BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 559 



Hercchcl, W.: Syxopsis or the Wiutixgs of— Continued. 



A.D. Vol. P. 



liow necessary will it be to take notice of the fate of our neighbor- 

 ing suns in order to guess at that of our own. That star -which wo 

 call the Sun may to-morrow begin to undergo a gradual decay of 

 brightness, like /i Leonis, a Ceti, a Draconis, d Ursw Majoris, and 

 many others that will be mentioned in my catalogues. 



179G 8-') 18G It may suddenly increase like the wonderful star in the back of 

 Cassiopca^s chair, or gradually como on like fi dcminorum, fj Ccti, 

 C Sa<jUtaru, etc. ; or it may turn into a periodical star of 2.5 days' 

 duration, as Algol is one of 3 days, 5 Ccphci of 5 days, etc. 



186 Perhaps the easiest way of accounting for past changes in our cli- 



mates is to surmise that our sun has been formerly sometimes more 

 or sometimes less bright than now. 



187 A method of ascertamiug the quantity or intenseness of solar light 



might be contrived. Perhaps the thermometer alone might be suf- 

 ticieut. 

 187 Introductory Eemai-ks and Explanations of the Arrangement and Charac- 

 ters used in the following Catalogue. 

 This first catalogue contains 9 constellations; the rest will follow. 



190 All the observations have been made in very fine nights when there 



was no suspicion of any whitish haziness. 



191 All observations upon stars of any considerable magnitude have been 



made with the naked eye. 



191 Wherever I have used magnitudes I have adopted Flamsteed's scale. 



192 From the numerous differences wo have reason to suspect many 



changes in the lustre of stars since Flamsteed's time. 

 192 Summary of difierences with Flamsteed. 

 194 I. Catalogue of the comparative brightness of the Stars. 

 212 Notes. These contain errata in I'lamsteed's atlas and ca alogue. 

 226 Wm. IIeuschel. 



[Dated] Slough, near Windsor, Jan. 1, 1793. 



1796 8G 452 On the j)eriodical star a Uerculis ; with remarks tending to establish the 

 rotatory motion of the Stars on their axes. To which is added a second 

 catalogue of the comparative Brightness of the stars. By William 

 Heksciiel, LL. D., F. R. S. Read June 9, 1796. 



452 lu my first catalogue I announced a HercuVis as a periodical star. It 



has been compared with several standard stars but chicily with k 

 Ophiuchi. 



453 Table of the variation of light observed in a (Fl. 64) Ilereulls, com- 



pared to K (Fl. 27) Ophiuclii. 



454 The period is about GO days and a quarter. Greater accuracy can 



only be obtained by future observations. 



455 On the Botatory motion of the Stars on their Axes. 



455 We ought not to be satisfied with enrolling the discovery of one more 

 periodical star among the list of facts we are acquainted with ; for 

 this would indeed be of no great consequence. 



455 Darker spots on the surface of stars will account for all the phenomena 



of periodic stars so satisfactorily that we certainly need not look 

 out for any other cause. The objections which may bo made are: 

 the periods in Algol, [i Lyra, S Cephei, and rj Antinoi are short 3, 

 5,6, and 7, etc., days; those of o Ceti, the star in IJydra and in 

 Cygnus are long; 331, 394, and 497 days. 



456 Hitherto we have had but 7 periodical stars [some of very short, some 



