Variable Stars. 



Si 



meteoric matter was vigorously proceeding — say an undeveloped 

 sun — were to produce enough light by these innumerable and inces- 

 sant collisions to become visible to us as an embryo star; then 

 suppose a meteor swarm of large proportions, not yet condensed 

 into a visible planet, were revolving about the meteoric star in a 

 long elliptical orbit like a comet, and that at its perihelion passage 

 of the nebulous star, it should approach so close as to pass through 

 a portion of the outlying, sparsely diffused, uncondensed nebula : 

 the result would be a great temp rary increase of collisions and 

 consequently of light, given forth by the incipient sun. After the 

 perihelion passage of ihe uncondensed planer, the light would 

 recede, of course, to its Former intensity. 



For it should be observed that not only do stars exhibit marked 

 changes in brilliancy, but man)- instances are recorded where those 

 intangible objects known as true nebulae have mysteriously appeared, 

 shore forth with steady unmistakable lustre for a time, and then 

 have dwindled away or utterly vanished from the ken of the most 

 powerful telescopes. 



But though some nebuhe have newly dawned upon the vision, 

 and others have entirely faded from view, and still others are under- 

 going perceptible changes of form and of brightness, there is no 

 recorded instance of a nebula exhibiting any periodical changes in 

 light. Variable stars are numerous, but variable nebula with 

 periodic fluctuations of light are as yet unknown. 



