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owe its existence to the blue flare some months previous, which 

 had taken that time to traverse the huge distances separating 

 the outlying portions from the centre. If this be so, we may 

 further suspect the nebula of having been concerned in some 

 way in the original outburst. It seems plausible that some 

 kind of encounter between the previously faint star and the 

 previously faint nebula should have resulted in a great develop- 

 ment of heat and light which sent the news to us. 



It would be interesting to get confirmation of this possibility 

 in other cases, but unfortunately the conditions are not always 

 so favourable. Nova Persei blazed up brighter than the first 

 magnitude stars, and though there have been New Stars even 

 brighter than these (such as that of 1572 which was even visible 

 in the daytime), most of those we now find are much less bright; 

 so that if they are accompanied by the illumination of nebulae 

 our resources are not able to photograph them. 



Here we must conclude this brief review of a quarter of a 

 century's work on the Great Star Map and other matters related 

 to it. The work is far from concluded as a whole, though two 

 portions of it have been so far finished as to enable us to form 

 some idea of the completed whole. But the attainment of any 

 particular stage is after all only an incident in a journey, for in 

 a very real sense the map will never be finished. Our real 

 concern is not with the state of the heavens at any particular 

 moment but with the changes which may be discerned by 

 comparing one epoch with another ; accordingly when we have 

 mapped out any region satisfactorily we are not at the end but 

 at the beginning. Our real work "consists in watching the 

 development of change, which may be slow to declare itself to 

 our brief lives but will persist relentlessly during eternity. 



