xvi.] SOME RESULTS. 



In the case of each metallic element, then, we had first, a 

 comparison of its lines in the spectrum of the electric arc 

 photographed with the solar spectrum. After that we had 

 the long and short lines in the same substance photographed 

 on another plate. After that we had all the substances 

 which might exist as impurities in the first substance that 

 is to say, all the metallic elements photographed with their 

 lines their long and short lines, in precisely the same manner ; 

 and finally we had a comparison of the substance we wished 

 to study, say iron, with a spectrum of every other substance 

 which might exist in it as an impurity. It will be seen, 

 therefore, that an enormous number of photographs had to be 

 taken. The photographs, when obtained, were examined by a 

 powerful lens, and the various lines plotted down on a map. 



2. Some Results. 



I purpose now to deal, as briefly as may be, with some of 

 the results obtained. 



It will be clear at once, that as photography enabled us to 

 obtain a direct comparison of the lines visible in the spectrum 

 of each chemical element with the spectrum of the sun, we 

 were now in a position to see if there were any evidence of 

 the existence of substances in the solar atmosphere which had 

 hitherto remained undetected. 



Next, as I have already pointed out, we were enabled to 

 trace the lines in all spectra due to mutual impurities, and in 

 this way by careful elimination of such lines to produce maps 

 which should be above suspicion. 



The comparison photographs were limited necessarily to the 

 blue and violet portions of the spectrum, because the methods 

 since worked out by Captain Abney for photographing the other 

 regions were not then available, and of set purpose I limited it 



