ApiiiL 1, 1896.] 



KNOWLEDGE. 



89 



the same limit. The same is the case -with sodium and 

 potassium ; but wliilst the lines of lithium are single those 

 of sodium and potassium are double, and the successive 

 doublet intervals are al-s\-ays the same. We might there- 

 fore express the case a little dift'erently by saying that 

 sodium and potassium each give two pairs of subordinate 

 series, and that the one series of each pair is displaced 

 throughout as compared with its companion series by a 

 constant oscUlation-frequency.* And, further, this con- 

 stant difl'erence is the same as that sho-wn by the two 

 components of the first doublet of the principal series. 



The accompanying diagrams will exhibit the character 

 of these relations for the spectra of lithium and sodium 

 better than much verbal explanation. In the first diagram 

 the upper line for lithium and sodium shows the complete 

 spectrum of the element ; its analysis into principal and 

 first and second subordinate series is shown below. The 

 second diagram corresponds to that given by ^Ir. llanyard 

 for hydrogen in the paper referred to above, and is intended 

 to show the convergence curves of the different series. In 

 each case the scale adopted is one of oscillation-frequencies 

 to the metre. Doublets are shown throughout as single 

 lines, the scale of the diagrams not permitting them to be 

 shown as distinct pairs. ] 



* Prof. Hartley had sliown that this relation held good fo>: the 

 triplets of niaguesiimi, oadmiuia, and zinc as early as 18S2 {Joiirn. 

 Chemical Sociely, 1882 and 1883). 



t The constants given for these spectra by Profs. Kayser and Runge 

 are as fallows (Ahh. der Kgl. Freuss. Aktnl. dcr Whsen., Berlin, 

 1890) :— 



Lithium — 



Principal Series 

 Subordinate ,, I. 

 „ II. 

 Sodium — 



Principal Series 

 Subordinate ,, 



A „ B , C . 



4-35193 X 10 1-12186 x 10 9-069 x 10 



2-858674 1-096255 1-847 



2-866669 122391 231700 



I. a. 



I. b. 



II. a. 

 II. b. 



4149634 

 2-454912 

 2-456583 

 2-447534 

 2 449484 



1-27040 

 1-20726 

 1-20715 

 1-10065 

 1-10153 



843-841 



197-891 



197-935 



4- 148 



3-487 



The lines in the two spectra are as follows : — 

 Lithium. 

 Wave-lengths expressed in tenth-metres. 



Profs. Kayser and Eunge have more recently analysed 

 the spectra of a large number of elements after the same 

 manner in which they had treated those of lithium and 

 sodium, but their results for these need not detain us now. 

 But when Runge and Paschen followed up their careful 

 elaboration of the spectrum of the cleveite gas by a similar 

 analysis, a very striking circumstance was revealed. The 

 cleveite lines gave, not one series like hydrogen, nor three 

 like lithium, but six, and of these some were series of 

 single lines, some of doublets. 



" We have," the observers report," " 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 5870, 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 fj. 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 remaining 

 series into a second system. 



" Both the systems prove to have a similar appearance, 

 and all the lines of the first system are stronger than the 

 corresponding lines of the second system. 



" Further, it appears that both these spectra are very 



similar to the spectra of the alkalies We can 



distinguish in each of them two subordinate series 

 diverging from the same situation, of which the brighter 

 is the more closely spaced. Moreover, each system 

 contains a principal series whose lines are stronger than 



Prof. Snow has observed tlie line corresponding to n = 3 of the 



second subordinate series. 



In the following tables of the sodium lines only the first component 

 of each doublet is given ; but the difference between the two com- 

 })onents is added, as tliis will render more clear the distinction between 

 the doublets of the principal and of the subordinate series. 



SoDim. 

 Wave-lengths expressed in tenth-metres. 



Principal Series. 



5896-16 ;— 5-97 

 330307 ;— 60 



2852-91 



2680-46 



2593-98 



2543-85 



251223 



First Subordinate 

 Series. 



6161-15;— 6-53 

 5153-72;— 4-53 

 4752-19 ;-3-83 

 4^546-03 ;— 3-28 

 4423-7 ;— 3-5 

 4343-7 



Second Subordinate 

 Series. 



8200-3 ;— 12-0 

 5688-20;— 5-36 

 4983-53;— 423 

 4669 4 ;— 4-2 

 4500 ;— 5-7 

 4393 7 ;— 3-0 

 4;i90-7 



Oscillation-frequencies to the m&tre. 



1696019; -I- 1719 

 3027487 ; + 550 



3505193 



3730703 



3855080 



3931049 



3980527 



1623074 J ■(• 1722 

 1940346 ;■^ 1707 

 21114293 ;-^ li;97 

 2199721 ; + 1589 

 2260551 ; -I- 1790 

 2302185 



1219468;-H787 

 17.58CX>7;-^lt>58 

 2006610; + 1701 

 2141603 ;■^ 1928 

 2222222 ; -f 2819 

 2275986 ;-H 1555 

 2311765 



M. Hccqiiorcl has observed the lino corresponding to « =: 3 of the 

 first subordinate series. A pair of lines, not indutled in the above 

 table, is also feen at A = 5075 92 ; — 552 ; oscillalion-frei|uency, 

 1761829 ; + 1715. Dr. .foluistone Stonev, in an important paper on 

 the " Analysis of tlie Sjiectruin of Sodium," rcail before the Royal 

 Dublin Society, 1891, November 18th, claims this jHiir as corre- 

 sponding to a negative value of ^. 



• I'roc. BerUn Aiad., June 20th, 1895. Vhil. Mag.. Sept., 1895, 

 p. 293. 



