512 Mr. J. N. Lockyer on Spectrum- Analysis. [Nov. 27 } 



3. In cases of coincidences of lines found between various spectra the 

 line may be fairly assumed to belong to that one in which it is longest 

 and brightest. 



A description of some photographs of spectra is then given, a photo- 

 graph of the coincident lines of calcium and strontium being amongst 

 them, and proving that strontium occurs in the sun ; and the section 

 concludes with a brief description of the method employed in making the 

 new map, showing lengths and thicknesses, and enumerating coincident 

 lines. This is done thus : papers are pasted on to photographs of the 

 solar spectrum on glass ; the lengths of the lines of the metallic spec- 

 trum under examination (e. g. that of iron) are marked on this paper in 

 prolongation of the solar lines to which they correspond. They are then 

 copied upon a map; and another piece of paper being fixed down, another 

 spectrum is proceeded with in the same way. 



IV. The preliminary inquiry into the existence of elements in the Sun not 

 previously traced. 



The previous researches having shown that the former test for the 

 presence or absence of a metal in the sun, namely the presence or ab- 

 sence of its brightest or strongest lines in the average solar spectrum, was 

 not conclusive, a preliminary search for other metals was determined on ; 

 and as a guide, Mr. R. J. Friswell was requested to prepare two lists, 

 showing broadly the chief chemical characteristics of the elements traced 

 and not traced in the sun. 



The Tables showed that, in the main, those metals which had been traced 

 formed stable compounds with ox}^gen. 



The author therefore determined to search for the metals which formed 

 strong oxides, but which had not yet been traced. 



The result up to the present time has been that strontium, cadmium,, 

 lead, cerium, and uranium would seem with considerable probability to 

 exist in the solar reversing layer. Should the presence of cerium and 

 uranium be subsequently confirmed, the whole of the iron group of metals 

 will thus have been found in the sun. 



Certain metals forming unstable oxides, such as gold, silver, mercury, 

 &c. were sought for and not found. The same was the case when chlorine, 

 bromine, iodine, &c. were sought by means of their lines produced in tubes 

 by the jar-spark. These elements are distinguishable as a group by 

 forming compounds with hydrogen. 



It is observed that certain elementary and compound gases effect 

 their principal absorption on the most refrangible part of the spectrum 

 when they are rare, and that as they become dense the absorption 

 approaches the less-refrangible end — that the spectra of compounds are 

 banded or columnar, the bands or columns lying at the red end of the 

 spectrum — that the absorption spectra of chlorine, iodine, bromine, &c. 

 are columnar, and that these are broken up by the spark just as the band 



