Abstract
THE ELLIPTICITY OF URANUS.—It may be remembered that Sir William Herschel, who was at first under the impression that the disk of Uranus presented a perfectly circular outline, was afterwards convinced that there was an appreciable elongation in the direction of the major-axis of the orbits of the satellites, though he has not recorded any measures to test this conclusion. On October 13, 1782, about eighteen months after the discovery of the planet, he writes: “I perceived no flattening of the polar regions.” On March 5, 1792, he used “a newly polished mirror of an excellent figure: it showed the planet very well defined and without any suspicion of a ring.” With powers 240–2400, all which his speculum bore with great distinctness, he formed a different opinion, and remarked, “I am pretty well convinced that the disk is flattened.” On February 26, 1794, he has an observation thus recorded, “20-feet reflector, power 480. The planet seems to be a little lengthened out in the direction of the longer axis of the satellites' orbits.” Further, in a paper communicated to the Royal Society in December, 1797, wherein he announces his supposed discovery of four additional satellites of Uranus, he says: “The flattening of the poles of the planet seems to be sufficiently ascertained by many observations. The 7-foot, 10-foot, and the 20-foot instruments equally confirm it, and the direction pointed out February 26, 1794, seems to be conformable to the analogies that may be drawn from the situation of the equator of Saturn and of Jupiter.” This ellipticity being admitted, he inferred that Uranus had a rapid axial rotation.
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Our Astronomical Column . Nature 28, 308 (1883). https://doi.org/10.1038/028308a0
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DOI: https://doi.org/10.1038/028308a0