IN STARRY SKIES

Evening Post, Volume CXII, Issue 97, 21 October 1926, Page 19

IN STARRY SKIES

THE SUCCESSORS OF LAPLACE

PROCTOR, LOCKYER, CHAMBER LIN, AND MOULTON

(By "Omega Centauri.")

When it became evident that the solar system could never have originated exactly in the manner described by Laplace, many modifications of the Ne- ; bular Hypothesis were made. The first was concerned with temperature. It is difficult to imagine a gas of such extreme tenuity as that of the original nebula to be intensely heated. Further, it seems unnecessary to make any such Supposition since heat must be produced by the contraction oi' the nebula. In some modern theories, therefore, the primitive nebula is cold. But one of the most puzzling problems of astronomy is the maintenance of the sun's energy during vast periods.. The complete answer has not yet been given, though, perhaps, Eddington and Jeans are approximating to it. But the search for an explanation led to a fuller recognition of the cosmical importance of meteorites. The position, fifty years ago, "was gummed up by Proctor when he pointed out that for uncounted ages two great processes had been at work supplementing the solar store of energy, namely, the contraction of- its mass from a nebulous condition and the fall of innumerable millions of minute cosmical bodies upon its surface. Although these two can account for but a small fraction of the perennial output, some portion of the sun's energy is certainly derived from each. Helmholtz, Mayer, ana Kelvin made this quite clear, and they even made numerical estimates of the respective contributions. The total, • however, proved quite inadequate to satisfy the! geologists. The search, though not completely successful, had revealed the astonishing abundance of meteoric matteY within the solar system. Sir Norman Lockyer was greatly impressed with the importance of the part which this material might play in the processes of cosmical evolution. After a quarter of a century of study and Tesearch he became convinced of the meteoric origin of the sun. Balfour Stewart had suggested many years before that sunspots were produced by the fall of bodies upon the unn's surface. Lockyer pointed out that this was not necessarily meteoric action from without, for incandescent iron vapour is certainly an important constituent of the sun's atmosphere, and | iust as we have snow and ram and hail, ) so the sun must be bombarded by iron snow, iron rain, and iron hail. Bnt undoubtedly meteorites from more distant space do also reach the .sun s surface. It has been estimated that twenty million a day enter the earth s atmosphere, and the. meteoric harvest of the earth must be an insignificant fraction of that of the sun. Lockyel recognised that meteoric action accounted for very many other phenomena besides those of the snn. He developed a wide and far-reaching meteoric^ hypothesis. In this, instead of ■■ vast mass of hot gas as the original state of sun or star, he took an immense swarm of cold meteorites. He did not explain the origin of this meteoric swarm, but relied on the abundant evidence of the presence of innumerable meteorites in the space traversed by the earth. Nebulae, even those whose spectra of bright lines show the presence of luminous gas, were held by Mm to be meteoric swarms. The meteorites themselves, being cold and solid, gave no light. The gases were liberated by their collisions. Lockyer maintained that the closest possible connection exists between stars and nebulae; that they are just two stages in a single evolution series. Many bodies that look like stars are simply the centres of nebulous meteoric swarms. Variable stars he considered to be double. swarms moving in elliptic orbits round their common centre of gravity, and partly penetrating one another, at their nearest approach. New stars he accounted for by the clash of swarms that tried to pass one another on parabolic or hyperbolic orbits. One outstanding truth which Lockyer was one of the first to recognise is that stars are not all falling in temperature. There is an ascending as well as a descending series. Our sun is one of those whose temperature is falling. For many years Lockyer was almost alone in upholding this opinion, but when it was put on a firmer footing as the theory of giants and dwarfs by Hertzsprung and Eussell, it was universally accepted. Lockyer continually tested his theories by experiment.1 In the laboratory he exposed meteorites to different temperatures, such as those of the bunsen name, the electric arc, and the electric spark. He compared the spectra produced under these conditions with the spectra of comets and of nebulae. He concluded that both of these are meteoric swarms. When meteorites are heated the occluded gases, chiefly hydrogen, the cleveite gases and carbon compounds are first given off. As the temperature rises, these are followed by metallic vapours. Similar spectra may result in the light from meteoric swams through the gases and vapours being liberated by collisions and perhaps rendered luminous by electrical excitation. Lockyer considered the phenomena of Novae and variable stars in great detail, but did not discuss fully the peculiarities of the solar system. Ho was convinced, however, that it had its origin in a nebula which was not completely gaseous, but contained some gases amongst its constituents. |As long ago as 1878, a theory was published, which up to the present appears capable of explaining the peculiarities of the solar system more completely than any other, and yet is comparatively unknown. This is the Encounter Theory of Professor Bickerton. Amongst the reasons for its being overlooked are the facts that it waa enunciated hy a professor of chemistry and physics, not by an astronomer, and that it was published in the Transactions of the New Zealand Institute,: which deal chiefly with- biology. Before considering this theory let us fpilow the trend of thought on the subject in the astronomical world of Europe and America. Probably the best known of all recent theories, aS to the origin of the Solar System, is the planetesimal hypothesis of Chambcrlin and Moulton. These authors recognised, as do all scientists of the present day, that "the order of yesterday changed into that of torday in a lawful and continuous manner, and the order of to-day will go over into that of to-morrow continually and systematically." They discarded the hot gaseous nebula of Laplace and postulated something more like the meteoric swarms of Proctor and Lockyer. The remote ancestor of our system is pictured by them as a more or less condensed and well-defined central sun, having slow rotation and surrounded by a vast swarm of somewhat irregularly scattered secondary bodies, or planetesimals. Their theory is, in ono respect, a groat advance on that of Laplace. They try to explain the distribution of the material in the primitive system. Whether we can agree with their explanation or not is quite a different matter. But an explanation, though open to criticism, ie better than no explanation at all. According to the planetesimal hypothesis, at a time

when our Sun was much larger and far less dense than it is now, another, and probably a larger, star passed near to it. If it came within ten or five million miles the tide raising forces due to it would be two thousand to sixteen thousand times as great as those oi the Moon or the Earth., According to the density of the Sun at the time, these tides would be between 500 and several thousand miles high. The authors of the hypothesis point out further that the sun is subject to violent explosive forces which eject the matter, which forms eruptive prominences, to distances of several hundred thousand miles. Whilst. the .disturbing star was passing, they consider that the ejections would reach far greater dimensions and be thrown much farther. They picture two diametrically opposite tongues of fire drawn or projected from 'she Sun and, by the attraction of the passing star, deflected into orbits round the solar nucleus. This gives the first glimpse of planets. The nucleus of the system is now surrounded by a vast swarm of planetesimals. They move approximately in the original plane of relative motion of the Sun and the star. They all revolve in the same direction because of "the pull of the passing star, but each follows an essentially independent elliptic orbit. Amongst these planete>imals are nuclei which become centres of condensation, and in the course of their revolutions sweep up the smaller planetesimals and gradually grow into planets. The satellites are supposed to originate from secondary nuclei which must have been associated with the primary ones from the beginning. They also grow in i"ass by sweeping" up planetesimals. This theory, .of which we have given but a meagre outline, has been developed in considerable detail by its authors. As Moulton says: "The importance of a general principle is proportional to the number of known facts it correlates." The theory deserves close examination from this point of view, and it should be compared and contrasted with its rivals.