132 SPECIAL RESULTS IN THE URANOLOGICAL PORTION 



IV. 



NEWLY- APPEARED AND VANISHED STARS. VARIABLE STARS, 



WHICH HAVE MEASURED AND RECURRING PERIODS. 



VARIATIONS OF THE INTENSITY OF LIGHT IN CELESTIAL 

 BODIES OF WHICH THE PERIODICITY HAS NOT YET BEEN 

 INVESTIGATED. 



THE appearance of previously unseen stars in the celestial 

 vault, especially the sudden appearance of strongly scin 

 tillating stars of the 1st magnitude, is an event in the 

 regions of space of which the occurrence has ever ex- 

 cited the astonishment of men. This astonishment is so 

 much the greater, as such an event in Nature as the 

 sudden visibility of an object which, though previously 

 unseen, we yet believe to have existed previously, is one of 

 the rarest of all phsenomena. In the course of the three 

 centuries from 1500 to 1800, there have appeared to the 

 inhabitants of the northern hemisphere 42 comets visible 

 to the naked eye, being, on an average, 14 in a century ; 

 while, during the same three hundred years, only 8 new stars 

 have been observed. The rarity of the latter occurrence 

 becomes still more striking when we embrace yet longer 

 periods. From the important epoch in the history of 

 astronomy of the completion of the Alphonsine Tables, to 

 the time of William Herschel, or from 1252 to 1800, we 



