32 



Mr. G. J. Stoney on the Physical 



[Recess, 



composition of the sun's atmosphere. Probably nickel is the most abun- 

 dant of them. Of the others no lines appear in the sun's spectrum, except 

 those in reference to which they have a high specific opacity, in many 

 cases higher than that which iron has for any of its rays. There are, 

 therefore, but traces of them present ; and the appearance of the lines 

 agrees well with the situation in the sun's atmosphere assigned to them 

 by the masses of their molecules : chromium, projecting quite through the 

 iron atmosphere, produces a few lines of an intensity comparable with that 

 of the iron lines in their neighbourhood ; and the boundaries of cobalt, 

 nickel, copper, and zinc, appear to lie within that upper layer of iron 

 which sends forth iron lines. 



49. The appearance of the zinc lines is not incompatible with this 

 element's having the vapour- density usually supposed by chemists, viz., 

 32*5 instead of 65 ; but the evidence of the sun's spectrum, such as it 

 is, for it is scanty, owing to the paucity of the lines, seems to lean against 

 this hypothesis, unless a similar reduction is to be made in the case of all 

 the other metals of the atmosphere. But whatever uncertainty may rest on 

 this point, there is at least no doubt that barium cannot have a vapour- 

 density anything like so high as 137. At most it cannot exceed half that 

 number, which would barely raise the boundary of the barium atmosphere 

 within the lower part of the layer from which iron lines proceed ; and, if 

 it were not for objections on chemical grounds, the strength of such lines 

 as the barium lines 45*66, 49*37, and 61*43 would prompt us to suspect 

 for the vapour of barium even a lower density. But the strength of these 

 lines is probably due to the remarkably high specific opacity of the vapour 

 of barium in reference to them. There is plainly only a small amount of 

 barium in the sun's atmosphere. 



50. It will readily be perceived that it is vain to look for the cause of 

 any conspicuous line mapped by Kirchhoff, in any substance with a vapour- 

 density more than 70 times that of hydrogen. This narrows very much 

 the field in which to search for the origin of the darker of the lines enume- 

 rated in Table III., opposite, the table of unappropriated lines. Many 

 of these, as, for example, three of the five lines of the group at 60*3, are 

 probably due to manganese, and may be removed from this table, as soon as 

 a list of the thirty manganese lines, lately identified by Angstrom, shall 

 have been published. Others of them are probably some of the 460 iron 

 lines, produced by a continuous electrical current, or among the additional 

 lines which may be produced under like circumstances in others of the 

 elements which we have been heretofore examining. When all these are 

 eliminated it does not seem likely that many conspicuous lines between 

 G and B will remain to be traced to their source. Carbon is probably as 

 devoid of volatility as it is infusible ; or at all events the one probably bears 

 some proportion to the extraordinary eminence of the other. If this be 

 so, it cannot be a gas at the temperature of the situations from which dark 

 lines come, or at least not in sufficient quantity to produce visible effect. 



