298 Profs. C. Eunge and F. Paschen on 



The doubts we expressed in our former communication in 

 connexion with the series beginning with 7065 have been 

 confirmed. The two lines there indicated as of questionable 

 origin belong to hydrogen, and the lines 7065 and 5048 be- 

 long to two distinct series, which with four others now em- 

 brace all the lines of the spectrum. 



The following list (see Appendix) contains the newly 

 discovered lines, and those of which the connexions with 

 them have now been ascertained. 



The other series of lines can also be traced farther in the 

 new tubes. 



We have, accordingly, here to do with six series, among 

 which it twice happens that two series converge towards the 

 same place. Two of these converging series, namely, those 

 beginning at 7065 and at 5876, consist of double lines with 

 equal differences of oscillation-frequencies *. We associate 

 these with the remaining one which has double lines, that 

 which begins at 1'12/a in the infra-red. Two at all events of 

 the three other series have no double lines ; they diverge 

 from the same situation, and we unite them with the remain- 

 ing series into a second system f. 



Both the systems prove to have a similar appearance, and 

 all the lines of the first system are stronger than the corre- 

 sponding lines of the second system. 



Further, it appears that both these spectra are very similar 

 to the spectra of the alkalies. In the spectrum of each of the 

 alkalies we find two " Subordinate Series " (of lines that 

 are double, with the exception of the lithium spectrum in 

 which no pairs have been observed) accompanied by a much 

 stronger " Principal Series." The Subordinate Series diverge 

 from the same situation, and the lines of the brighter of them 

 are more closely spaced. On the other hand, the Principal 

 Series extends farther in the more refrangible direction. All 



* Note by the Translator. — The presence of double lines in a series 

 seems to indicate that the single motion in the gas which originates the 

 whole series consists of partials, each of whicji is in general elliptic ; 

 "becoming linear when the constituents of the double lines are of equal 

 intensity, and circular when, as in lithium, one of them vanishes. That 

 the double lines have equal intervals on a map of oscillation-frequencies 

 seems to betoken that the path of that motion in the molecules of the 

 gas to which the series is due is affected by an apsidal shift. See 

 ' Scientific Transactions of the Royal Dublin Society,' vol. iv. (1891) 

 p. 571. 



t Note by the Translator. — In the diagram the second system is upper- 

 most, next to the hydrogen spectrum ; and the first system, which con- 

 tains the helium line, is under it, next to the lithium spectrum. 



