2 M. A. J. Angstrom on the Fraunhofer-lines 



which the spark passes ; also that, on account of the different 

 appearance of the lines in the metallic spectrum, it is possible 

 to distinguish it from that arising from the gas. This circum- 

 stance enabled me to construct figures of the spectra belonging 

 to the metals most commonly met with, and to determine the 

 relative position of the most prominent light-lines, with respect 

 not only to the lines of the aerial spectrum, but also to the 

 Fraunhofer-lines, with such accuracy as the means I could then 

 command permitted. I also showed that metallic compounds 

 and metallic sulphides have precisely the same lines in their light- 

 spectra as each of the different bodies of which the compound 

 consists, and that this circumstance offered a ready means of 

 determining the constituent parts of an unknown substance. 

 This circumstance by no means escaped my notice ; but for the 

 metals with which I was then engaged the method appeared not 

 sufficiently sensitive, and therefore inapplicable, although it has 

 since, according to the experiments of Bunsen and Kirchhoff, 

 shown a remarkable degree of sensitiveness in the case of the 

 alkaline metals. 



The results at which I arrived in that paper have since been 

 for the most part confirmed by Willigen* in his excellent paper; 

 he, however, employed, as the source of his electricity, a Ruhm- 

 korfFs inductive apparatus, and made important changes in the 

 method of observation by introducing between the two electrodes 

 of the instrument chemical solutions, especially combinations of 

 chlorine with the substances he wished to examine — a method 

 which, in imitation of him, I have adopted in my later researches. 



The Physical Cabinet at Upsala, having been last year pro- 

 vided with an optical theodolite by Pistor of Berlin, with an 

 induction-apparatus by Ruhmkorff, with prisms and glass 

 micrometer-scales by Steinheil, Bertand, and Mertz, I have 

 resumed these researches with the advantage of Dr. Thalen's 

 zealous assistance. 



The object of these researches is twofold : — 1st, a new exa- 

 mination of the solar spectrum, a determination of the lengths 

 of the waves, not only for the seven principal lines already de- 

 termined by Fraunhofer, but also for a sufficient number of in- 

 termediate lines, and the construction of accurate drawings of 

 the spectrum, without which measurements can have no prac- 

 tical utility ; 2nd, the determination of the length of the waves 

 for the various sorts of light which enter into the gas-spectra of 

 different metals, a determination which is best effected by 

 actually introducing these latter into the solar spectrum. 



§ 2. The following notice of the Fraunhofer-lines, and of the 

 conclusions to which they lead with respect to the composition 

 * Poggendorff's Annalen, vol. cvi. p. 610. 



