cold materials would generate heat, and, therefore, that the
resulting planetary masses would assume the liquid form; that
Jupiter and Saturn are now in the liquid state; and that all
the planets will ultimately become cold and solid. This is in
fair agreement with present-day opinion as to the planets, save
that modern astronomers go further in holding that the outer
strata of Jupiter and Saturn, likewise of Uranus and Neptune,
down to a great depth, must still be gaseous. In 1785, after
the principle of heat liberation attending the compression of a
gas had been announced, Kant supplemented his statement of 1755
as to the origin of the Sun's heat. He attributed this to
gravitational action of the Sun upon its own matter, causing it
to contract in size: he said the quantity of heat generated in
a given time would be a function of the Sun's volumes at the
beginning and at the ending of that period of time. This is
substantially the principle which Helmholtz rediscovered and
announced in 1854, and which is now universally accepted--with
the reservation of the past ten years, that radioactive
substances in the Sun may be an additional factor in the
problem.
Kant's paper of 1754 enunciated the theory that the Moon always
turns the same face to the Earth because of tidal retardation
of the Moon's rotation by the Earth's gravitational attraction;
and that our Earth tides produced by the Moon will slow down
the Earth's rotation until the Earth will finally turn one
hemisphere constantly to the Moon. This principle was in part
reannounced by Laplace a half century later, and likewise
investigated by Helmholtz in 1854, before Kant's work was
recognized.
Kant's speculations on a possible destruction and re-birth of
the solar system, on the nature of Saturn's ring, and on the
nature of the zodiacal light are similar in several regards to
present-day beliefs.
Kant wrote:
'I seek to evolve the present state of the universe from the
simplest condition of nature by means of mechanical laws
alone.'
In 1869 Sir William Thomson, afterwards Lord Kelvin, commented
that Kant's
'attempt to account for the constitution and mechanical origin
of the universe on Newtonian principles only wanted the
knowledge of thermodynamics, which the subsequent experiments
of Davy, Rumford and Joule supplied, to lead to thoroughly
definite explanation of all that is known regarding the present
actions and temperatures of the Earth and of the Sun and all
other heavenly bodies.'
These are, apparently, the enthusiastic comments resulting from
the re-discovery of Kant's papers. A present-day writer would
not speak so decisively of them, but we must all bow in
acknowledgment of Kant's remarkable contributions to our
subject, published when he was but 31 years old.
LAPLACE'S HYPOTHESIS
In 1796, 41 years following Kant's principal contributions,
Laplace published an extensive untechnical volume on general
astronomy. At the end of the volume he appended seven short
notes. The final note, to which he gave the curious title "Note
VII and last," proposed a theory of the origin and evolution of
the solar system which soon came to be known as Laplace's
Nebular Hypothesis. There are several circumstances which
indicate pretty clearly that Laplace was not deeply serious in
proposing this hypothesis:
1. Its method of publication as the final short appendix to a
large volume on general astronomy.
2. He himself said in his note that the hypothesis must be
received "with the distrust with which everything should be
regarded that is not the result of observation or calculation."
3. So far as we know he did not submit the theory to the test
of well-known mathematical principles involved, although this
was his habit in essentially every other branch of astronomy.
4. Laplace, in common with Kant, laid great stress upon the
fact that the satellites all revolve around their planets from
west to east, nearly in the common plane of the solar system;
yet 6 or 7 years before Laplace's publication, Herschel had
shown and published that the two recently discovered satellites
of Uranus were revolving about Uranus in a plane making an
angle of 98 degrees with the common plane of the solar system.
While Laplace might not have known of Uranus's satellites in
1796, on account of existing political conditions, there is no
evidence that he considered or took note of the fact when
making minor changes in his published papers up to the time of
his death in 1827. It is a further interesting comment on
international scientific literature that Laplace died without
learning that Kant had worked in the same field.
