172 Mr. J. N. Lockyer. Researches in Spectrum [Dec. 12 r 



the spectrum which we meet with in the spectra of almost all bodies, 

 some of which have already been pointed out by Mas cart, Cornu, and 

 myself. Now the facts indicate that these two triplets are not due 

 to the vibration of the same molecular grouping which gives rise to 

 most of the other lines. They are as follows. In many photographs 

 in which iron has been compared with other bodies, and in others 

 again in which iron has been photographed as existing in different 

 degrees of impurity in other bodies, these triplets have been seen 

 almost alone, and the relative intensity of them, as compared with the 

 few remaining lines, is greatly changed. In this these photographs 

 resemble one I took three years ago, in which a large coil and jar were 

 employed instead of the arc, which necessitated an exposure of an hour 

 instead of two minutes. In this the triplet near G is very marked ; the 

 two adjacent lines more refrangible near it, which are seen nearly as 

 strong as the triplet itself in some of the arc photographs I possess, 

 are only very faintly visible, while dimmer still are seen the lines of 

 the triplet between H and li. 



There is another series of facts in another line of work. In solar 

 storms, as is well known, the iron lines sometimes make their appear- 

 ance in the chromosphere. Now, if we were dealing here with one 

 molecular grouping, we should expect the lines to make their appear- 

 ance in the order of their lengths, and we should expect the shortest 

 lines to occur less frequently than the longest ones. Now, precisely 

 the opposite is the fact. One of the most valuable contributions to 

 solar physics that we possess is the memoir in which Professor C. A. 

 Young records his observation of the chromospheric lines, made on 

 behalf of the United States Government, at Sherman, in the Rocky 

 Mountains. The glorious climate and pure air of this region, to which 

 I can personally testify, enabled him to record phenomena which it is 

 hopeless to expect to see under less favourable conditions. Among 

 these were injections of iron vapour into the chromosphere, the record 

 taking the form of the number of times any one line was seen during 

 the whole period of observation. 



Now, two very faint and short lines close to the triplet near Gr were 

 observed to be injected thirty times, while one of the lines of the 

 triplet was only injected twice. 



The question next arises, are the triplets produced by one molecular 

 grouping or by two ? This question I also think the facts help us to 

 answer. I will first state, by way of reminder, that in the spark 

 photograph the more refrangible triplet is barely visible, while the one 

 near G is very strong. Now, if one molecular grouping alone were in 

 question, this relative intensity would always be preserved, however 

 much the absolute intensity of the compound system might vary, but if 

 it is a question of two molecules, we might expect that, in some of the 

 regions open to our observation, we should get evidence of cases in 



