic aerial currents into the valley of the Mackenzie River
and through the Great Bear and Great Slave Lakes into
the valley of the Missouri, laden with sufficient moisture to
produce a contemporary glacial period in the northern parts
of the South-western States and distribution by currents
through the lateral valleys.
362. The considerations which have made me somewhat
modify this idea, without change of the principles suggested
so far as they are active, were due to a more attentive study of
American geology. The glaciation of Arctic North America
appears to have been greater than these principles would
entail. This to my mind is seen most particularly, according
to my theory, in the evidence of the great outflow of basalt
in the region of the Snake Biver, Idaho,- within tertiary
times. To produce this great outflow of lower heated rocks
upon principles herein discussed, there must have been very
great elevation of ice, most probably about the North Pole.
248 NOTES ON THE NEBULAR THEORY.
I assume that a pressure system of ice at the poles would
react throughout the entire lower viscous rocks; hut as these
rocks are assumed to be supported by flotation upon the-
denser metallic nucleus, ihe reaction by protrusion to restore
gravitation-equilibrium at a distance from either pole would
be much more frictional than that from a nearer pole. The
mass of basalt protruded in Idaho possibly equals the entire
mass of land above the oceanic surface in Great Britain *.
There was also contemporary elevation of the great plateau
of Central Asia. There may therefore have been an ice-cap
in the north, somewhat equivalent to that of the Antarctic
Circle. The cold necessary to produce such an ice-cap we
can scarcely imagine to have existed at the present mean
temperature of the globe. It is therefore more consistent to
assume that the effective radiation of the sun was diminished
for a period, probably, as I have proposed, by clouding in the
condensation of nebular matter at its critical temperature, p. 74.
This cannot, however, destroy the evidence of glaciation. being
at any time local in intensity, and the marine shells in the
glacial clays indicate an open ocean poleward f. There is
said to be no evidence of glaciation in the great plains of
Siberia, and from my own observation there has been none
in the west of Norway ; for instance, upon the granitic and
gneiss rocks of the Lofoten Isles which retain the sharp
pointed outlines of ancient rocks that have been subject to
weathering only throughout long geological periods J.
For great elevation of circumpolar land or massive outflow
of basalt at any period, the extreme cold of the previous
period may have produced great rigidity in the ice-system
and contiguous rocks. The reaction of such a system would
cause the more distant parts of the earth's crust to give way
* Geikie, ' Geology/ p. 257.
t ' Acadian Geology/ Sir J. W. Dawson, p. 65.
J Author's paper, Geol. Soc. Proc., Feb. 23, 1887.
FUTURE PERIOD. 249
paroxysmally and after fracture to continue the effects of the
reaction until the polar pressure reached nearly its point of
equilibrium. In this manner reactions of ice-pressures would
be periodical upon the surface system of rocks.
363. Future Period. By the continuity of the conditions
which now rule, the sun will not probably become a much
brighter incandescent body than it is, and it will decrease
in volume and ultimately in incandescence. The ice-caps
which cover the Antarctic and probably the Arctic pole
must therefore grow more extensive with the decrease of
solar heat ; and although increase of weight of ice may
cause deflection of the crust and distribution of pressure
upon the interior highly heated rocks, which pressures
may react in producing plutonic and volcanic phenomena,
still, with each such displacement the crust will become
thicker, more rigid, and more resistant, and thereby vol-
canic and plutonic action to overcome the resistance will be
more paroxysmal. The oceans also, by the condensation of
evaporated water and its deposition in the form of -ice at
the poles, will become of less depth, so that land-areas will
increase in aerial surface.
364. The periodic process would therefore appear to be a
general decrease of temperature accompanied by apparent
elevation and spread of continental lands and decrease of
oceanic area, so that the temperate inhabitable globe would
increase over tropical areas for a long period in greater ratio,
possibly, than the circumpolar areas and would cease to be
sufficiently temperate for the existence of organic life.
