Universe, SYSTEMS OF THE. —Universe (or world) is here taken in the astronomical sense, in its narrower or wider meanings, from our terrestrial planet to the stellar universe. The term "systems" restricts the view to the general structure and motions of the heavenly bodies, but comprises all the ages of the world, the present, past, and future.
I. HISTORIC TIMES OF THE UNIVERSE.—The present system, in the widest sense of the term, forms the subject of universal cosmography. Descriptions of this kind were made by Lambert, the two Herschels, Laplace, Newcomb, and others. The present section treats only of the solar system, and in particular of the disputed theories of Ptolemy and Copernicus, and the proofs in favor of the latter.
A. Ptolemaic and Copernican Systems.—(I) The earliest astronomical systems are found in the Greek school. No planetary system can be discerned in Chinese or Babylonian records. The astronomical knowledge of the Greeks shows three periods. Its infancy is represented by Philolaus and Eudoxus, of the fifth and fourth century B.C. The earth is the common center of the universe, within the celestial sphere of the fixed stars. The great luminaries, sun and moon, and the five planets have each their concentric spheres, upon which they slide in two directions, longitude and latitude, keeping constantly the same distance from the earth. The flourishing period of Greek astronomy extends from Heraclides Ponticus in the fourth century B.C. to Hipparchus in the second. Observation was made its basis. The different degrees of brilliancy observed in the nearest planets, Mercury, Venus, and Mars, at the times of the opposition and conjunction with the sun, pointed to heliocentric orbits, and analogy demanded the same arrangement for Jupiter and Saturn. The hypothesis was then established, probably by Heraclides himself, that the sun revolved annually, with the five planets, around the earth, while the moon remained on her sphere as before. Heraclides also made an important step in advance by asserting the diurnal rotation of the earth. His system was afterwards known as that of Tycho Brahe. Even the annual motion of the earth around the sun is mentioned by Heraclides as held by some of his contemporaries. The heliocentric system was certainly pronounced and defended by Aristarchus of Samos, although his writings are lost, and known only through Archimedes, whose works were published a year after Copernicus's death (Basle, 1544).
The period of decline had commenced when Hipparchus flashed up as the last genius among the Greek astronomers. The precession of the equinoxes, which he discovered, was made to fit the geocentric system, then prevailing, only a century after Aristarchus. The philosophical schools, in particular the Stoics, began to prefer astrology to observational astronomy. The geometrical knowledge that apparent or relative motion remains unaffected by an interchange of its component motions, as was correctly demonstrated by Apollonius, paved the way to the confusion of the solar system. It must be remembered that the apparent planetary motions are epicyclical, each planet revolving in its own orbit, the epicycle, around the sun, and with the sun, as center of the epicycle, apparently around the earth in a common orbit, which is called the deferent orbit. These are the correct ideas, and will ever form the basis of spherical astronomy.
The decadence of astronomical concepts among the Greek philosophers appeared in two ways. First, they applied the geometrical fiction of Apollonius to the physical planetary system, supposing that the epicycle must always be the smaller of the two components in apparent motion; and, secondly, they believed that a physical planet could revolve, all alone, around a fictitious point in space. For the outer planets, Mars, Jupiter, and Saturn, the apparent orbit of the sun is the smaller component—the common deferent orbit. It cannot be made the epicycle, with-out introducing into the system three new circles each with a fictitious center. This was done, but worse was to come for the inner planets, Venus and Mercury. There was no need for them to dislodge the common deferent circle, or solar orbit, as it was larger than the two planetary epicycles. And yet the center of the deferent was moved from the sun towards the earth, at the cost of introducing into the system two new circles and two ideal centers of motion. The precession of the equinoxes, discovered by Hipparchus, even lent support to the concept of fictitious pivots. It seemed to swing the pole of the ecliptic around the pole of the celestial sphere. In this shape the Greek system of the heavenly bodies came down to posterity, during the second century of our era, through Ptolemy's "Syntax". The two fundamental propositions of the geocentric system, viz. that the earth has no axial rotation and no translation in space, form the sixth chapter of the first book. The "Syntax" did not pass directly from the Alexandrian school to Europe. Greek astronomy made its round through Syria, Persia, and Tatary, under Albategnius, Ibn-Yunis, Ulugh-Beg. The Ptolemaic system was accepted by the Arabic astronomers without criticism, and was made known in Europe through their translations. An unintelligible Latin "Almagest" had taken the place of the Greek "Syntax", and rested like a tomb-stone on European astronomy.
