OCR Text |
Show JUPITER. <br><br> Jupiter's diameter is about 11 times that of our earth, and his mean density is about a quarter of that of the earth, or about a third more than water. Now, a bulky body may be composed of heavy materials, and still, as a whole, be light, like an iron ship or a lump of pumice stone, that will float in water. The pumice lump is light on account of its vesicular formation, so that the mass consists of heavy felspathic material and the air it contains. Extract the air, and the pumice loses it floating power, though still far from heavy in proportion to its bulk. Most of the earth's crust is formed of solids much heavier than water. Granites are more than two and a half times heavier than water, slaty rocks about the same, and so are ordinary lime-stones, the variations from all being about 2.5 to 2.9. The ironstone group contains denser minerals; red hematite has a specific gravity of 4.5, magnetic ironstone, 4.5 to 5.2, etc., and many other ores are heavy. At some remote period, when only part of the now solid earth had been condensed from gaseous and vapory matter, our planet might have had a mean density like that of Jupiter, as its rocky materials contain between 10 and 50 per cent of oxygen; and while condensations and chemical combinations were going on rapidly our globe must have been the scene of "Thunders, lightnings, and prodigious storms." And it is probable that certain stars which have suddenly blazed forth with passing splendor have exhibited to us the spectacle of conflagrations extending over millions and billions of square miles. Color changes in Jupiter - such as those noticed by Mr. Browning and the writer in 1800, '70 - may have been caused by soda flames, though not fierce enough or extensive enough to add materially to his ordinary luminosity, which is estimated as always exceeding, though not in a very high degree, what it would be by mere reflection of light received from the sun. - Belgravia. |