of Light Radiations emitted by Iron Vapour. 



15 



evidence for the existence of series, such as are known in 

 the case of: a number of other elements, has so far been 

 detected, it is impossible to pass over without comment the 

 curious groups of lines which have been encountered in 

 various parts of the spectrum. These groups consist of 

 three, four, or more lines, the characters and relative posi- 

 tions of which are such as to suggest some orderly arrange- 

 ment. 



In order to facilitate the search for these groups, a series 

 of normal spectra were drawn, each spectrum containing 

 lines of only one class. To the three classes given by the 

 flames was added that for the self-induction spark from 

 which al] the flame lines had been eliminated. 



The principal groups obtained in this way are given here- 

 after. A 1? A 2 , &c, signify first, second, &c, differences. 

 The symbol d ? means that the line is a double one in the 

 arc, but that it was not resolved by my spectrograph. It 

 was, therefore, not possible to ascertain which of the two 

 components belongs to the group, and an error may have 

 been made in the selection of the line. An asterisk added 

 to the wave-length number indicates, as before, that the line 

 is marked to the nearest Angstrom unit on the accompanying 

 plates. 



Wave-lengths. 



r*3679-92 

 J *3705-56 



a 'i 3722-57 

 I 3733-32 



f*4375'93 



I *4427"31 



T-i *4461-65d? 



1*4482-27 



f*3856-38 

 n \ 3878-73 rf? 

 P-1 3895-65 



L 3906-47 



f*3719-93 

 \ *3737-13 

 [*3745-55tf? 



f *3859-90 



\ *3886 29 



*389970 



Class I. Groups. 



Oscillation . 



Frequency. 1- 



27174 5 

 26986-5 

 26863-2 



26785-8 



22852-3 



22587-1 

 22413-2 

 223101 



19951-8 

 19351-7 

 18977-0 



18768-6 



25931-0 

 25781-6 

 25669-7 

 25598-6 



26882-2 

 26758-5 

 26698-4 



25900-7 

 25731*5 

 25643-0 



188-0 

 123-3 



77-4 



265-2 

 173-9 

 103-1 



600-1 

 374-7 

 208-4 



149-4 



111-9 



71-1 



1237 



601 



169-2 



88-5 



64-7 

 45-9 



91-3 



70-8 



225-4 

 166-3 



37-5 



40-8 



18-8J 



20-5 



59-1 