(2) New astronomical life awoke in the fifteenth century in Germany. Nicholas of Cusa rejected the axioms of Ptolemy; Peurbach and Muller restored the text of Ptolemy's "Syntax", and Copernicus made it his life-work to disentangle the cycles and epicycles of the Greek system. The task of Copernicus was harder than that of his predecessor Aristarchus, on account of the unanimous acceptance of the geocentric system for more than a thousand years. The first book of Copernicus's great work, "On the Revolutions of the Celestial Bodies", is directed against the Ptolemaic axioms on the center of the universe and the stability of the earth. He rightly observes that the universe has no geometrical center. He then gives clear definitions of relative and apparent motion and applies the Apollonian principle of interchanging the component motions in the opposite sense of Ptolemy. The complex heavenly machinery was explained by a triple motion of the earth, one around its axis, another around the sun, and a third, a conical motion, around the axis of the ecliptic, in periods of respectively one day, one year, and 25,816 years. Ptolemy's negative arguments against a moving earth were answered in a masterly manner. It had been objected that a disastrous centrifugal force would be created on the surface of the earth. Copernicus retorts that a far greater centrifugal force must be admitted in the outer planets and the fixed stars if they revolved around the earth. The resistance of the atmosphere, which, it was urged, would sweep away every object from a moving earth, was disposed of by Copernicus, exactly as it is today: each planet condenses and carries its own atmosphere. A third difficulty was raised about necessary changes in the appearance of the constellations, or, in modern language, about large parallaxes of the stars, when viewed from opposite points of the earth's orbit. Copernicus correctly thought the stars so far away as to make the terrestrial orbit comparatively too small to show any effect in the instruments then available. The negative arguments of Ptolemy being dispelled, there remained only one positive argument, in favor of Copernicus.
(3) The simplicity of the heliocentric system had sufficient weight to convince a genius like Copernicus. He never called his system an hypothesis. The first who exercised censorship on the work "De revolutionibus" was the Reformer, Osiander. Dreading the opposition of the Wittenberg school, he put the word "Hypothesis" on the title-page and substituted for the preface of Copernicus one of his own—all with-out authorization. It was more than half a century later that the Congregation of the Index pointed out nine sentences that had either to be omitted or ex-pressed hypothetically before the book might be read freely by all. The argument of simplicity was greatly strengthened by Kepler, when he discovered the ellipticity of planetary orbits. Copernicus had found, by long years' observation, that the inequalities of planetary motion could not be accounted for, after Ptolemaic fashion, by simply placing the circular orbits excentrically. Not being prepared to abandon the circle, he resorted to small epicycles. Their final removal greatly enhanced the simplicity of the Copernican system. Then came the discoveries of the aberration of light and of stellar parallaxes. While they appeared as natural consequences of the orbital motion of the earth, they threw on the Ptolemaic system the condemnation of an almost infinite complexity. The fixed stars were recognized to vibrate in double ellipses, their major axes parallel to the ecliptic, in periods of exactly one year. The double ellipses are the images of the terrestrial orbit, projected on the celestial sphere by the parallactic displacement of the stars and by the finite velocity of light. The former kind is much the smaller of the two, and in most cases dwindles to immeasurable dimensions. Some twelve hundred of them have actually been observed. The aberration-ellipses have their apparent major axes all of equal length. The geocentric system not only has no explanation for these phenomena, but cannot even represent them without two epicycles for each star in the firmament. The Copernican argument of simplicity thereby received an overwhelming corroboration.
B. Direct Proofs of the Copernican System.—While the argument of greater simplicity is only an indirect criterion between the two opposing systems, mechanics has furnished more direct proofs. Copernicus actually had them in mind when he maintained that centrifugal force in a daily rotating celestial sphere would have to be enormous, that the atmosphere is condensed around the terrestrial globe, and that single planets cannot revolve around fictitious points that have no physical meaning. Kepler was too much preoccupied with geometrical studies and with the favorite idea of cosmical harmonics (Harmonices mundi) to recognize in the common focus of his elliptical orbits a governing power. It was reserved for Newton and Laplace to formulate the mechanical laws of celestial motion.
