184 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 39 



characteristic of various other known elements. But there were 

 two lines noted in the green that evaded identification, and the 

 elusive matter that emitted light of those particular wave-lengths 

 resisted all attempts made by astrophysicists to pin a label to it. 

 These unidentified lines were later found in the spectra of many 

 of the gaseous nebulae and, with improved instrumental power 

 coupled with photography, similar unidentified lines were also found 

 and ascribed to the same mystery element. The strong pair of lines 

 in the green portion of the spectrum have been designated N^ and N2, 

 their wave lengths being A 4959 and A 5007. There is another line 

 A 4363; yet another close pair occurs in the ultraviolet end of the 

 spectrum. 



The nineteenth century astronomers originally assumed that these 

 lines were the hallmark of an element which had not then been dis- 

 covered terrestrially. In fact it was given the atomic weight "three" 

 in the scale of the elements, and was named nebulium — the gas of the 

 nebulae. As one writer put it, "The recognition mark of nebulium 

 is a vivid green ray by the emission of which it is known to have a 

 concrete existence." 



Afterward, the question arose as to whether this green shining 

 gas, this "element" that had cropped up so unexpectedly in outer 

 space, was really something that had evaded chemical discovery on 

 earth. Was it something more primitive? It must be confessed 

 that, in many cases, speculation overrode sound scientific method, 

 and it was suggested in several quarters, and by good authorities, 

 that this celestial radiance might be due to the primeval protyle 

 or "world-stuff," the cosmic protoplasmic fluid from which the uni- 

 verse had been manufactured in the beginning. Indeed, Professor 

 Stokes went so far as to state, "It may possibly indicate some form 

 of matter more elementary than we know on earth * * *" 



However, the investigation of nebulium continued, and as new 

 elements were discovered, so were their emission spectra lines 

 matched with those of nebulium. But to no purpose. None were 

 found to coincide. The gaps in the table of elements became fewer 

 and fewer; hope began to fade. It gradually came to be accepted 

 that the hypothetical nebulium was some familiar gas clothed in an 

 unfamiliar fashion. 



And so it proved. This assumption was made, and the problem 

 strongly attacked by Dr. Wright at the Lick Observatory. The 

 assault was continued by I. S. Bowen, and nebulium began to shed 

 its cloak of mystery. Bowen, in 1927, showed by the use of modern 

 atomic theory, and by elegant mathematical reasoning, that first, 

 the lines of nebulium were of the variety that require a huge amount 

 of energy for their excitation. Second, the gas must be in a high 



