388: Royal Society :— 



appear in the spectra of the other metals are shorter than the 

 longest lines of those metals. Hence we are justified in assuming 

 that short lines of iron, cobalt, nickel, chromium, and manganese, 

 coincident with long and strong lines of calcium, are really due to 

 traces of the latter metal occurring in the former as an impurity. 

 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 

 photograph 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 spectrum under 

 examination (e. g. that of iron) are marked on this paper in pro- 

 longation 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. 



IY. 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, narnely the pre- 

 sence or absence 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. II. J. Iriswell 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 oxygen. 



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, cad- 

 mium, lead, cerium, and uranium would seem with considerable 

 probability to exist in the solar reversing layer. Should the pre- 

 sence 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 distin- 

 guishable 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 



