620 SCIENCE PROGRESS 



Dr. Adams has found an interesting relation between the average 

 displacements of the dark absorptions in the four stars Nova 

 Aurigae (1892), Nova Persei (1901), Nova Geminorum (1912), 

 and Nova Aquilae (191 8), the four brightest discovered in recent 

 years. " We find," he writes/ " the surprising result that the 

 displacements of the lines in all those stars are directly pro- 

 portional to wave-length, and divide themselves into two pairs 

 of equal amount. Of these the first pair of stars has exactly 

 twice the displacement of the second, and it is perhaps a 

 significant fact that Nova Aquilae and Nova Persei were much 

 brighter stars apparently, and probably intrinsically as well, 

 than Nova Geminorum and Nova Aurigse." He also finds, in 

 the case of Nova Aquilae, a progressive displacement of the 

 absorptions at successive dates, the average daily increase in 

 displacement between June 10 and June 15 being slightly over 

 a half unit of wave-length. Mr. Evershed had also recorded 

 the same phenomenon for the hydrogen absorptions. This 

 progressive increase in velocity is also observed in solar promi- 

 nences, and furnishes another bond of union between the solar 

 outbursts and the sudden appearance of new stars.' 



The next phase in the progression of spectra in a new star 

 is the gradual dying out of the bright bands, characteristic of 

 an a Cygni or solar chromospheric type, and their replacement 

 by bright bands which are represented in helium stars, such 

 as 7 Orionis. The helium is accompanied by oxygen and 

 nitrogen. Meanwhile a bright band near wave-length 4640, a 

 composite band, which is seen in the very early stages of the 

 star's spectrum, grows brighter and brighter, until it becomes 

 one of the brightest bands in the spectrum. This band has 

 been unravelled by Dr. Lunt,' who shows that it contains high- 

 temperature nitrogen. His conclusions have been corrobo- 

 rated by Prof. Fowler * from laboratory researches. Besides 

 nitrogen, the band contains carbon, which can be obtained in 

 a laboratory only by very heavy electrical discharges, and 

 helium. This composite band is of great importance in new 

 stars, for it links up all the successive phases of its radiative 

 activity. The B type of spectrum, or spectrum like 7 Orionis, 

 gradually, in its turn, gives place to the spectrum of a planetary 

 nebula. In this spectrum the radiations at wave-lengths 5007 



^ Proceedings National Academy of Science, iv. 355. 



* In the case of Nova Cygni (1920) Dr. Lockyer has made the interesting 

 observation that the variable velocity curve of the dark hydrogen is the 

 counterpart of the light curve. The velocity varied from 330 kilometres 

 per second on August 22 to a maximum of 900 on August 26, and then were 

 gradually reduced to 460 by September ig. {Monthly Notices, R.A.S., 

 Ixxxi. 46.) 



^ Monthly Notices, R.A.S., Ixxx. 534. 



* Ibid., Ixxx, 692. 



