ASTRONOMY.
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could not even see it with the help of a glass-. Maruldi and Cas-sini, after repeated observations, determined its period to be 403days, and M. le Gentil 405-pc days. This last astronomer an-nounced the times of this states greatest splendor to the end of the18th century ; but Mr. Pigolt has observed it at its greatest lustretwo mouths later than according to the table of M. le Gentil,namely, the 9 th of July 1783, the 4th of August 17S4, and the 1 stof September J 78A ; and he supposes its period to be only 390days, and 21 hours, ( PkiL Trans. 1786.) These returns are sub-ject to physical inequalities; for in the years 1699 , 1700, and1701, it was hardly visible, even at the times in which, accordingto the observations of the preceding and following years, it wasexpected to be at its greatest splendor.’ It is sometimes as brightas the s m the neck ol the Swan, which is of the third magnitude.'The second changeable star in the Swan is near the y,which is uponthe breast; it w as discovered in 1600 by Janson. Mr. Pigottthinks that the period of its disappearance is every 18 years. Ithas been observed of the third magnitude, though Mr. Pigott neversaw it brighter than the sixth. Its mean right ascension on Sept.
1 , 1782, was 302° 26 '45". The third variable star in the Swan,which now- has ceased to appear, was discovered by P. Anthelmcon June 20 , 1670, near the head of the Swan, on the side of thewing, who then saw it of the third magnitude; but the 10 th ofAugust following it was not brighter than the fifth magnitude, andsoon afterwards entirely disappeared. Its longitude was ™ 1°55',and latitude 47° 28'north. P. Anthelme saw it again March 17,1671, and estimated it of the fourth magnitude. Domin. Cassini,in that year, remarked in it great variations; it was twice at its greatestsplendor, viz. the 4th of April and beginning of May. In 1672,it was seen again of the sixth magnitude, but has not appearedsince. The celebrated M. Montanari, professor of Mathematicsin the university of Bononia, in his letter to the Royal Society ,dated April 30, 1670 , writes thus: “ There are now wanting in theheavens two stars of the second magnitude, in the stern of the shipArgo, and its yard. Barents marked them with the letters y3 andy . I and others observed them in the year 1664, upon the occa-sion of the comet that appeared that year. When they disappearediirst I know not, only I am sure that in the year 1668, upon the10th of April, there was not the least glimpse of them to be seen ;and yet the rest about them, even of the third and fourth magni-tudes, remained the same. I have observed many more changesamong the fixed stars, even to the number of a hundred, thoughnone of them are so great as those I have shewed.” Domin. Cas-sini observed a star of the fourth magnitude, and two of the fifth,in the constellation of Cassiopeia , in the places where it is probablenone were ever seen before. In 1671, Cassini discovered fivenew' stars iu Cassiopeia , three of which have since disappeared.This great astronomer also saw, near the boundary of the constel-lation of the river Eridanus, two new stars, one of the fourth andthe other of the fifth magnitude. It is certain that these couldnot have appeared till after A. D. 1664, for had they beenpreviously visible, they must undoubtedly have been seen,as the passage of a comet at that time through this part ofthe heavens was the occasion of all the stars in or about its pathbeing carefully examined. He also found four stars of the fifth orsixth magnitude near the north pole, where, he thinks, astrono-mers, who often observe this part of the heavens, must haveseen them, if they had before been visible. The star whichBuyer placed near the t of the Little Bear has disappeared, ashad also that in Andromeda, which is marked A; but this latter re-appeared in 1693. Instead of that which is marked -j in the kneeof Andromeda, there have appeared two others a little to thenorth of it. The star f in Andromeda has faded very much, inlustre. The star which 'Tycho Brahe placed at the extremity ofthe chain of Andromeda, as being of the fifth magnitude, became,in the time of Domin. Cassini, so very faint as scarcely to be vi-sible. Maraldi also discovered several variations in the appear-ances of the fixed stars ; of which an account is given in the His-toire de l’Academie lor the year 1695. The star * in the left legof Sagittarius is marked by Bayer of the third magnitude ; but in1671 it appeared only of the sixth. Dr. Halley saw it in 1676,ef the third magnitude, but it was hardly visible in 1692 ; and in1693 and 1694 lie saw it of the fourth magnitude. Maruldi alsofound in the same constellation several stars whose apparent mag-nitudes were widely ditferent from those noted down in the celes-tial charts. The star in the right arm of Sagittarius, which Halley