At a later period the evaporation from the tropical oceans
would be less, and deposition in circumpolar areas less, and
the earth's crust more rigid, so that the sea would diminish
less by this cause; but at the same time the mountainous lands
surrounding the great oceans would have the snow-line
lowered, so that a part of the evaporation from the oceans would
fall upon the adjacent lands instead of drifting poleward,
250 NOTES ON THE NEBULAE THEORY.
and the lower shelving shores of the much reduced tropical
oceans would hecome habitable lands.
At a still later period the tropical ocean-beds would be
drained by evaporation in clouds drifting over to the shores,
which for the most part would never return to them in the
frozen river-streams. The earth would then possess three or
four oceanic areas adapted to life only the lower beds of the
Pacific, Atlantic, and Indian Oceans.
Later when the sun presented only a dull red disc, appear-
ing to move daily across the starry vault, the lands repre-
senting the deep ocean-beds would be frozen and life gradually
become extinct.
365. The entire cloud-drainage of the great oceans and
the snow-clad mountainous lands surrounding them would
release the pressure upon the deep ocean-beds in proportion
to the increase of the weight of snow upon the mountains.
The earth would probably still be sufficiently yielding in its
interior to admit of a certain amount of reaction by distribu-
tion of surface-pressures, by which the ocean-beds would be
elevated to restore partial gravitation-equilibrium. This
effect would probably be produced by distribution of small
volcanoes over the former lower oceanic surface, and, as the
surface would be shrinking slightly by loss of temperature,
there would occur also paroxysmal upheavals in localities
where, through the tension and plutonic pressure below the
surface, resistance would be overcome. This would leave
earthquake-fissures as a permanent surface-feature.
366. It is possible that in one of the warmer tropical
valleys running east to west formed from one of the above-
described fissures in the deepest bed of the Pacific, and near
to some residual thermal springs, the last individual, of the
latest evolved form of humanity, may die of hunger and close
for ever the records of science attained upon our globe.
Whether extinction of life will occur within the short
period of 15 millions of years, as suggested by the theory of
FUTURE PERIOD. 251
Helmholtz for the sun to decrease to the density of the earth,
can scarcely be suggested. Whether we know the sun's
specific heat or the law of dispensation of solar heat into
space is doubtful ; but the probability is that world-life will be
longer than this, if we can accept the conditions which I have
reserved for discussion in Appendix A as my theory on this
point may be thought not to be a necessary part of our
subject.
[ 252 ]
APPENDIX A.
I MAY offer as a pure hypothesis that the energy of a light-
and heat-giving system may not be so rapidly dissipated as we
know it to be by experiment unless it meet in radiation with
another material body as a recipient. In fact, that for the
rapid diffusion of light and heat through cosmic space there
must be one or more motive couples, just in the same way
as this is necessary for the action of gravitation-energy, only
that light and heat bear reference to surface only, not to mass.
Upon this hypothesis light and heat, as possibly gravitation,
may be considered in certain cases as phenomena of induction,
and in action, in a certain degree as regards the sun,
resemble the discharge from one excited conductor to another
through an insulated medium. The intensity of propagation
of forces from the sun's globular mass being assumed equal
to that of the discharge of electricity from a point into a
space of direct insulation that is, insulation from general
diffusion, so that the induction to another body if present
falls in direct line only, with the loss only of a limited
amount by free radiation. In this case the form of force is
nevertheless that of light or heat, not of electricity, from
which it may vary in any motive degree. A theory upon
these lines, to which I have devoted some years of study,
but cannot extend here, except to state the principle, would
account for there being snow-caps about the poles of Mars,
whereas, from his distance being taken inversely as the square
in comparison with that of the earth, the amount of sun-heat
APPENDIX A. 253
capable of reaching the surface of this planet would leave it
wholly frozen. The intensity of the light of Jupiter and
Saturn also far exceeds that due to the reflection of the sun's
light as deduced from calculation of uniform radiation only.
Upon these principles, if they hold, it may be suggested that
we should materially conserve solar energy, for however
closely light induction couples may fill up the radiants about
the sun, the open interspaces where there would be less loss
of energy must be of immensely greater area that is, as
the space to the mass. Further, the sun would receive as much
light- energy from another star as it would impart to this
star, so that the radiant force dissipated would be principally
upon the planets that is, upon bodies cooler than itself.