Laplace and his contemporary, Sir William Herschel, had been
the most fruitful contributors to astronomical knowledge since
the days of Sir Isaac Newton. Herschel's observations had led
him to speculate as to the evolution of the stars from nebulae,
and as a result interest in the subject was widespread. This
fact, coupled with Laplace's commanding position, caused the
nebular hypothesis to be received with great favor. During an
entire century it was the central idea about which astronomical
thought revolved.
Laplace conceived that the solar system has been evolved from a
gaseous and hot nebula; that the nebulosity extended out
farther than the known planets; and that the entire nebulous
mass was endowed with a slow rotation that was UNIFORM IN
ANGULAR RATE, as in the case of a rotating solid. This gaseous
mass was in equilibrium under the expanding forces of heat and
rotation and the contracting force of gravitation. Loss of heat
by radiation permitted corresponding contraction in size, and
increased speed of rotation. A time came, according to Laplace,
when the nebula was rotating so rapidly that an outer ring of
nebulosity was in equilibrium under centrifugal and
gravitational forces and refused to be drawn closer in toward
the center. This ring, ROTATING AS A SOLID, maintained its
position, while the inner mass contracted farther. Later
another ring was abandoned in the same manner; and so on, ring
after ring, until only the central nucleus was left. Inasmuch
as the nebulosity in the rings was not uniformly distributed,
each ring broke into pieces, and the pieces of each ring, in
the progress of time, condensed into a gaseous mass. The
several large masses formed from the abandoned rings,
respectively, became the planets and satellites of the solar
system. These gaseous masses rotated faster and faster as their
heat radiated into space, they abandoned rings of gaseous
matter just as the original mass had done, and these secondary
rings condensed to form the satellites; save that, in one case,
the ring of gas nearest to Saturn for some reason formed a
solid (!) ring about that planet, instead of condensing into
one or more satellites. Thus, in outline, according to Laplace,
the solar system was formed.
The first half of the nineteenth century found the nebular
hypothesis accepted almost without question, but a tearing-down
process began in the second half of the century, and at present
not much of the original structure remains standing. This is
due in small part to discoveries since Laplace's time, but
chiefly to a more careful consideration of the fundamental
principles involved. We have space to present only a few of the
more salient objections.
1. If the materials of the solar system existed as a gas,
uniformly distributed throughout what we may call the volume of
the system, the density of the gas would be exceedingly low: at
the most, several hundred million times less dense than the air
we breath. Conditions of equilibrium in so rare a medium would
require that the abandonment of the outer parts by the
contracting and more rapidly rotating inner mass should be a
continuous process. Each abandoned element would be abandoned
individually; it would not be vitally affected by the elements
slightly farther out in the structure, nor by the elements
slightly nearer to the center. Successive abandonment of nine
gaseous rings of matter, EACH RING ROTATING AS IF IT WERE A
SOLID STRUCTURE, is unthinkable. The real product of the
cooling process in such a nebula would undoubtedly be something
in the nature of a spiral nebula, in which the matter would
revolve around the nucleus the more rapidly the nearer it was
to the nucleus. If the matter were originally distributed
uniformly throughout the rotating structure, the spiral lines
might not be visible. If it were distributed irregularly, the
spiral form here and there could scarcely fail to be in
evidence to a distant observer.
2. Laplace held that the condensation of each ring would result
in one planet, rotating on its axis from west to east; this
apparently by virtue of the fact that in a ring rotating AS A
SOLID the outer edge travels more rapidly than the inner edge
does, and therefore, the west to east direction of rotation
must prevail in the planetary product. If now, as we firmly
believe, each constituent of such an attenuated ring must
rotate substantially independently of other constituents, those
nearer the inner edge of the ring will possess the higher
speeds of rotation, and the preponderance of kinetic energy in
the inner parts of the ring should give the resulting planetary
condensation a retrograde direction of rotation.
3. According to Laplace the satellites should all revolve
around their primaries from west to east. Eight of the
satellites do not follow this rule.
