Fantasy Football Challenge - Football Fanatics Library

Fantasy Football Challenge - Library of Books for Football Fanatics

Fantasy Football Challenge presents
Popular Science Monthly

75 of 119

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

75 of 119 pages. Go to page:

Go to this Book's Directory Page