(I) The annual revolution of the earth around the sun is a necessary consequence of celestial mechanics. (a) Knowing the mathematical expression of centrifugal force, Newton computed, from the velocity and distance of our satellite, the amount of attraction that the earth must exercise upon it to maintain its orbital revolution. Learning then, from French geometers, the exact dimensions of the earth, he found the force that keeps the moon in her orbit to be identical with terrestrial gravity, divided by the square of the distance from the center. The discovery led to the computation of the masses of sun and planets, inclusive of the earth, the latter turning out more than three hundred thousand times lighter than the sun. The mechanical conclusion is that the lighter body revolves around the heavier, and not the reverse; or, in more scientific language, that both revolve around their common center of gravity, which, in this case, lies inside the solar sphere.
(b) Our satellite furnishes another more direct proof of the annual revolution of the earth. Carl Braun shows in the "Wochenschrift fur Astronomie", X (1867), 193, that the moon is attracted nearly three times more forcibly by the sun than by the earth. Our satellite would, therefore, leave us unless we revolved with it around the sun. The earth is only able to give the annual lunar orbit a serpentine shape, so as to have the satellite alternately outside and inside her own orbit.
(c) Newton also alludes to comets and shows that, in the Ptolemaic system, each of them needs an epicycle parallel to the ecliptic, to turn its orbit towards the sun. With our present cometary knowledge of comets the argument can be made stringent. More than three hundred comets have their orbits well determined. Over two hundred of them have passed the ecliptic within the earth's orbit, and some, like Halley's comet at its last appearance, almost in line between sun and earth. Most of the comets, including Halley's, come to us from distances beyond the orbit of Neptune. Now, computation shows that they all have their common focus in the sun and that the earth is, as a rule, outside their orbits. In the case of Halley's comet the earth was, at one time, even on the convex side of the orbit. The mechanical conclusion is as follows: If, without any regard to the earth, the comets obey the sun, the earth must do the same.
(2) The daily rotation of the earth around its axis is demonstrated in many ways. Once the annual revolution is proved, the daily rotation becomes a matter of course. If the earth has not the power to swing the sun around its own center once a year, it will be far less able to do so in one day; and if it cannot swing around one sun, what could it do with the countless suns of the universe? Yet, we have direct and special proofs of the diurnal rotation. They all rest on mechanics, partly celestial, partly terrestrial. Celestial mechanics has turned into proofs what formerly seemed to be difficulties. This occurred in the case of stellar parallaxes, the absence of which had been objected by Ptolemy, and the existence of which was shown by Bessel. The precession of the equinoxes also has changed its role. Laplace showed it to be due to the action of the sun on the protuberant equatorial regions of the rotating earth. The similar result of the action of the moon upon the earth is called nutation. Laplace's demonstration was based upon the flatness of the earth, which had been measured in the seventeenth century, and was also theoretically deduced by him from the existence of centrifugal force. We have here a complex reverse of roles. The consequences of centrifugal force, so strongly urged against diurnal rotation by Ptolemy, turned out to be the cause of precession, known to Hipparchus, and of several phenomena, discovered only after the time of Copernicus. Precession was still a matter of special difficulty to Copernicus, and the one of the three terrestrial motions that he could not explain. To him it was the resultant of two annual, slightly different, conical rotations of opposite direction, to which no cause could be assigned.
So much about the proofs from celestial mechanics. There are others, by means of instruments, so-called laboratory experiments. They commenced immediately after the time of Galilei and seem to have received the impulse from his trial. The experiments may be classified chronologically in five periods or groups. From 1640 to 1770 they were crude trials without result. The years from 1790 to 1831 were a period of experiments with falling bodies. The twenty years from 1832 to 1852 were a time of pendulum experiments. Then followed a period, 1852-80, of experiments with more elaborate apparatus; and the last, since 1902, may be called that of modern methods.
(a) The first period is represented by the names of Calignon, Mersenne, Viviani, and Newton. Calignon (1643) experimented with plumb lines, without knowing what their variations should tell. Mersenne (1643) had pieces of artillery directed to the zenith, rightly expecting a westerly deviation of the balls. Foucault's pendulum experiment was materially forestalled by Yiviani at Florence (1661) and Poleni at Padua (1742), but was not formally understood. The easterly deviation of falling bodies was explicitly announced by Newton, but unsuccessfully tried by Hooke (1680). Galilei had alluded to it before, in his "Dialogo" (Opere, VII, 1897), in a contradictory manner. In one place (p. 170) he denied the possibility of the experiment, in another (p. 259) he affirmed it. Lalande missed the opportunity of first making Newton's experiment at the Paris observatory. The honor was reserved to Abbate Guglielmini.
