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 438 ASTRONOMY. rays near its middle, is liable to feveral clianges, and-is pafted Sirius in brightnefs and magnitude ; and was feeh fometimes invifible. Another is near the eclipticj be- for 16 months fucceffively. At firft it appeared bigger tween the head and bow of Sagittarius it is fmall, but than Jupiter to fome eyes, by which it was feen at midvery luminous. A third is on the back of the Centaur, day : afterwards it decayed gradually both in magnitude which is too far fouth to be feen in Britain. A fourth, and luftre, until Mkrch 1573, when it became invifible. of a fmaller fize, is before Antihous’s right foot; having On the 13th of Auguft 1596, David Fabricius oba dan in it, which makes it appear more bright. A fifth ferved the Stella Mira, or wonderful ftar, in the neck is in the conitellation of Hercules, between; the ftars £ of the Whale ; which has been fince found to appear and and n, which fpot, though but fmall, is vlfible to the difappear periodically, feven times in fix years, contibare eye, if the ficy be clear and the moon abfent. nuing in the greateft luftre for 15 days together ; and is Cloudy Jlars are fo called from their mifly appearance. never quite extinguifhed. They look like dim ftars to the naked eye -; but through In the year 1600, William Janfenius difcovered a a telefcope they appear broad illuminated parts of the changeable ftar in the neck of the Swan ; which, in time, Iky ; in fome of which is one ftar, in others more.- Five became fo fmall as to be thought to difappear entirely, of thefe are mentioned'by Ptolemy, i. One at the ex- till the years 1657, 1658, and 1659, when it recovered tremity of the right hand of Perfeus. 2. One in thd its former luftre and magnitude ; but foon decayed, and middle of the Crab. 3. One unformed, near the !fting is now of the final left fize. of the Scorpion. 4. The eye of Sagittarius. 5. One In the year 1604 Kepler and feveral of his friends faw in the head of Orion. In the firft of thefe appear more a new ftar near the heel of the right foot of Serpentaftars through the telefcope than in any of the reft, al- rius, fo bright and fparkling, that it exceeded any thing though 21 have been counted in the head of Orion, and they had ever feen before ; and took notice that it was above 40 in that of the Crab. Two are vifible in the every moment changing into fome of the colours of the eye of Sagittarius without a telefcope, and feveral more rainbow, except when it was near the horizon, at which with it. Flamfteed obferved a cloudy ftar in the bow of time it was generally white. It furpaffed Jupiter in magSagittarius, containing many fmall ftars ; and the ftar d nitude, which was near it all the month of Oftober, but above Sagittarius’s right (boulder is encompafled with . eafily diftinguifhed from Jupiter, by the fteady light of feveral more. Both Caffini and Flamfteed difcovered Jupiter. It difappeared between O&ober 1605 and one between the Great and Little Dog, which is very the February following, and has not been feen fince that full of ftars vifible only by the teleicope. The two time. whitilh fpots near the fouth pole, called the Magellanic In the year 1670, July 15, Hevelius difcovered a new Clouds by Sailors, which to die bare eye refemble part ftar, which in Odlober was fo decayed as to be fcarce of the Milky Way, appear through telefcopes to be a perceptible. In April following it regained its luftre, mixture of fmall clouds and ttars. But the moft re- but wholly difappeared in Auguft. In March 1672 it markable of all the cloudy ftars is that in the middle of was feen. again, but very fmall; and has not been vifible Orion’s Sword, where feven ftars (of which three are fince. very clofe together) feem tolhine through a cloud, very In the year 1686 a new ftar was difcovered by Kirch, lucid near the middle, but faint and ill defined about the which returns periodically in 404 days. edges. It looks like a gap in the (ley, through which In the year 1672, Caffini faw a ftar in the neck of the one may fee (as it were) part of a much brighter re- Bull, which he thought was not vifible in Tycho’s time, gion. Although moft of thefe fpaces are but a few mi- nor when Bayer made his figures. nutes of a degree in breadth, yet, fince they are among Many ftars, befides thofe above mentioned, have been the fixed ftars, they muft be fpaces larger than what is obferved to change their magnitudes : and as none of occupied by our folar fyftem ; and in which there feems them could ever be perceived to have tails, it is plain to be a perpetual uninterrupted day among numberlefs they could not be comets ; efpecially as they had no parallax, even when largeft and brighteft. It would feem, worlds, which no human art ever can difeover. Several ftars are mentioned by ancient aftronomers, that the periodical ftars have vaft clufters of dark fpots, which are not now to be found ; and others are now vi- and very flow rotations on their axes ; by which means, fible- to the hare eye which are not recorded in the ancient they muft difappear when the fide covered with fpots is catalogues. Hipparphus obferved a new ftar about 120 turned towards us. And as for thofe which break out years before Chrift ; but he has not mentioned in what all of a fudden with fuch luftre, it is by no means impart of the heaven it was feen, although it occafioned probable that they are funs whofe fuel is almoft fpent, his making a catalogue of the ftars ; which is the moft and again fupplied by fome of their comets falling upon them, and occafioning an uncommon blaze and fplendor ancient that we have. The iirft new ftar that we have any good account of, for fome time ; which indeed appears to be the greateft was difcovered by Cornelius Gemma on the 8th of No- ufe of the cometary part of any fyftem Some vember^. D. 1572, in the chair of Caffiopea. It fur# M. Maupsrtuis, in his dijfertation on the figures of the celeflial bodies, (p. 61,—63is of opinion that fomefiars, by their prodigious quick rotations on their axes, may not only affurne the figures of oblate fpheroids, but that, by the great centrifugal force arifmg from fuch notations, they may becom* of the figures of mill-ftones