18 PROCEEDINGS OP THE AMERICAN ACADEMY 



occur in the case of iron and other spectra, and which alone can serve 

 as evidence in such cases, are conspicuously absent. 



Among the metals whose existence in the solar atmosphere has 

 seemed probable, we have examined the following : — 



Bismuth. — The line of the above metal at 4722.9, the only line of 

 bismuth in the arc in that whole region, coincides perfectly with the 

 more refrangible of a very faint pair of solar lines. 



Tin. — The solitary tin line at 4525, thought by Lockyer to coin- 

 cide, falls directly between two fine lines in the solar spectrum. 



Silver. — Lockyer mentions a certain possibility of silver in the 

 solar atmosphere from the apparent agreement of two of its nebulous 

 lines with solar lines. One of these we have never been able to find 

 in the course of many photographs of the region in which it is given 

 by him. 



We find seven lines of silver between 4000 and 4900. Of these 

 seven, three are what Thalen calls nebulous ; so broad and hazy tbat 

 their true positions cannot be determined with much accuracy. These 

 lie at about 4055.5, 4063.6, and 4212. A fourth line at 4023 is of 

 the same general character, but has a sharp reversal which agrees 

 with a solar line. The remaining three lines are represented in the 

 sun, and are given by Thalen in the spark spectrum of the metal. 



4476.2. Very strong line ; nebulous on lower edge. Sun line 

 strong. (Thalen, 4475.) 



4668.8. Strong, solitary line. (Thalen, 4666.5.) 



4874.3. Fairly strong. (Thalen, 4874.) 



Thus, between the limits given above, every line of silver, as far as 

 can be determined, coincides with a solar line. 



Potassium. — We could find but two lines of potassium, the same 

 that were examined by Lockyer, 4044.5 and 4048.35. Each line is 

 reversed four times, which increases the difficulty of locating them 

 exactly. 4048.35 seems to agree with a solar line. The solar line 

 near 4044.5 is very faint, and it is next to impossible to decide the 

 question of an agreement. 



Lithium. — The blue line of lithium presents a curious case. The 

 very broad and nebulous line has a rather sharp reversal near the 

 centre, and somewhat toward the lower edge a broader and less clearly- 

 defined reversal. Both these reversals agree with solar lines at 

 4602.5 and 4603.2. It is possible that one of the reversals may be 

 due to the presence of some other substance, say calcium ; but if that 

 were true, it would seem that both reversals would be nearly, if not 

 quite, obliterated. Further experiment may clear the matter up. 

 4603.2 is given to iron by Thalen. 



