Abstract
MANCHESTER. Literary and Philosophical Society, October 4.—Mr. Francis Jones, president, in the chair.—T. Thorp: A method for preventing the tarnishing of silver-on-glass parabolic mirrors. The mirror was carefully levelled on a turntable, and its axis of rotation made coincident with that o'f the turntable. The whole was then rotated uniformly at the calculated speed required to cause a liquid to assume the same parabolic form as that of the mirror. A i per cent, solution of “Schering's” celloiditve in amyl acetate (after a lengthy period of settling) was flooded on to the surface of the mirror to a depth of about one-third of a millimetre. This was allowed to dry very slowly, when the resultant film was found to have a perfectly even surface of a thickness of about 1/300th of a millimetre. On testing the mirror no perceptible loss of definition was observed, and in actual use the performance was satisfactory. It is absolutely essential for the success of the method that the mirror be quite enclosed, and exposed only to an atmosphere of amyl acetate so as not to be allowed to dry, for about one hour after the solution has been flooded on, as, without this precaution, a perfectly uniform film cannot be obtained.—Dr. Henry Wilde: The origin of cometary bodies and Saturn's rings. The first part of this paper is a further exposition of the author's theory of the origin of comets and cometary bodies from the interior of the planets of the solar system, with new illustrations drawn from experimental mechanics. Dr. Wilde considers that the recently discovered satellites of Jupiter and Saturn, which have retrograde motions, are planetary ejectamenta, and from their comparative minuteness are hardly entitled to rank as satellites. The theory advanced by Olbers, the illustrious discoverer of Pallas and Vesta, that the planetoids are fragments of an exploded planet, finds confirmation in the great irregularities of their orbits and the direct and retrograde motions of cometary bodies. The author next discussed the origin of Saturn's rings, which has for a long time engaged the attention of. natural philosophers. Kant assumed that Saturn at an early period of its history had the characteristics of a comet, and that its tails contracted upon the planet and formed a ring. Laplace supposed the rings to be the original nebular substance uncondensed into the form of a satellite. The author ventures to affirm that the rings ate the ejectamenta of Saturn when its diminishing energies were insufficient to eject a comet with its train of meteorites, or a cometary satellite. Dr. Wilde adduced evidence to show that the interior rings were formed some time subsequently to the outermost one, which is separated from the others by an annular space of 2585 miles. The author has drawn up a table of distances of the rings from Saturn and the times of their revolutions, calculated from his measurements of the photographs recently taken at the Lick Observatory.
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Societies and Academies . Nature 84, 521–522 (1910). https://doi.org/10.1038/084521b0
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DOI: https://doi.org/10.1038/084521b0