(b) The second period comprises the experiments with falling bodies, made by Guglielmini at Bologna (1790-2), by Benzenberg at Hamburg (1802) and Schlebusch (1804), and by Reich at Freiburg (1831). The general drift of the balls towards the east side of the meridian was unmistakable. It proved the rotation of the earth from west to east, but only in a qualitative manner. Quantitative proofs were obtained in the next period.
(c) Three kinds of pendulum experiments filled the third period. The horizontal pendulum was invented and tried by Hengler, in 1832, for the effects of the centrifugal force. The instrument is still waiting for a more delicate manipulator. Foucault's vertical pendulum dates from 1851, and was tried first in a cellar, then in the Paris Observatory, and last in the Pantheon. The deviation of the pendulum from the original vertical plane was clockwise, as expected by Foucault, but no quantitative measures were ever published by him. They were made in many places, chiefly in large cathedrals. The best results known are those of Secchi in Rome (1851) and of Garthe in Cologne (1852). Secchi experimented in San Ignazio, in presence of many Italian scientists, and Garthe in the cathedral, before Cardinal Geissel, royal princes, and numerous spectators. The counterproof in the southern hemisphere, where the deviation of the pendulum must be counter-clockwise, has not been made to this day. The attempt at Rio de Janeiro (1851) cannot be regarded as such. A conical pendulum was set in motion by Bravais in the same meridian room of the observatory and in the same year as the vertical pendulum of Foucault. The experiment had the advantage of being reversible. Swinging clockwise, the pendulum appeared to move faster than in the opposite sense, for the reason that the theodolite, in which it was observed, followed the rotation of the earth. Two pendulums used simultaneously, and moving in opposite directions, yielded the correct value of the diurnal rotation within a tenth of one per cent, a result never reached by Foucault's pendulum.
(d) The second half of the nineteenth century, the fourth period, is remarkable for complicated experiments and profound theories. The instruments were the gyroscope and the compound pendulum. The invention of the former is due to Foucault, and furnished a new proof of the diurnal rotation. It was constructed by him in three forms: the universal, the vertical, and the horizontal gyroscope, so called according to their degrees of freedom. The vertical gyroscope was perfected by Gilbert (1878) into his barogyroscope, while the horizontal gyroscope was lately introduced on warships as an astronomical compass. The proofs of Foucault and Gilbert could only be qualitative, for want of electric motors. The delicate experiment made in 1879 with the compound pendulum by Kamerlingh Onnes, comprises those of Foucault and Bravais as special cases, and in general all the movements between the plane and the circular pendulum vibrations (see "Specola Vaticana", I, 1911, Appendix 1).
(e) The fifth and last period of experiments falls within the twentieth century and presents no less than four proofs, all widely different among themselves. The difficult experiment with falling bodies was brought within the walls of the physical laboratory by E. H. Hall in 1902. Under improved facilities, a fall of only twenty-three meters showed the easterly deviation better than all the preceding trials with heights from three to seven times as large. In 1904 the gyroscope was made to yield quantitative results by Foppl. An electric motor gave to a double wheel of 160 pounds a speed of over two thousand turns a minute. The rotation of the earth was strong enough to deviate the horizontal axis, which was suspended on a triple wire, six and a half degrees from the prime-vertical. A novel scheme had been tried by Perrot in 1859. He made a liquid flow through the central orifice of a circular vessel, and rendered the currents visible by means of floating dust. We have to take his word, that the currents were spiral-shaped, and ran counter-clockwise. The experiment was repeated by Tumlirz in Vienna (1908), and its result photo-graphed and compared with theory. While the experiments of Hall, Foppl, and Tumlirz are repetitions of former ones, with improved methods, the next proof of the diurnal rotation is new as an experiment, although forecast in the idea by Poinsot as early as 1851. It was carried out at the Vatican Observatory in 1909. Its principle is that of equal areas described in equal times, applied to a horizontal beam suspended in form of a torsion balance, on which heavy masses can be moved. The shifting of the masses from extremity to center will make the beam turn faster than the earth; the opposite will happen in the reverse case. The last proof had never been proposed before, and consists in observing the thread of the Atwood machine in a telescope. Viewed in the meridian, the thread of the falling weight is seen to come down east of the plumb-line, but viewed in the prime vertical it remains exactly plumb. This experiment was likewise carried out at the Vatican Observatory in 1912 (see "Specola Vaticana", I, 1911, appendix II, 1912).
