FOURTH PAPER. maps also bears out this view with regard to the outer layers; for in the case of H and Na all the lines are reversed; in the case of Mg, about which there was a doubt in Ångström's observations, only one line is possibly dropped, and this is not certain. When we come, however, to the elements with higher atomic weights, the number of Difference lines reversed is less. But the maps also show that when between once the higher layers of the chromosphere, where less higher and lower strata constant action goes on, are passed, atomic weight ceases of chromoto be a guide; and we are therefore driven to other considerations, which promise to largely increase our knowledge of the kind of action at work in the solar atmosphere and the cyclical variation of that action. sphere. The maps which accompany this communication have been made by my assistant, Mr. R. J. Friswell. They have only been revised by myself. I am anxious to take this opportunity of testifying to the zeal and ability he has displayed in a research necessarily very tedious from its character, and requiring great patience and care. [It has been found impossible to give here all the maps and tables which appear with this communication in the Phil. Trans. The accompanying Plate, however, in which some of the maps are reduced, will give an idea of the results of this research.] FIFTH PAPER. Researches in Spectrum Analysis in connection with the [ABSTRACT.2] THE observations in this paper are a continuation of those referred to in the previous communication bearing the same title. They deal (1) with the spectrum of chemical compounds, and (2) with the spectra of mechanical mixtures. I. Chemical Compounds. Several series of salts were observed; these series may be divided into two :-Ist, those in which the atomic weights varied in each series; 2nd, those in which the associated elements varied in each series. The following salts were mapped : FIFTH PAPER. spectra Pb F2, Pb Cl2, Pb Br2, Pb I; Sr F, Sr Cl, Sr Br2,Sr I2; Salts whose Ba F2, Ba Cl2, Ba Br2, Ba I; Mg F2, Mg Cl2, Mg Br2, Mg I; Na F, Na Cl, Na Br, Na I. 2 The conditions of the experiments are described; the same aluminium cups, described in the first paper, were used, and the poles were arranged in such a manner that they could at will be surrounded with any gas or vapour. Hydrogen was used in some of these experiments; it was purified in the usual manner by drying and freeing from traces of sulphuretted hydrogen; it was then passed over clean cut pieces of sodium, and admitted to the poles. An induction-spark from five one-pint Grove cells was used, the circuit being without the Leyden jar. Proc. R. S. vol. xxi. p. 285, No. 144. This paper will appear in extenso in the forthcoming volume of the Philosophical Transactions. were observed. FIFTH PAPER. The lines The lead compounds behaved (in air) as follows:The fluoride gave the eleven longest lines of the metal, but four were very faint. The chloride gave nine lines; one of these is very short. The bromide gave six lincs, but one is a mere dot on the pole. The iodide gave four lines distinctly, and two as dots, one of which is scarcely visible. It is pointed out that the decrease in length and number die out in of lines follows the increase in the atomic weight of the the order of their length. non-metallic element, the lines dying out in the order of their length. Barium was next experimented on, the same series of salts being used. A marked departure from the results obtained in the case of the lead compounds was observed, especially in the case of the fluoride, its spectrum being much the simplest; in fact, it consisted of only four lines. Strontium behaved like barium, and so did magnesium Anomalous fluoride. This anomalous behaviour was found to be most behaviour probably due to the exceedingly refractory nature of these of fluorides. fluorides, all of them being quite infusible, and non-volatile in any spark that was used. Sodium salts. Flame spectra as compared with low Sodic fluoride, sodic chloride, sodic bromide, and sodic iodide exhibited a behaviour exactly the reverse of that of lead, i.e. the iodide showed most of the metallic spectrum. The difference between flame-spectra and those produced by a weak electric discharge are then discussed. Beads of the chlorides, &c., were heated in a Bunsen-gas tension elec flame; Ba I, gave a "structure" spectrum (since proved to tric spectra. be due to the oxide) and the line at wave-length 55345. by very far the longest metallic line of barium. The bromide behaved like the iodide, and so did the chloride, except that its spectrum was more brilliant. Baric fluoride gave scarcely a trace of a spectrum, the oxide structure being scarcely visible, and 5534'5 very faint indeed. The strontium salts follow those of barium-4607'5, the longest strontium line appearing in conjunction with an oxide spectrum. The strontic fluoride, however, refused to give any spectrum whatever. These results are compared with those obtained with the weak spark, and it is shown that the difference is one of degree; e. g. baric bromide gives 25 lines in the spark; these are the longest lines. In the flame it gives but one line; but this is the longest of all the barium lines, and indeed very far exceeds all the others in length. When the flame-spectra are compared with those produced by the low tension spark, the spectra of the metals in the combination are in the former case invariably more simple than in the latter, so that only the very longest line or lines are left. FIFTH PAPER. oxides seen in all flames. Some experiments made by Mr. R. J. Friswell to deter- Spectra of mine the cause of the similarity of the spectra of the various salts of the same metal observed in air are then given, the conclusion being that the spectrum observed is really that of the oxide. Kirchhoff and Bunsen's, Mitscherlich's, and Clifton and Roscoe's prior conclusions on the points investigated are stated at length; and it is shown that the observations recorded, taken in conjunction with the determination of the long and short lines of metallic vapours, are in favour of the views advanced by Mitscherlich, Clifton and Roscoe. For while the spectra of the iodides, bromides, &c., of any element in air are the same as stated by Kirchhoff and Bunsen, the fact that this is not the spectrum of the metal is established by the other fact, that only the very longest lines of the metal are present, increased dissociation bringing in the other metallic lines in order of their length. Results ob tained by other observers. Spectra in an atmo sphere of The spectra have been mapped with the salts in hydrogen: here the spectra are different, as stated by Mitscherlich; and the metallic lines are represented according to the hydrogen. volatility of the compound, only the very longest lines being visible in the case of the least-volatile one. The following are the conclusions arrived at: 1. A compound body has as definite a spectrum as a |