Page:Popular Science Monthly Volume 15.djvu/12

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THE POPULAR SCIENCE MONTHLY.

shape, not only by diurnal motion, but by the more potent influence arising from the attraction of a great central orb, similar results may be obtained, but they admit of a more obvious explanation. The accompanying figure will give an idea of the manner in which, in such dangerous ground, a secondary planet would be affected, especially if it were composed of homogeneous and very yielding materials. If the two bodies were as disproportionate in size as Jupiter and his nearest moon, stability would be impossible on the minor one as soon as gravity

PSM V15 D012 Gravitational pull on an orbiting object.jpg

at the extremities of its longest diameter was reduced more than fifty per cent, by the disturbances. Of the fatal effects of a further reduction adequate proofs are afforded by three different modes of investigation which I have given in the "Philosophical Magazine" for 1860, 1861, and 1871. Accordingly, on coming into fatal proximity with its primary, such a satellite would not lose its matter in small portions, but would pass away in one great convulsion which would destroy the planetary condition and give birth to a ring.

The insecurity which analysis shows in this case in the mundane structure arises from the circumstance that, when gravity is reduced to less than one half its value along the greatest axis, the pressure along that line can no longer be made to counterpoise the pressure from other