560 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Herscliel, W.: Synopsis of the Writings of— Continued. 



A.D. Vol. P. 



of very long periods]; the discovery of a Herculis as a periodical 

 star with a period of GO days supplies a link in the chain and re- 

 moves the objection that arose from the vacancy. 



1796 8G 456 Another instance of slow rotation is the .5th satellite of Saturn IJape- 



tiis'\, which revolves on its axis in 79 days. 

 457 The rotations of the sun, moon, and some of the planets are known 

 by their spots ; [t/a^jeias] is too small and too distant to allow its spots 

 to be observed. But what we can no longer perceive we can now 

 supply by rational arguments. The change in the light of the satel- 

 lite proves the rotation ; the rotation proves the existence of the 

 spots. A still more extended similarity between the sun and the 

 stars offers itself, by the spots which must also be admitted to take 

 place. 



457 There are reasons to surmise that 34 Cygni is a periodical star of 18 



years' rettirn [see Phil. Trans., 1786, p. 201]. 



458 When the biography of the stars, if I may be allowed the expression, 



is arrived to more perfection, wo may then possibly not only be still 

 more assured of their rotatory motion, but also perceive that they 

 have other movements, such as nutations of their axes, etc. 



458 Memorandum relating to the following Catalogue. I find tbo magnitudes 



of Flamsteed so inconsistent that I shall not continue to note tko 

 deviations between my observations and his. 



459 II. Catalogue of the comparative brightness of the Stars. 

 477 Xotes. 



Wm. Herschel. 

 [Dated] Slough near Windsor, June 1, 1796. 



1797 87 293 A Third Catalogtie of the comparative Brightness of the Stars ; with an in- 



troductory account of an Index to Mr. Flamsteed's Observations of the 

 Fixed Stars contained in the second volume of the Historia Calesfis. 

 To which are added several useful 7-esults derived from that Index. By 

 William Herschel, LL. D., F. R. S. Read May 18, 1797. 



293 In my earliest reviews of the heaveus I found many of the stars of 



the British Catalogue missing, and took it for granted that they 

 were lost. The deviation of many stars from the magnitudes there 

 given I looked upon as changes in the lustre of the stars. I there- 

 fore wished to be able to refer to the original observations upon 

 which the Catalogue was founded, and recommended to my sister 

 the arduous task. 



294 She began the work about 20 months ago, and has lately finished 



it. 



294 Description of the manner of making the index. 



295 Examjiles of its use. 



296 General results to be obtained from an inspection of the index [with 



regard to Flamsteed's errors]. 



297 Additional notes to the stars in the First Catalogue of the comparative bright- 



ness of the Stars. 

 301 Same for the Second Catalogue. 



307 III. Catalogue of the comparative brightness of the Stars. 

 321 Notes. 



Wm. Herschel. 

 324 [Dated] Slough, near Windsor, April 12, 1797. 



