VAEIABLE STARS ROBINSON 131 



Arguments against the theory are also serious and difficult to meet. 

 About the only alternative left for the fission theory proponent is to 

 ask: What are the ancestors of this class of binary stars? Equally 

 well may one ask the same question with regard to all double star 

 systems. For the visual and telescopic doubles, however, the above 

 conditions are neither necessary nor sufficient, and by no one is any 

 relationship claimed between these stars and any class of variables. 



In our own galactic system the total number of known variable 

 stars given by the 1932 edition of Prager's catalogue is 5,461, about 

 a large percentage of which nothing is loiown. A relatively large 

 percentage of the remainder belongs to classes of irregular or semi- 

 regular stars which may be intermediate between the various classes 

 of periodic variables. We know practically nothing about these 

 stars, since they demand series of observations more continuous than 

 those now available. It is quite possible also that continuous series 

 of observations made on all classes of variables would shed much 

 light on the peculiarities and the causes of their variations which 

 have hitherto escaped our attention. 



Not only the professional astronomer but the amateur, likewise, 

 can assist in answering astronomical questions. The part of the 

 amateur astronomer is most strikingly manifested by the great work 

 of the American Association of Variable Star Observers, composed 

 of about 350 members working in this country and abroad, who in 

 the course of a year report more than 25,000 observations on vari- 

 able stars to its recorder, Mr. Leon Campbell, of Harvard College 

 Observatory. By this organization more than a third of a million 

 observations have been made on 500 variable stars, mostly of long 

 period, and for the peculiar variable SS Cygni not a single maxi- 

 mum brightness during the last 35 years has escaped their notice. 

 Besides this enormous program, a huge amount of variable star work 

 is done at Harvard College Observatory by temporary employees 

 who have other lines of activity and who do not claim to be profes- 

 sional astronomers. The field is a large one, and thus far we believe 

 that we have done little more than penetrate the surfaces of the 

 associated problems. 

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