Such a principle of dispensation of heat and light would
prolong the sun's future life to many times the period esti-
mated by Helmholtz.
To separately define the forces active upon a planet in
relation to the sun in factors of induction according to this
hypothesis, I would suggest :
Gravitation. Mass Induction, producing a tendency to draw
two bodies together whose equilibrium is only satisfied when
the attraction produces a unit globular mass.
Heat. Conductive Induction, by which a certain depth
of mass is affected in diminishing ratio in intensity by some
geometrical power. This force is probably, if taken per se,
repulsive.
Light. Surface Induction, affecting the surface molecules
only to a limited depth, except in special or dioptric bodies,
through which it passes to other bodies by a system of radial
conduction to the inductive body beyond. This force is also
per se probably repulsive.
As I may never publish my researches on this subject, I
may say that my idea of light is that its induction renders
all bodies under its influence luminous to a certain extent.
That this self-luminosity induces a like secondary luminosity
254 NOTES ON THE NEBULAR THEORY.
in another body or a similar effect upon the retina of the eye
or a sensitive film in a camera. That this luminous action is
probably caused by rotating the surface molecules so as to
cause them to present the surface which affinity in the dark
draws inwards to an outward position. A complete revolu-
tion being necessary for white, and a partial revolution for
colour. But this last stated idea is immaterial, the self-
luminosity is material. To mention one of my first
experiments. I made in 1873 a drawer 6 by 6 inches, of one
inch in depth, very carefully fitted in a velvet-lined frame to
exclude light. The inside of the drawer could be exposed to
sunshine while it was closed and drawn into a dark room
when required. I attached two spiral springs to the front of
the drawer and a catch to keep it closed when out in the sun-
shine, so that when the catch was released the drawer came
instantly into the dark room. I tried many experiments ; the
first was that of writing my name boldly in Indian ink upon
a piece of white paper. After this had been a minute or less
in the sunshine, and was then drawn into the dark room, I
found that I could read it easily for a short time in the dark ;
therefore, I conclude it retained a part of its luminosity, or
at least, if it was luminous in the dark, it must have been also
luminous in the sunlight, so that its perception to the eye could
not have been entirely from reflected sunlight as generally
assumed. It appears to me, therefore, that we are bound
to admit induced luminosity as a factor of visibility. These
effects, as phenomena ascribed to phosphorescence, are well
known, and have been investigated most ably by Becquerel ;
but my idea of them is that they are not, as assumed, simply
phenomena of phosphorescence, but of induced luminosity,
and that they are universal for all light-giving bodies, that
is, for all visible bodies or such as are not dioptric, or for
black bodies, if any exist, or so far as they exist. In this
hypothesis it is not necessary to suppose that a body may
retain its induced luminosity for an instant in the dark.
APPENDIX A. 255
Heat conductors, that is metallic bodies, possess no such
power of retention, the surface molecule being assumed in
this case to be sensitive instantly to light and heat influences.
This does not affect the laws that govern the action of light,
such as the reflective properties under the condition that a
body may receive luminous induction in one direction and
dispense it at coincident equal angles, or the refractive
properties of dioptric bodies, by which the inducing rays
are bent, only that in this last case the inductive body
is behind the dioptric, which acts only as a conductor thereto
in the same manner as a metal wire does to electricity, but
following its own laws. The direction of the light force of
induction is otherwise always in direct line. My experiments
upon these hypotheses were made in 1872-4, and I have
discussed some of them with my friends. Some of these ideas
appear to have occurred to a correspondent of the ' English
Mechanic,' T. W. B., last year, 1894, and, so far as that publi-
cation goes, I acknowledge the priority if it is of any value.
In the multiplicity of thoughts, by reason of our similarity
of organism, some of our ideas must be like those of other
individuals.
[ 256 ]
APPENDIX B.
