EVOLUTION IN THE SUNS 65 



spectra in the case of most metals become 

 entirely changed, showing that a new stage 

 in the disintegration of the metal has been 

 reached. For example, the iron arc-spectrum 

 of the voltaic arc contains some thousands of 

 lines, as if the iron atom might be regarded 

 almost as a planet which by the agency of the 

 intense heat of the arc had been split into 

 thousands of meteorites. But at the conditions 

 of the vacuum spark spectrum, these thousands 

 of lines have disappeared, and become re- 

 placed by a few much more strongly marked 

 lines, three of which are especially characteris- 

 tic. These lines, from their strength and their 

 persistence in greater intensity when the others 

 have disappeared, are called the " enhanced " 

 lines of iron. Now, apart altogether from 

 stellar spectroscopy, this series of changes 

 in the lines of a metallic spectrum most 

 strongly indicates, if indeed it does not 

 prove, a corresponding change in the ele- 

 mental constitution of the metal while under 

 the energy-environment of the air-arc or 

 spark-gap respectively, and it will presently be 

 seen that under energy conditions which we 

 cannot at present attain upon earth, even the 

 spark-spectrum of certain metals disappears 

 at certain levels, showing still more complete 

 disruption. The many-lined arc spectrum 



