204 COSMOS. 



IV. 



NEW STARS AND STARS THAT HAVE VANISHED. VARIABLE 

 STARS, WHOSE RECURRING PERIODS HAVE BEEN DETER- 

 MINED. VARIATIONS IN THE INTENSITY OF THE LIGHT 

 OF STARS WHOSE PERIODICITY IS AS YET TJNINVESTI- 

 GATED. 



NEW STARS. The appearance of hitherto unseen stars in 

 the vault of heaven, especially the sudden appearance of 

 strongly scintillating stars of the first magnitude, is an 

 occurrence in the realms of space which has ever excited 

 astonishment. This astonishment is the greater, in propor- 

 tion as such an event as the sudden manifestation of what 

 was before invisible, but which nevertheless is supposed 

 to have previously existed, is one of the very rarest phe- 

 nomena in nature. While in the three centuries from 

 1500 to 1800, as many as forty- two comets, visible to 

 the naked eye, have appeared to the inhabitants of the 

 northern hemisphere on an average, fourteen in every 

 hundred years only eight new stars have been observed 

 throughout the same period. The rarity of the latter be- 

 comes still more striking, when we extend our consideration 

 to yet longer periods. From the completion of the Alphonsine 

 tables, an important epoch in the history of astronomy, down 

 to the time of William Herschel that is, from 1252 to 

 1800 the number of visible comets is estimated at about 

 sixty-three, while that of new stars does not amount to more 

 than nine. Consequently, for the period during which, in the 

 civilized countries of Europe, we may depend on possessing 

 a tolerably correct enumeration of both, the proportion of 

 new stars to comets visible to the naked eye is as one to 



