344 THE CHEMISTRY OF THE SUN. [CHAP. 



look for it in iron with the intensity coil. I at once found it, 

 and it is sympathetic with the line at 4923 in the spark as it 

 is in the flames themselves. Though omitted by Thalen (most 

 likely accidentally, though it may well be that he did not use 

 sufficient tension to bring it out strongly), I have since found 

 that it is recorded as an iron line by other observers. 



Work in a laboratory at Kensington suggested that the 

 observations in the Observatory of the Collegio Romano at Rome 

 indicated that an omission had been made in a table of lines 

 constructed at Upsala ! 



FIG. 114. Tacchiui's observations of new prominence lines when the iron lines 



disappeared. 



There is one very beautiful case that comes out from Tacchini's 

 observations. From the beginning of February, 1872, Tacchini 

 had observed the two iron lines 4923 and 501 7*5, when suddenly 

 the whole rhythm of his observation was broken, and at the 

 end of December, 1872, these iron lines ceased to be visible in 

 the flames altogether. 



On no one occasion after this for some time was either of 

 these iron lines observable, but from January to September, 