Some writers have expressed surprise that Catholic scientists were allowed to take part in the experiments, e.g. that Bonfioli, domestic prelate to Pius VI, assisted Guglielmini in measuring the impressions of the balls on the plate of wax (Benzenberg, "Umdrehung der Erde", 1804, 278), or that Secchi demonstrated the rotation of the earth in Rome "before all the people" (Wolf, "Handbuch", I, Zurich, 1890, no. 262 c). We must remember, however, that what was condemned in a former age was not the experiment but a then gratuitous assertion.
II. PAST AND FUTURE OF THE WORLD.—The present system of the world has been found, by the greatest scientists, to be in an unstable condition. As it is, it cannot have existed for many millions of years, nor can it last for many more. Naturally, therefore, speculations have arisen, both retrospective and prospective; but speculations they will remain. How the world has developed into its present shape, and how it will pass out of it, science will never tell. Cosmogony is the accepted name for all the hypotheses on the past (from kosmos, world, and gignesthai, to originate). A corresponding form from the Greek, to designate the speculations on the future of the world, cosmothany (world's death), was used by C. Braun (Kosmogonie, 1905, X, 346); more correct formations are perhaps: cosmophthory (phthora, corruption) or cosmodysy (dusis, occasus, decline). World must here be taken in all its narrower or wider meanings, as earth, solar system, stellar system, universe.
A. Cosmogony.—The writer of the article Cosmogony has well distinguished between mythical, Biblical, and scientific cosmogonies. While confining himself to the first kind, he left the second for the writer of Hexaemeron. and the third for the present article. The term "scientific" is used only for the sake of distinction. No cosmogony can really claim to be a scientific theory or even hypothesis, in the proper sense of a systematic development of the details from a definite number of assumed principles, after the manner of the long-accepted atomic theory, for example. All cosmogonies, so far imagined, have shared in the common fate of being refuted as insufficient or even impossible. Proposition and rejection are alike vague and uncertain, and must be so, as processes of extrapolation from laboratory laws to the fabric of the Creator. Cosmogonies may be classified according to the component parts of the word, considering either the various kinds of cosmos, or the variety of origins. The former classification will bring to light the necessity of some great cosmogony, while the latter will prove to be a mere enumeration of possibilities, real or imaginary.
(I) The classification of cosmogonies by worlds may begin with the microcosm of our terrestrial abode and end with the macrocosm of the universe.
(a) The structure of the earth points to a history, the chronological successions of which can be recognized, although the span of duration is unknown. The superficial layer, allotted to the human race, represents the "Quaternary age". Underlying in space, and preceding in time, there are three others, known as the recent formation, the cretaceous and jurassic formation, and finally the carboniferous and silurian. Parallel to the latter three ages, the tertiary, secondary, and primary, run the prehistoric ages of the biological kingdom, known as the cainozoic, the mesozoic, and the paleozoic. The mere aspect of the successive layers justifies their names and calls for a terrestrial cosmogony.
(b) No less explicit are the celestial indications of a planetary cosmogony. The five kinds of uniformity in the orbital motions of planets, satellites, and comets, adduced by Laplace, are not representative of modern cosmography. Laplace knew of only seven planets and eighteen satellites, while we can count eight major and some six hundred minor planets and twenty-six satellites. Besides smaller exceptions to Laplace's "uniformities", the singular situation of our own planet must be accentuated. The earth has only one moon, comparable to itself in size, while the inner planets are moonless, and the outer planets are accompanied by more numerous and more minute satellites, Neptune alone forming an apparent exception. The asteroidal and Saturnian rings render the difference between inner and outer planets still more conspicuous. The rapid discovery of puny satellites by photography has brought to light the asteroidal character of these bodies and suggests the conclusion, that the great planets are accompanied by zones of pigmy moonless, in direct and retrograde motion, in striking contrast to the earth-moon system. The latter forms a veritable binary system, the only one in the solar cortege. Far from destroying Laplace's conclusion, the variations and contrasts only confirm the belief in some planetary evolution. Whatever cosmogony may be imagined, it will have to account for the critical position occupied by our own planet.
