THE SPECTRA OF STARS AND NEBULA. 



27 



white or bluish stars, such as Sirius or Vega, here were supplemented 

 by a sec< nid series interpolated between them, and the establishment 

 of the significance of the relationship of the two series has been 

 partly Professor Fowler's work. 



A research of enthralling interest has been carried out within the 

 last few years by Professsor Nicholson, and the work is still being 

 carried on. If we may so express it, he has been constructing 

 artificial elements in his study ; that is to say he has been computing 

 the spectrum which an atom of a given type of structure would 

 yield. In this way he has been able to show that lines in the 

 spectra of nebulae, of the sun's corona, and of certain peculiar stars 

 generally known from the names of their discoverers as Wolf-Ka vet, 

 are typical of elements more simple in structure than any with 

 which we are acquainted in our laboratories. The structure of 

 such an atom may be imagined by likening it to a sort of solar 

 system in the infinitesimal. Pound a sphere of positive electricity 

 of relatively great mass a few electrons of negative charge but very 

 small mass revolve rapidly ; it is from their vibrations that the lines 

 of the spectrum proceed. Thus the rainbow has given us a clue as 

 to the most intimate structure of elements, some of which we have 

 never yet met with on our own planet. 



Colonel Mackinlay had great pleasure in seconding the vote of 

 thanks to Professor Fowler. There was one question which he would 

 like to ask Professor Fowler. It was well known that there were 

 some double stars of which one was visible to us and the other 

 invisible ; would it be possible to get the spectrum of the invisible 

 star ? 



Professor Fowler said that it was possible to detect the move- 

 ments of stars in the line of sight by the displacement of the lines 

 in their spectra, and in that way, in some cases, they had obtained 

 evidence of the existence of non-luminous stars in association with 

 visible stars. It was theoretically possible that such a non-luminous 

 star might be hot enough to produce some thermal effect, to yield 

 a spectrum in the invisible region in the infra-red, and such 

 spectrum might give traces of absorption. At present, however, 

 this was an excursion into the realms of romance ; it was not within 

 our present powers. 



Mr. Sutton proposed a hearty vote of thanks to the Astronomer 

 Royal for presiding that afternoon. They had heard that afternoon 