had marked of the third magnitude appeared to him much fainter.That which was upon his thigh, marked 9 by Bayer, had disap-peared. Maraldi first saw it in 1699, of the sixth magnitude; andabout this place he observed in 1709 two stars, which differedabout 33' in latitude. 'The same kind of variation has been no-ticed in the tail of the Serpent 0, which Tycho and Bayer had-found of the third magnitude, but which Montanari had judged ofthe fifth, and which has become somewhat brighter in the lollow-mg years. Several variable stars have also been seen in Serpentavius,which have afterwards totally disappeared; an instance of whichis that one in the preceding foot of this constellation, marked j byBa er, which has not appeared since the time of Montanari. 'l ivestar 4 . in the Lion was seen in 1667 by Montanari, which from thetime of Ty ho had not entirely become invisible, but when Ma-raldi observed it in 1691, it had then become very faint. Thestar| in the Lion, which was marked bv Tycho and Bayer of thefourth magnitude, Maraldi says, was scarcely visible in 1693; andthe star 2 of the sixth magnitude, in the breast of the Lion entirely disappeared in 1709. The head of Medusa , Algol, or £of Perseus , was observed by Montanari of different magnitudes atdifferent times. Maraldi perceived very little variation in it in1693; but in 1694, it increased and decreased in lustre consider-ably, appearing sometimes of the second, and at other times of thethird and fourth magnitude. A very particular account of this staris given under the article Ai.goi.. 'The star y which is in the rightear of the Dog, was marked by Tycho and Bayer of the third mag-nitude ; but in 1670 it was no longer visible, according to Mon-tanari : anil in 1692 and 1693 it appeared as a star of the fourthmagnitude. Maraldi discovered, in 1704, a variable star in theconstellation of Hydra of the fourth magnitude. It had then13h. 18m. of right ascension, and 22° 10' of south declination.He saw it several times till 1712; since which time it had beenthought to have inlirely disappeared; but Mr. Pigott found itagain, and observed its greatest splendor on Jan. 26, 1784, andMay 27, 1783. He has also determined its period of variation tohe 494 days. T he star /3 in the Eagle, which at the time of Bayerwas b righter than the y, since he assigned it the next place after there, is now much fainter than the y, and is scarcely of the fourthmagnitude. The /5 of the Whale is brighter than the re ; as is alsothe /3 in Gemini than the The re of the Dragon which Flam-steed and Bradley marked of the second magnitude, is now only ofthe fourth ; the <r in Sagittarius is also brighter than the w, and, inthe opinion of Dr. Herscheland M. Schon, its lustre varies periodi-cally. 'The preceding star * in the left leg of Sagittarius, which wasmarked by Bayer ot the third magnitude, appeared in 1671 onlyof the sixth. In 1676 it was somewhat brighter, and Halleymarked it of the third magnitude. In 1692 Maraldi could scarcelyperceive it; but in 1693 and 1694, it was of the fourth magnitude.Mr. Goodricke remarked in 1784, that the star /S in the Harp , de-creases from the third to the fifth magnitude every 6d. 9jh. Mr.Pigott, in 1785, has also found that the star >1 in Antinous , hasa periodical variation in 7d. 4 vh. It at one time varies from thethird to the fourth magnitude, and at another from the fourth to(he fifth. Mr. Wurm lias found its period to be 7d. 5-jrh. which is1 | hour greater than that of Mr. Goodricke. The*-in the con-stellation of Ceplieus varies from the third to the fifth magnitudeevery 5d. 8 h. 37m. According to Mr. Goodricke it was betweenits greatest and least lustre on Aug. 31, 1786, at noon. It is some-times fainter, and sometimes brighter than the f. It is extremelydifficult for us to determine with any degree of certainty whateverthe cause of the various changes of light in many of the fixed stars,and many very wild and uncouth conjectures on this head, havebeen presented to the public by different authors. Neither canwc subscribe to the opinion of the celebrated M. de la Place, whenhe says to the following effect, that “ the extensive spots whichthese fixed stars present to us periodically in turning 011 their ownaxes, nearly in the same manner as the last satellite of Saturn, andthe interposition of large opaque bodies which.circulate round,them, are sufficient to explain the periodical variations of thechangeable stars. As to those stars, (he adds,) w hich suddenly appearwith a most brilliant light, and then vanish, it may be supposedKith great probability, that great conflagrations, occasioned byextraordinary causes, take place on their surface, and this suppo-sition is confirmed by tiieir change of colour, analogous to thatwhich is presented to us on the Earth by bodies w hich are con-sumed bv fire.”
(208.) All