(c) Terrestrial and planetary cosmogonies will not satisfy those who look up to systems of higher order, as they are called in Lambert's "Kosmologische Briefe" (1761). The solar system is a mere fragment of creation. Its fundamental plane, or ecliptic, is replaced in the stellar system by the galaxy, and its planetary revolutions have their equivalent in the proper motions of the stars, including our own sun, which is moving towards the constellation of Hercules. Even the difference between slow and swift planets is reflected in the white Helium-stars (6.5 kilometers per second) and the strongly colored stars (19.3 kilometers). The Jovian and Saturnian systems, with their client globes and rings, have their counter-parts in the solar clusters of the Pleiades and Hyades, drifting each of them along the galactic plane around some unknown center of gravity. The ecliptic character of the Milky Way is further evidenced by the grouping of the Algol stars and the nonce along its belt, representing stellar eclipses and collisions. The general condensation of the stars towards the galactic circle, and its lining by the brightest constellations in the heavens, has conveyed the idea of a flattened stellar cumulus. More likely its shape is that of a bipolar-spiral, judging from its branches and from two principal star-drifts in opposite directions. The vast system calls for an explanation of its origin: a stellar cosmogony. Here again, as in planetary cosmogony, our terrestrial home seems to present a singularity. Science urges the conclusion that one half of the stars, if not most of them, broke up into components as they condensed, a manner of evolution which would incapacitate them from becoming centers of planetary systems. Stellar cosmogony must leave the question open, whether the mechanism of our own system was not the outcome of special and peculiar design, fitting it to be the abode of life.
(d) Yet even the stellar agglomeration of the Milky Way is a tiny spot in the abysmal cosmos. From near its center, where we find ourselves at present, the heavens appear studded with similar groupings of masses, partly gaseous, partly condensed into fluid streams or solar clusters. Since Herschel gauged the heavens, more than thirteen thousand of these objects have been catalogued, and hundreds of thousands are suspected. Classifying them into diffused, spiral, and planetary nebulae, Herschel considered them as so many simultaneous exponents of gradual cosmic evolution, thus showing his belief in the possibility of some universal cosmogony. The belief has since been strengthened by a wider knowledge of the ultrasidereal world. Photography shows the heavens almost covered with nebulous matter, spectrum analysis reveals the general identity of comical elements, and has moreover disclosed the fact that planetary nebulae move at great speed with reference to the stellar system, while the diffused Orion nebula remains at rest. The necessity of some comprehensive cosmogony is apparent. Attempts in that direction have not been wanting, as we shall presently see.
(2) The classification of cosmogonies by the origin which they ascribe to the world, may appropriately rest on certain celestial objects, from which they took their inspiration. These are Saturn's rings, at first believed to be coherent masses, whether gaseous or fluid or solid; then the same rings as recognized (by Bond, 1851) to be a swarm of minute satellites; and finally the spiral nebula). The differences in the inspiring types led to corresponding differences in the predominant ideas of cosmogonists. Coherent rings demanded hydrodynamic treatment, pulverulent rings suggested meteoric theories, and spiral nebulae prompted ballistic speculations. Hydrodynamic cosmogonies confined themselves to the solar system; meteoric cosmogonies made faint attempts towards the stellar system, and only ballistic cosmogonies have dared to speculate on the undivided cosmos.
(a) First among the hydrodynamic cosmogonies is the "nebular hypothesis", imagined by Kant (1755), partly in contradiction with mechanical principles. The application of the hydrodynamic laws was reserved to Laplace (1798). His mechanism is too simple, however, for the complex problem. Objections were raised by Babinet (1861), Kirkwood (1869), Moulton (1900), and others. Roche (Montpellier, 1873) even fixed a limit for each primary planet, within which a liquid satellite could not revolve intact. Saturn's rings lying inside the limits, thus failed to accomplish what Kant and Laplace had expected. The field of cosmogonic possibilities was widened by Darwin and Poincare (1879-1885), when they introduced planetary tides, pear-shaped hydrodynamic surfaces and satellite fission; and again by C. Braun (1887-1905), when he pointed to plurality of condensation centers, to excentric collisions, and to the resultant effect between resisting medium and hydrostatic pressure. The applicability of Darwin's speculation to our lunar-terrestrial system, and to binary systems in general, has been questioned by Moulton.
