148 SPECIAL RESULTS IN THE URANOLOGICAL 



three phenomena are probably intimately allied. The new 

 star in Cygnus (1600), which, after entirely disappearing, 

 (to the unassisted eye, it must be remembered), reappeared 

 and remained as a star of the 6th magnitude, leads us to 

 recognise the affinity between the two first kinds of celestial 

 phenomena. The celebrated Tychonian star of 1572 was 

 believed, while its light still shone, to be identical with the 

 new star of 945 and ]264. The period of 300 years sur- 

 mised by Goodricke (the intervals between the epochs of the 

 phenomena, which are perhaps not very certain, are 319 and 

 308 years), is reduced by Keill and Pigott to 150 years. 

 Arago ( 271 ) has shewn how improbable it is that Tycho Brahe's 

 star (1572) should belong to the class of periodically varying 

 stars. Nothing as yet would appear to justify our regarding 

 all newly appeared stars as variable in periods of long, and 

 therefore unknown, duration. If, for example, we regard the 

 self-luminosity of all the suns in the firmament as the 

 results of electro-magnetic processes in their respective 

 photospheres, we may (without assuming local and tem- 

 porary condensations of the " celestial air," or the intervention 

 of cosmical clouds) imagine this luminous process to take 

 place in various manners, either once only or periodically, 

 and either regularly or irregularly in respect to the time of 

 recurrence. The electric luminous processes of our ter- 

 restrial globe, whether presenting themselves to us as thunder- 

 storms in the atmosphere, or as polar effluxes, with much 

 seemingly irregular variability, do yet often shew also a 

 certain periodicity dependent on the seasons of the year and 

 the hours of the day. We may even often trace this peri- 

 odicity in the formation, for several successive days, and in 

 an otherwise perfectly serene sky, of small clouds at the same 



