THE NEW STAR WHICH FADED INTO STAR-MIST. 123 



sphere of a star, consisting of incandescent gases, as is 

 the case with our own sun, is on the whole cooler than the 

 nucleus, but with regard to the latter is extremely large. 

 I cannot well imagine how the phenomenon can last for 

 any long period of time if the former hypothesis be correct. 

 The gas breaking forth from the hot interior of the body 

 will impart a portion of its heat to the surface of the body, 

 and thus raise the temperature of the latter ; consequently, 

 the difference of temperature between the incandescent 

 gas and the surface of the body will soon be insufficient 

 to produce bright lines; and these will disappear from 

 the spectrum. This view applies perfectly to stars which 

 suddenly appear and soon disappear again, or at least 

 increase considerably in intensity that is, it applies per- 

 fectly to so-called new stars in the spectra of which bright 

 lines are apparent, if the hypothesis presently to be 

 mentioned is admitted for their explanation. For a more 

 stable state of things the second hypothesis seems to be 

 far better adapted. Stars like Beta Lyrae, Gamma Cas 

 siopeise, and others, which show the hydrogen lines and the 

 sierra D line bright on a continuous spectrum, with only 

 slight changes of intensity, possess, according to this theory, 

 atmospheres very large relatively to their own volume 

 the atmospheres consisting of hydrogen and that unknown 

 element which produces the D line.* With regard to the 

 new star, Zollner, long before the progress lately made in 

 stellar physics by means of spectrum analysis, deduced from 

 Tycho's observations of the star called after him, that on 

 the surface of a star, through the constant emission of heat, 

 the products of cooling, which in the case of our sun we call 

 sun-spots, accumulate : so that finally the whole surface of 

 the body is covered with a colder stratum, which gives 



* The D line, properly speaking, as originally named by Fraun- 

 hofer, belongs to sodium. The line spoken of above as the sierra 

 D line is one close by the sodium line, and mistaken for it when 

 first seen in the spectrum of the coloured prominences as a bright 

 line. It does not appear as a dark line in the solar spectrum. 