(b) The bases of meteoric cosmogonies are the asteroidal composition of Saturn's rings and the affinity between meteors and comets, discovered by Schiaparelli. Meteors were no longer the debris of ruined worlds, they became the embryos. Nebulae, stars, comets, zodiac light, solar corona, all originated from meteoric clouds. Life was brought into the chaos of cosmic dust, cold and dark as it was from the first, by a devious variety of motions, after the fashion of Descartes's vortices, resulting in collisions, evaporations, condensations, and consequent production of heat. Suns were forming, Newton's gravitational law set in, and the masses began to comport themselves in the manner imagined by Laplace. Meteoric cosmogonies thus distinguished two periods: the Cartesian and the Newtonian. The quiet machinery of Laplace's annulation is preceded by a primeval whirlpool period. Representatives of meteoric cosmogony are Faye (1884), Lockyer (1887), and Ligondes (1897), while Kirkwood, Wolf, and Braun oppose it. Darwin tried to support it by applying the kinetic theory of gases to cosmic matter in meteoric condition, treating its particles as molecules on an enormously magnified scale. Belot (1911) has recently imagined a Cartesian whirlpool of cylindrical form, shooting like a torpedo into an amorphous nebular mass, in the direction of the solar apex. The effects of the impact on the cylinder are longitudinal vibrations with nodes, the embryos of the future planets.
(c) Ballistic cosmogonies take their pattern from nebulae. The spiral form of most nebulae, with interspersed nuclear condensations, opened the widest field for collision, ejection, and capture theories. Herschel did not venture on any hypothesis, although he believed in stellar growth from chaotic nebulous matter by a process through diffused spiral and planetary nebula). Even today science has not proved the transition from the nebular to the stellar condition of any celestial object. It is true, the bipolar structure of spiral nebulae, disclosed in recent years by photography, has greatly strengthened the idea of violent cosmogonic formations. Collision theories were propounded by Chamberlin and Moulton (1905) and by Arrhenius (1907). The process in a nebulae begins with nuclear condensations, which are followed by excentric collisions or disruptive approaches. Bipolar systems of streams are thus produced and, if combined with concurrent rotation, spiral nebulae are formed. Collisions are repeated on a smaller scale by the accretion of scattered material around denser nuclei. The further development partly overlaps with the hypothesis mentioned next.
An ejection theory is mentioned by Laplace, as due to Buff on, who supposed comets to fall into the sun and splash solar matter into space. A more scientific form is given to the theory by Wilde (1910). In the right and left spiral streams of nebulae, in their interspersed stellar condensations, and in the elongated fissions of their convolutions, he recognized processes like the eruption of solar protuberances, or the up-lifting of terrestrial continents, or the impacts attested by lunar craters. Planets and satellites are ejectamenta from exploded primaries. A capture theory was invented by See (1910). The parent of the solar system is a spiral nebula. Sun, planets, satellites, and comets originate from nuclear condensations, but their grouping into regular order is due to the capturing of the smaller by the larger. The out-lying wisps of the solar nebula appear as comets.
What precedes is more a classification than a description of the various cosmogonies. None of them has found universal acceptance, and none has escaped criticism.
B. Cosmodysy.—This is the proposed name for all the hypotheses on the future of the world, as explained in the introduction to section II. The literature on cosmodysy is far less extensive than that on cosmogony. The youth of the world seems to exert a stronger charm on human speculation than its old age and decline. There does not seem to exist any mythical cosmodysy, and very little can be found on scientific cosmodysies. So much the more explicit and detailed is Biblical cosmodysy (see Divine Judgment). And yet, from a scientific point of view, the prospective conclusion from the known premises of the present world would seem to be better warranted than retrospective speculations upon cosmical conditions entirely unknown. A classification of cosmodysies from the various meanings of cosmos would have no object, for want of scientific material. No terrestrial, planetary, stellar, or universal cosmodysies have been elaborated. Two classes, however, may be distinguished from the manner of end to which the world may come: the extinction and the destruction theories.