THE generally accepted theory of land-formation is that
which was proposed or maintained by the late "Robert Mallet
in a paper upon " The amount of Energy developed by the
Secular Cooling of the Earth," contained in two papers, over
100 pages, in the Phil. Trans. 1874-5. According to these
papers the amount of heat lost from the initial temperature of
the earth will represent the force of its contraction. The
amount of this energy is presumed to be made evident in
compression of the superficial strata causing the elevation,
inclination, and crumpling of the strata and the entire
volcanic phenomena. The data, upon which the arguments
of these papers rest, are assumed to be taken from calculations
of Elie de Beaumont, Forbes, and Lord Kelvin, who estimate
the heat lost by the earth to be equal to the melting of a
plate of ice, respectively of 0'0065, 0*007, and 0-0085 milli-
metres annually. From these data it is stated that from 575
to 777 cubic miles of ice melted annually would represent the
loss of heat. By going over the calculations in this paper, I
was able to point out a considerable error in it, sufficient to
upset the whole contraction theory upon the lines laid down
by Mr. Mallet. After writing to Sir George Stokes, then
Secretary to the Royal Society, who clearly saw the acci-
dental error, I read a paper upon it before the Geological
Society * in June 1884, showing that the contraction from the
data given was only about one cubic mile annually, that is,
* Quart. Journ. Geol. Soc. vol. xl. (Proc.) p. 67.
APPENDIX B. 257
from -7937 to 1'03S7 mile. The principal authority for the
data given was Lord Kelvin ; and as I could not find any
reference to the subject in his papers, Sir George Stokes
kindly wrote to Lord Kelvin for me about this, and found
that the assertion was altogether a mistake. Lord Kelvin
never made such a calculation, therefore this theory, sup-
ported upon the evidence of compression of surface-strata, is
generally without foundation in fact. I think, moreover, that
the contraction theory is quite opposed to observation of actual
rocks, the joints of which are generally open below the surface,
and show the effects of pressure from beneath producing a
tensile strain upon the surface to form the open joints. These
joints are often filled with basalt from intrusion of the under-
lying magma, showing more directly evidence of the outward
pressure of heated liquid plutonic matter.
[ 258 ]
APPENDIX C.
IF the general theory of this work is accepted at some future
time, a more experienced practical geologist than myself
may shift the divisions in the rock-series that I have adopted
to make them more exactly agree with the periodic conditions
proposed. To do this perfectly would require refined geolo-
gical observation, as the astronomical changes herein defined
could not have been generally abrupt, so as to produce very
distinct divisions in stratifying rocks. Further, there must
be superimposed upon the greater astronomical changes herein
suggested, the minor influences of variation of eccentricity
of orbit and change of obliquity of axis, which would produce
variation of deposition although possibly not to the extent
proposed by Croll and Lyell. Some objection, for instance,
may be made to my grouping the cretaceous with the tertiary
in one long period, wherein the chalk formation is at least
very distinct, and locally no doubt, if taken in vertical series,
the more ancient. In this case we may consider the chalk to
be a deep oceanic formation that is still in progress, a theory
generally accepted since the ' Challenger ' Expedition. I
think a system of contemporary stratification of the various
kinds of sediment distinguished by special chemical elements
must have been general throughout all time, as we have
only one set of such elements largely to deal with upon the
surface of the globe, however much they may have been
churned up or sorted out by local prevailing conditions.
Upon this suggestion we could at no period have had one
APPENDIX C. 259
general system of deposition prevailing either of silica,
alumina, or calcic-carbonate, in other than local areas. The
general scheme of deposition in quiescent times and undis-
turbed by oceanic currents may be shown diagrammatically
by the figure above, which may represent, say 200 miles
of, deposition from a coast of the ancient rock-surface of a
certain period : O, the oceanic surface ; a line from the
ancient rock to a point F the surface of the newly-formed
rocks, where a band of flints occur in the chalk from organic
deposition at a certain distance from the coast. Then of the
produce of the disintegrated rocks, the coarser materials
would rest at B ; the broken masses of silica or sand at S ; the
lighter mud or clay at C ; the perfectly soluble carbonate of
lime and silica at CH, where it would be generally absorbed by
organic life. This system would in all cases form sets of rocks
and go on continuously over areas of surface-drainage carrying
the disintegrated rocks if undisturbed by oceanic currents or
tidal action, and could in the past only be arrested by such
great astronomical changes as herein proposed. These greater
changes cannot occur again, so that the present period may
be geologically indefinitely extended for the time the ocean
retains its liquidity.
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