Image from page 296 of "Astronomy for the use of schools and academies" (1882)
Publisher: New York : Potter, Ainsworth, & Co.
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress
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ng. Struve, in 1851, advanced the startling theory that the inneredge of the ring was gradually approaching the planet, the ASTRONOMY. 269 whole ring spreading inwards, and making the central openingsmaller. The theory was based upon the descriptions anddrawings of the rings by the astronomers of the seventeenthcentury, especially Huyghens, and the measures made by laterastronomers up to 1851. This supposed change in the dimen-sion of the ring is shown in Fig. 300. 274. Constitution of Saturns Ring. — The theory now gen-erally held by astronomers is, that the ring is composed of acloud of satellites too small to be separately seen in the tele-scope, and too close together to admit of visible intervalsbetween them. The ring looks solid, because its parts aretco small and too numerous to be seen singly. They are likethe minute drops of water that make up clouds and fogs,which to our eyes seem like solid masses. In the dusky ringthe particles may be so scattered that we can see through
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Fig. 300. the cloud, the duskiness being due to the blending of light anddarkness. Some believe, however, that the duskiness is causedby the darker color of the particles rather than by their beingfarther apart. Uranus. 275. Orbit and Dimensions of Uranus. — Uranus, thesmallest of the outer group of planets, has a diameter ofnearly thirty-two thousand miles. It is a little less densethan Jupiter, and its mean distance from the sun is aboutseventeen hundred and seventy millions of miles. Its orbithas about the same eccentricity as that of Jupiter, and isinclined less than a degree to the ecliptic. Uranus makes 270 ASTRONOMY.
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