The extinction theory rests on a certain irreversible process, common to all natural phenomena. While the sum total of cosmical energy is supposed to remain constant, the amount of potential energy is steadily diminishing. It is the unstable condition of potential energy that animates all activity in the universe. Drifting as it is towards stability, it will end in exhaustion and repose. The process is not reversible and consequently not cyclical. Applying it to the earth but abstracting from organic life, it will mean the extinction of its interior plutonic power and of its rotary speed. The raising and shifting of continents, the continual tremors, occasional earth-quakes and volcanic eruptions, the gradual shrinkage of the crust and the wandering of the polar ice caps, are so many irretrievable losses of potential energy. If the lengthening of our time scale, the sidereal day, is not directly observable, it is at least indicated in the apparent acceleration of the moon's longitudinal motions, and theoretically assured from the oceanic elevation, always east of the moon and acting as a perennial brake on the revolving globe.
The stability of planetary movements is guaranteed only for the span of historic times. The demonstrations given by Lagrange, Laplace, Poisson, Delaunay, Gylden, all rest on successive approximation, and, what is worse, they are based on fictitious celestial points and Newtonian attraction, exclusive of resisting medium, planetary tides, magnetic fields, and radio-repulsive forces. The resisting medium alone would suffice to change planetary orbits into spirals with the sun as the final pole and resting-place. Our sun is not exempt from the general thermodynamic process. Its temperature is constantly sinking, and all theories of complete contemporaneous compensation, by contraction and meteoric impacts, have been rejected. According to Lord Kelvin, the sun has not illuminated the earth for five hundred millions of years, and will not do so for many millions of years longer, unless new sources are discovered in the storehouse of creation. The recent electronic theory of matter has indeed complicated the problem of elemental evolution, but, so far, has not reversed the general process towards repose. May not the extinction of our luminary be forecast by the multitudinous existence of obscure stars, ascertained by Bessel and confirmed by the spectroscope?
The destruction theory does not consider annihilation of matter; it only opens the field of perturbations in the present organization of planetary or stellar systems. Within the solar system, the erratic procedure of comets and meteors is harmless only because of their insignificance. In a sidereal cluster, like the Milky Way, however, star may collide with star, or star with cosmic cloud. The spectacle of meteors, kindling to brief splendor in shooting athwart our atmosphere, is repeated on an enormous scale in the blazing stars that occasionally appear in nebula or clusters, particularly in the Milky Way. Rising in a few days to a thousand times their normal brilliancy, they relapse in the course of years into their former obscurity. Temporary stars were known to Hipparchus and gave the impulse to his star catalogue. From 1848 to the time when the continuous photographic survey of the heavens began, about one in ten years was noticed with the naked eye. At present, novice are announced almost every year; but, like the shooting stars, most will pass unnoticed. Whether the stellar conflagration is due to direct collision, or the passing of stars within grazing distance, or rather to the shooting of globes through cosmical clouds or nebulae, in all cases it would mean the end of our terrestrial habitation. The orbit of our sun is inclined at a small angle to the plane of the Milky Way, and its pace is little more than half the average stellar speed. This is all we know of our cosmic tour. Will the sun forever keep clear of the star throngs, and never get entangled in the diffused nebulosities with which the Milky Way abounds? Small as our knowledge is of the stellar agglomeration in which we travel, it dwindles to almost nothing in regard to ultra-galactic worlds. Whether they are embryos or ruins will be an enigma forever. We can only say that, if spiral nebulae develop into galaxies, the incessant action of their clustering power must produce conditions for catastrophes, at least similar to those we are witnessing in the Milky Way.
Our scanty science of cosmodysy might be a temptation to look for further information in the Scripture. Will the darkening of sun and moon, and the falling of stars, lend support to the extinction theory? Or does St. Peter advocate the destruction theory when he speaks of the heavens being on fire and the elements melted by burning heat? The like question may be raised in cosmogony. Can Genesis be consulted to decide between the hydrodynamic, the meteoric, and the ballistic hypotheses? The answer is given by an attempt, made three centuries ago, in cosmography. The Scriptural decision of the controversy, whether the solar system be geocentric or heliocentric, was bound to be a failure either way. Cosmogonic revelation was given to impress on the human race its physical and moral dependency upon the Creator. Likewise has cosmodysic revelation the purpose of holding out to mankind the final administration of justice. Purely scientific curiosity will find no satisfaction in Scripture.
J. G. HAGEN