TRANSACTIONS OF THE SECTIONS. 37 



appearance of the now well-known variable Mira Ceti, and the Dutch Professor 

 Holwarda, who discovered its periodicity, the list of observers of these objects includes 

 most of the greatest names that have figured in astronomy : — Hcvelius, Bulliald, 

 Montanari, Cassini, Maraldi, G. and C. Kirch, Ilalley, Koch, Goodricke, and 

 Pigott — all contributed largely by discovery or observation to our knowledge of the 

 variable stars. Sir William Ilerschcl's first astronomical communications were 

 upon the same subject, since most ably followed up by Sir John Ilerschel, the 

 distinguished inheritor of his great name and lofty talents. Olbers paid great 

 attention to the variable stars, as also Harding, Wurm, Westphal, Schwerd, and 

 above all others, Professor Argelander, of Bonn. To him is due not merely the 

 merit of arranging the labours of all that had preceded him, and more accurately 

 investigating the elements of change of most of the old variables, as well as the 

 discovery of several new ones, but that of training a band of young and able followers, 

 who by their successive discoveries and patient researches have honoured both 

 themselves and their great instructor. In England, besides the labours of Sir John 

 Herschel, Mr. Hind has discovered no less than twenty-one new telescopic variable 

 stars, two of which, S Cancri and U Geminorum, are especially remarkable. The 

 writer of this paper has also contributed ten to the list, which now numbers more 

 than eighty of these interesting objects. Mr. Baxendell of Manchester, Messrs 

 Chacornac and Goldschmidt of Paris, as well as Drs. Winnecke, Schoenfeld, Luther, 

 Auvers, Hoek, Oudemans, and Schmidt, are all devoting more or less of their time 

 and attention to the same pursuit. 



Why then, it may be inquired, have not all these combined efforts proved as suc- 

 cessful as they undoubtedly deserved to be, in arriving at more satisfactory results? 

 We can only regret the circumstance, and redouble our exertions to attain so important 

 an object. Want of continuity is doubtless a most weighty objection to all pre- 

 viously published series of observations, and one which the observers could not help : 

 for unless a star be circumpolar, there must inevitably occur a break in the records 

 of its changes during the time that it is in conjunction with the sun, and therefore 

 not observable. It is not enough merely to watch a star through its successive 

 maxima ; every stage of its variation should be remarked, and an unbroken record 

 thereof kept for years, or at least through ten or twelve complete periods. The 

 detection of four remarkably regular variable stars, suitably placed in the circumpolar 

 region, has enabled me to secure this desideratum, and to supply data not previously 

 available. 



A brief summary of the principal features hitherto remarked in periodical stars, 

 maybe advantageously stated, before proceeding to the description of our illustrations. 

 Some of them, from fine bright stars distinctly visible to the naked eye, fade away 

 heyond the limits ofthe largest telescopes in use, and after remaining invisible a 

 certain time suddenly regain their brilliancy. The increase in light is generally 

 more rapid than the diminution, and about or after maximum such stars are frequently 

 more or less red. Others, usually of short period and small variation, complete their 

 changes in a few hours, and at all intermediate stages are of a constant magnitude. 

 Most ofthe stars of this class are visible to the naked eye and pretty steady in their 

 periods, which may be stated as between the limits, three and forty-six days; while 

 those of the former class, or vanishing stars, range from 97 to 650 days in the 

 interval between two successive maxima. In one instance the period cannot be less 

 than seventy-three years ; and it is even probable that some ofthe brilliant visitors, 

 described as new or temporary stars in past ages, may be periodical, but returning 

 only after the lapse of many centuries. 



The largest of our three diagrams represents the light curve, or graphic history, of 

 the circumpolar variable star R Ursae Majoris, since 1853, the year of discovery of 

 its variability. Eight maxima, dependent upon 138 observations, and seven minima, 

 resting upon 122 observations, making in all 260 nights on which the star has 

 been examined, are here presented to the view. The Time co-ordinates, marked 

 along the top and bottom ofthe projection, are on a scale of ten days to an inch. 

 The other co-ordinate — magnitude or light — is marked at each extremity of the dia- 

 gram. The upper limit, which, however, this star has never attained, is the 6th 

 magnitude, or faintest visible to the unassisted sight. The lower limit is 13*, or the 

 faintest magnitude discernible with a telescope of 7 inches in aperture. The 



