X THE STARRY HEAVENS 419 



the " fiery Dogstar," as it used to be, is 

 now, and has been for centuries, a clear 

 white. 



The star known as Nova Cygni — the "new 

 star in the Constellation of the Swan" — was 

 first observed on the 24th November 1876 by 

 Dr. Schmidt of Athens, who had examined 

 that part of the heavens only four days before, 

 and is sure that no such star was visible then. 

 At its brightest it was a brilliant star of the 

 third magnitude, but this only lasted for a 

 few days ; in a week it had ceased to be a 

 conspicuous object, and in a fortnight became 

 invisible without -a telescope. Its sudden 

 splendour was probably due to a collision be- 

 tween two bodies, and was probably little, if 

 at all, less than that of the Sun itself. It is 

 still a mystery how so great a conflagration 

 can have diminished so rapidly. 



But though we speak of some stars as 

 specially variable, they are no doubt all un- 

 dergoing slow change. There was a time 

 when they were not, and one will come when 

 they will cease to shine. Each, indeed, has a 

 life-history of its own. Some, doubtless, rep- 