4. If the materials composing the inner ring of Saturn were
abandoned by the parent planet, as this planet contracted in
size and rotated ever more and more rapidly, then the ring
should revolve about the planet in a period considerably longer
than the planet period. The reverse is the fact. The rotation
period of the equatorial region of the planet itself is 10 h.
14 m., whereas the inner edge of the ring system revolves about
the planet once in about five hours.
5. The inner satellite of Mars revolves once in 7 h. 39 m.,
whereas Mars requires 24 h. 37 m. for one rotation. According
to the Nebular Hypothesis, the period of the satellite should
be the longer.
6. Laplace's hypothesis would seem to require that the orbits
of the planets be circular or very nearly so. The orbits of all
except Venus and Neptune are quite eccentric, and Mercury's
orbit, which should have the nearest approach to circularity,
is by far the most eccentric.
7. If the planetary rings were abandoned by centrifugal action,
we should expect the Sun to be rotating in the principal plane
of the planet system. The major planets, from Venus out to
Neptune, are revolving in nearly a common plane. The Sun,
containing 99 6/7 per cent. of all the material in the system,
has its equator inclined 7 degrees to the planet plane. This
discrepancy is a very serious and I think fatal objection to
Laplace's hypothesis, as Chamberlin has emphasized.
8. Laplace assumed a nebula whose form was a function of its
rotational speed, its gravitation, its internal heat, and,
although he does not so state, of its internal friction. He did
not distribute the matter within the nebula to conform in any
way to the distribution as we observe it to-day, but he let the
entire structure contract, following the loss of heat, until
the maintenance of equilibrium required the successive
abandoning of seven or eight rings. He mentions a central
condensation, but gives no further particulars. Thirty years
ago Fouche established clearly that the condensing of Laplace's
assumed nebula into the present solar system would involve the
violent breaking of the law known as the conservation of moment
of momentum. Fouche proved that a distribution of matter beyond
any conception of the subject by Laplace must be assumed. Fully
96 per cent. must be condensed in the central nucleus AT THE
OUTSET, and not more than 4 per cent. of the total mass must
lie outside of the nucleus and be widely distributed throughout
the volume of the solar system. Chamberlin puts the case very
strongly in another way. If the planet Mercury was abandoned as
a ring of nebulosity, the equatorial velocity of the remaining
central mass must at that time have been in the neighborhood of
45 km. per second, as this is the orbital speed of Mercury. If
the central mass condensed to the present size of the Sun, the
Sun's equatorial velocity of rotation should now be fully 400
km. per second, in accordance with the requirement of the rigid
law of constancy of moment of momentum. The Sun's actual
equatorial velocity is only 2 km. per second!
In several other respects the hypothesis of Laplace, as he
proposed it, fails to account for the facts as they are
observed to exist.
Poincare devoted his unique talents to the evolution problem
shortly before his death. He recognized that the Laplace
hypothesis is not tenable except upon such an assumed
distribution of matter as was defined by Fouche. Accepting this
modification, and extending the hypothesis to involve the
application of tidal interactions at many points throughout the
solar system, Poincare expresses the opinion that the Laplacian
hypothesis, of all those proposed, is still the one which best
accounts for the facts.[3] However, he does not utilize the
hypothesis of rings rotating as solids, for he finds it
necessary to conclude that the planetary masses in the
beginning must have had retrograde rotations. In the large
planetary masses of Jupiter and Saturn, for example, the
materials which form the outer retrograde satellites were
abandoned while the rotations were still retrograde, and when
the diameters of the planetary masses were several scores of
times their present diameters. In these extended masses the Sun
would create tidal waves, and here, as always, such waves would
exert a retarding effect upon the rotations. A time would come,
Poincare thought, when these planets would rotate once in a
revolution; that is, present the same face to the Sun; and this
is in fact a west to east rotation. Further contraction of the
planetary masses would give rise to increasing rotational
speeds in the west to east direction. The materials which form
the inner satellites of Jupiter and Saturn were abandoned
successively after the west to east direction of rotation had
become established. According to modifications of the same
theory, tidal retardation has slowed down Saturn's speed since
the abandonment of the materials which later condensed to form
the inner ring of that planet; or, possibly, the ring materials
encountered resistance after the planet abandoned them, with
the consequence that the ring drew in toward the planet and
increased its speed; and similarly in the case of Mars and its
inner satellite.
