624 SCIENCE PROGRESS 



a shooting star in the earth's atmosphere. But there are plenty 

 of nebulae not in the Milky Way, though not so many gaseous 

 nebulae, and there are plenty of moving stars. Why, if the 

 supposition is correct, are the new stars confined to the Milky 

 Way ? 



We have endeavoured to state the conditions, as derived 

 from observation, of the problem that awaits solution. Some- 

 how, at first, an explosive outburst of a solar type is involved, 

 and finally a planetary nebula. How ? In his extensive study 

 of Nova Geminorum II (1912), recently published,^ Lieutenant- 

 Colonel Stratton gives as his opinion that the best solution 

 available at present is " the spreading out of streamers of 

 glowing gases from a central body after a collision with a 

 quiescent dark cloud, and the final formation of a planetary 

 nebula with a Wolf-Rayet star as nucleus." Of prime impor- 

 tance is his discovery that the absorption spectrum can be 

 analysed in terms of the stronger lines of two typical spectra, 

 a Cygni and 7 Orionis, and that the displacement of these two 

 spectra, which varies from day to day, is widely different for the 

 two groups of elements involved in the two typical spectra. 



^ Annals of the Solar Physics Observatory, Cambridge, vol. iv, part i. 



