XVL] NEW SOLAE ELEMENTS. 219 



The photographic evidence which was utilized in this portion 

 of the inquiry consisted of the longest lines visible in the 

 respective spectra. For the reasons stated on page 156 the 

 fact of these lines being reversed in the solar spectrum must be 

 considered as strong evidence in favour of the existence in the 

 sun of the metals to which they belong. Where, however, there 

 is only one line, as with lithium, rubidium, and some other 

 substances, the evidence cannot be considered final, and until 

 a larger number of coincidences is determined, the presence of 

 these metals in the sun's atmosphere can only be said to be 

 probable. 



It had, moreover, to be borne in mind that, in addition to the 

 long lines which a spectrum may contain in the red, yellow, or 

 orange, long lines may exist in the ultra-violet region, so that 

 the absence of such metals from the sun cannot be absolutely 

 affirmed until a complete survey of this region has been 

 completed. 



The first thing to be done was to see if the photographs 

 confirmed the results already announced in 1873, with regard to 

 strontium, lead, cadmium, cerium, and uranium. They did, as 

 the following table will show : 



Strontium. Reversal of 4 lines at wave-length 4029 '6, 4076*77, 

 4215-00, and 4607*5. 



Lead. Reversal of 3 lines at w.l. 4019*28, 4056*8, and 4061-25. 



Cadmium. Reversal of 2 lines at w.l. 4677 '0 and 4799 '00. 



Cerium. Reversal of 2 lines at w.l. 3928*7 and 4012*0. 



Cranium. Reversal of 3 lines at w.l. 3931*0, 3943*0, and 

 3965-8. 



The photographic evidence seemed also conclusive in the 

 case of the following substances: 



Potassium. Reversal of 2 lines at wave-length 4042*75, and 

 4046-28 (apparently the only potassium lines in this region of 

 the spectrum). 



