d 



18 



in the relative intensities of the lines were due to 

 a reduced temperature of the spot vapors. To test 

 this, the spectrum of iron vapor in an electric arc 

 was photographed at different temperatures. 

 Some of the lines were found to strengthen, others 

 to weaken relatively, as the temperature was 



Fir,, ii. Iron (above) and Solar Spectrum (below). 



reduced. When compared with the iron lines in 

 sun-spots the changes were seen to he of the same 

 kind. The same test, applied to the vapors of 

 chromium, nickel, manganese, titanium, and other 

 metallic elements, previously identified in spots, 



FIG. 12. Effect of temperature on Spectrum of Vanadium: a In Carbon 

 Arc; b, c, and d in Electric Furnace at temperatures of 2600 

 j.VSf, smd 2150 C., respectively. 