[3] Poincare has made the following interesting comments on
Laplace's hypothesis: "The oldest hypothesis is that of
Laplace; but its old age is vigorous and for its age it has not
too many wrinkles. In spite of the objections which have been
urged against it, in spite of the discoveries which astronomers
have made and which would indeed astonish Laplace himself, it
is always standing the strain, and it is the hypothesis which
best explains the facts; it is the hypothesis which responds
best to the question which Laplace endeavored to answer, Why
does order rule throughout the solar system, provided this
order is not due to chance? From time to time a breach opened
in the old edifice (the Laplace hypothesis); but the breach was
promptly repaired and the edifice has not fallen."
To me this modification of the Laplacian hypothesis is
unsatisfactory, for several reasons. To mention only one: if
Jupiter was a large gaseous mass extending out as far as the
8th and 9th satellites, the gaseous body was very highly
attenuated; friction in the outer strata would be essentially a
negligible quantity, and tidal retardation would not be very
effective; and it would be under just these conditions that
loss of heat from the planet should be most rapid and the rate
of increase of retrograde rotation resulting therefrom be
comparatively high. It would seem that the rotation of the
planet in the retrograde direction must have accelerated under
the contractional cause, rather than have decreased and
reversed in direction under an excessively feeble tidal cause.
The recognized weaknesses of Laplace's hypothesis have caused
many other hypotheses to be proposed in the past half century.
The hypotheses of Faye, Lockyer, du Ligondes, See, Arrhenius,
and Chamberlin and Moulton include many of the features of
Kant's or Laplace's hypotheses, but all of them advance and
develop other ideas. It is unfortunate that space limits do not
permit us to discuss the new features of each hypothesis.
(To be continued.)
PROGRESS AND PEACE
BY PROFESSOR ROBERT M. YERKES
HARVARD UNIVERSITY
LASTING peace among the nations of the earth we must regard as
of supreme moment, the discovery of the conditions thereof, as
most worthy of human effort. Physical struggle is no longer
accepted as either a necessary or a desirable means of settling
differences between individuals. Why, then, should it be
tolerated to-day in connection with national disagreements? To
admit the impossibility or the impracticability of universal
peace is to stigmatize our vaunted civilization as a failure.
Surely we will not, can not, humble ourselves by such an
admission until we have exhausted our energies in searching for
the conditions of national amity.
With my whole life I believe in the possibility and value of
worldwide friendliness and cooperation. I am writing to discuss
not the attainability or the merits of peace, but ways of
achieving it; not to criticize present activities on its
behalf, but to indicate the promise of a neglected approach and
to present a program which should, I believe, find its place in
the great "peace movement."
Must peace be achieved and maintained by brute strength,
regardless of sense and sentiment, or may it be gained through
intelligence, humanely used? Must the pathway thereto be paved
with human skulls, builded with infinite suffering and
sacrifice, or may it he charted by scientific inquiry and
builded by the joyous labor of mutual service and helpfulness?
Is it possible, in the light of the history of the races of
man, to doubt that we must place our dependence on intelligence
sympathetically employed, not on physical prowess? To me it
seems that peace must be achieved peacefully, not by the clash
of arms and bloodshed.
But even if we grant that science is our main hope, there
remains a choice of methods. On the one hand, there is the way
of material progress, physical discovery and feverish haste to
apply every new fact to armament; on the other, that of
biological research, social enlightenment, and ever-increasing
human understanding and sympathy.
Firm believers in each of these possible approaches, through
science, to international peace, are at hand. The one group
argues that nations, like individuals, must be controlled in
all supreme crises by fear; the other contends that
civilization has developed in enlightened human sympathy a
higher, a more worthy, and a safer control of behavior.
