COSMOGONY IN TRANSITION
We have seen how Wright in 1750 initiated a theory of evolution, not
only of the solar system, but of all the stars and nebulae as well; how
Kant in 1752 by elaborating this theory sought to develop the details of
evolution of the solar system on the basis of the Newtonian law, though
weakened, as we know, by serious errors in applying physical laws; how
Laplace in 1796 put forward his nebular hypothesis of origin and
development of the solar system, by contraction from an original gaseous
nebula in accord with the Newtonian law; how Sir William Herschel in
1810 saw in all nebulae merely the stuff that stars are made of; how Lord
Rosse in 1845 discovered spiral nebulae; how Helmholtz in 1854 put
forward his contraction theory of maintenance of the solar heat,
seemingly reinforcing the Laplacian theory; how Lane in 1870 proved that
a contracting gaseous star might rise in temperature; how Roche in 1873
in attempting to modify the Laplacian hypothesis, pointed out the
conditions under which a satellite would be broken up by tidal strains;
how Darwin in 1879 showed that the theory of tidal evolution of
non-rigid bodies might account for the formation of the moon, and binary
stars might originate by fission; how Keeler in 1900 discovered the vast
numbers of spiral nebulae; how Chamberlin and Moulton in 1903 put
forward the planetesimal hypothesis of formation of the spiral nebulae,
showing also how that hypothesis might account for the evolution of the
solar system; and how Jeans in 1916 advocated the median ground in
evolution of the arms of the spiral nebulae, showing that they will break
up into nuclei, if sufficiently massive.
In all these theories, truth and error, or lack of complete knowledge,
appear to be intermingled in varying proportions. Is it not early yet to
say, either that any one of them must be abandoned as totally wrong, or
on the other hand that any one of them, or indeed any single hypothesis,
can explain all the evolutionary processes of the universe?
Clearly the great problems cannot all be solved by the kinetic theory of
gases and the law of gravitation alone. Recent physical researches into
sub-atomic energy and the structure and properties of matter, appear to
point in the direction where we must next look for more light on such
questions as the origin and maintenance of the sun's heat, the complex
phenomena of variable stars and the progressive evolution of the myriad
bodies of the stellar universe. Because we have actually seen one star
turn into a nebula we should not jump to the conclusion that all nebulae
are formed from stars, even if this might seem a direct inference from
the high radial velocities of planetary nebulae.
Quite as obviously many of the spiral nebulae are in a stage of
transition into local universes of stars--even more obvious from the
marvelous photographs in our day than the evolution of stars from nebulae
of all types was to Herschel in his day.
The physicist must further investigate such questions as the building up
of heavy atomic elements by gravitative condensation of such lighter
ones as compose the nebulae; and laboratory investigation must elucidate
further the process of development of energy from atomic disintegration
under very high pressures. This leads to a reclassification of the stars
on a temperature basis.
Equally important is the inquiry into the mechanism of radiative
equilibrium in sun and stars. Not impossibly the process of the earth's
upper atmosphere in maintaining a terrestrial equilibrium may afford
some clue. What this physical mechanism may be is very incompletely
known, but it is now open to further research through recent progress of
aeronautics, which will afford the investigator a "ceiling" of 50,000
feet and probably more. Beneath this level, perhaps even below 40,000
feet, lie all the strata, including the inversion layer, where the sun's
heat is conserved and an equilibrium maintained.
Even ten years ago, had an astronomer been asked about the physical
condition of the interior of the stars, he would have replied that
information of this character could only be had on visiting the stars
themselves--and perhaps not even then. But at the Cardiff meeting of the
British Association in 1920, Eddington, the president of Section A,
delivered an address on the internal constitution of the stars. He cites
the recent investigations of Russell and others on truly gaseous stars,
like Aldebaran, Arcturus, Antares and Canopus, which are in a diffuse
state and are the most powerful light-givers, and thus are to be
distinguished from the denser stars like our Sun. The term _giants_ is
applied to the former, and _dwarfs_ to the latter, in accord with
Russell's theory.
As density increases through contraction, these terms represent the
progressive stages, from earlier to later, in a star's history. A red or
M-type star begins its history as a giant of comparatively low
temperature. Contracting, according to Lane's law, its temperature must
rise until its density becomes such that it no longer behaves as a
perfect gas. Much depends on the star's mass; but after its maximum
temperature is attained, the star, which has shrunk to the proportions
of a dwarf, goes on cooling and contracts still further.
Each temperature-level is reached and passed twice, once during the
ascending stage and once again in descending--once as a giant, and once
as a dwarf. Thus there are vast differences in luminosity: the huge
giant, having a far larger surface than the shrunken dwarf, radiates an
amount of light correspondingly greater.
The physicist recognizes heat in two forms--the energy of motion of
material atoms, and the energy of ether waves. In hot bodies with which
we are familiar, the second form is quite insignificant; but in the
giant stars, the two forms are present in about equal proportions. The
super-heated conditions of the interior of the stars can only be
estimated in millions of degrees; and the problem is not one of
convection currents, as formerly thought, bringing hot masses to the
surface from the highly heated interior, but how can the heat of the
interior be barred against leakage and reduced to the relatively small
radiation emitted by the stars. "Smaller stars have to manufacture the
radiant heat which they emit, living from hand to mouth; the giant stars
merely leak radiant heat from their store."
So a radioactive type of equilibrium must be established, rather than a
convective one. Laboratory investigations of the very short waves are
now in progress, bearing on the transparency of stellar material to the
radiation traversing it; and the penetrating power of the star's
radiation is much like that of X-rays. The opacity is remarkably high,
explaining why the star is so nearly "heat-tight."
Opacity being constant, the total radiation of a giant star depends on
its mass only, and is quite independent of its temperature or state of
diffuseness. So that the total radiation of a star which is measured
roughly by its luminosity, may readily remain constant during the entire
'giant' stage of its history. As Russell originally pointed out, giant
stars of every spectral type have nearly the same luminosity. From the
range of luminosity of the giant stars, then, we may infer their range
of masses: they come out much alike, agreeing well with results obtained
by double-star investigation.
These studies of radiation and internal condition of the stars again
bring up the question of the original source of that supply of radiant
energy continually squandered by all self-luminous bodies. The giant
stars are especially prodigal, and radiate at least a hundredfold faster
than the sun.
"A star is drawing on some vast reservoir of energy," says Eddington,
"by means unknown to us. This reservoir can scarcely be other than the
sub-atomic energy which, it is known, exists abundantly in all matter;
we sometimes dream that man will one day learn how to release it and use
it for his service. The store is well-nigh inexhaustible, if only it
could be tapped. There is sufficient in the sun to maintain its output
of heat for fifteen billion years."
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Transcriber's Notes:
Obvious punctuation errors repaired. Hyphenation and spelling was
standardized by using the most prevalent form. The oe ligature was
converted to the letters "oe". Whole and fractional parts of numbers
are displayed as follows: 365-1/4.
Page Correction
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20 Aa => Aya
39 Ulugh Begh => Ulugh Beg
46 Instaurata Mecanica => Instauratae Mechanica
58 Oscillatorium Horologium => Horologium Oscillatorium
225 seceded => succeeded
226 areoplane => aeroplane
320 Plate 2 - Vulpeculae => Vulpecula
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