As a biologist and a believer in the brotherhood of man, I wish
to present the merits of sympathy, as contrasted with fear, and
to plead for larger attention to the biological approach to the
control of international relations. For I am convinced that the
greatest lesson of the present stupendous world-conflict is the
need of thorough knowledge of the laws of individual and social
human behavior. Surely this war clearly indicates that the
study of instinct, and the use of our knowledge for the control
of human relations, is incalculably more important for the
welfare of mankind than is the discovery of new and ever more
powerful explosives or the building of increasingly terrible
engines of destruction.
During the last half-century the physical sciences,
technologies, arts and industries, have made marvelous
advances. At enormous cost of labor and material resources
there have been discovered and perfected means of destroying
life and property at once so effective and so terrible to
contemplate that preparedness for war seemed a safe guarantee
of peace. But who is there now to insist, against the evidence
of blood-drenched Europe, that material progress, physical
discovery, and armament based thereupon, assure international
friendship?
Only if one of the nations should discover, and guard as its
secret, some diabolically horrible means of destroying human
life and property by wholesale and over materially unbridged
distances, can armaments even temporarily put an end to war. In
such event--and it is by no means an improbability--the whole
world might suddenly be made to bow in terror before the will
of the all-powerful nation. Before this approaching crisis, can
we do less than earnestly pray that the translation of physical
progress into armament may be halted until the brotherhood of
man has been further advanced? Dare we stop to contemplate what
would happen to-morrow if Germany, with half the civilized
world arrayed against her, should come into possession of some
imponderable, and to the untutored mind mysterious, means of
directing her torpedoes, exploding magazines, mines, shells
from distant bases? Undoubtedly we are close upon the
employment of certain vibrations for this deadly purpose. Shall
we veer in time and take a safer course, or are we doomed to
the inevitable?
For the certain result of pushing forward relentlessly on the
path of preparation for war--in the name of peace--is the
dominance of a single nation and the destruction or subjugation
of all others. This is as inevitable as is death. If we would
preserve and foster racial and national diversity of traits,
promote social individuality as we so eagerly foster the
diversity of selves, we must speedily focus attention upon
human nature and seek that knowledge of it which shall enable
us to control it wisely rather than to destroy it ruthlessly.
Even were I able to do so, I should in no degree belittle the
achievements of the physical sciences and their technologies,
for I believe whole-heartedly in their value, and long for the
steady increase of our power to control our environment. But
when these achievements are offered as means of creating or
maintaining certain desired conditions of individual and social
life, I must insist that other knowledge is essential--nay,
more essential--than that of the physicist or chemist.
Knowledge, namely, of life itself.
Most briefly, the situation may thus be described. In peace and
in war there are two large, complex and intricate groups of
facts to be dealt with by those who seek the welfare of man.
The one group comprises the phenomena of physical nature as the
condition of life--environment; the other is constituted by the
phenomena of life and the relations of lives. Those who
sincerely believe in preparedness for war as a preventive
measure, misconceive and attempt to misuse the emotion of fear
and its modes of expression. It is as though we should strive
tirelessly to develop machinery and methods for educating our
children, the while ignorant of the laws of child development
and branding as of no practical importance the fundamentals of
human nature.
To nations no more than to individuals is it given to live by
fear alone. By it a nation may become dominant, and diversity
of body, mind, and ideals be eradicated. To base our
civilization upon fear entails uniformity, monotony of life;
the sacrifice of peoples for the unduly exalted traits and
national ideals of a single homogeneous social group--a single
all-powerful nation. Knowledge of life, and the sympathy for
one's fellow men which springs from it, must control the world
if nations are to live in peaceful and mutually helpful
relations. If life, whether of the individual or of the social
group, is to be controlled, it must be through intimate
knowledge of life, not through knowledge of something else. The
world must be ruled by sympathy, based upon understanding,
insight, appreciation. This is my prophecy, this my faith and
my present thesis.