470 Mr. H. Smith : Spectroscopic Study of the Electric 



shows the series lines brightly and secondary lines faintly 

 (see fig. 9, a). A slightly broader capillary shows the 

 secondary lines with much greater relative intensity (see 

 fig. 9, b). Thus increasing the current density in the capil- 

 lary has the same effect as increasing the intensity of the 

 discharge through the brush, except that in the former case 

 little broadening of the series lines occurs, and the relative 

 intensity of the series lines is not altered. 



These results are quite compatible with those obtained 

 with a discharge-tube. Both spectra appear with the ordinary 

 induction-coil discharge, while the secondary is reduced or 

 disappears when the tube forms part of a condenser and 

 spark-gap circuit*. 



Oxygen. 



The series spectrum of oxygen is much feebler than that 

 'of hydrogen. Its behaviour, however, is very similar, 

 though the lines show no appreciable broadening nor any 

 variation of intensity among themselves. They appear in 

 the brush in distilled water only very faintly. In the un- 

 condensed brush in solutions they do not appear at all. but 

 they show distinctly in the spectrum of the condensed brush 

 when the discharge is heavy. They are shown fairly well 

 in PI. V. fig. 2,e. The line \= 6157 is easiest to detect. It can 

 be seen a little to the right of the lithium orange line \ = 6104 : 

 fig. 3, d, PL V., shows these two lines of nearly the same 

 intensity. The fine capillary discharge shows the series 

 spectrum best (see PL V. fig. 8, a or fig. 9, a). The wider 

 the capillary, the fainter are the series lines (compare 

 fig. 9, a & b : b is with the slightly wider capillary). Indeed 

 with a capillary about "2 mm. wide the series spectrum is 

 difficult to detect. Within the limits of these experiments, 

 then, it would appear that the higher the current density, 

 the brighter will the series spectrum be. 



The many-lined or elementary-line spectrum of oxygen 

 behaves in a somewhat inexplicable way. Its behaviour is 

 quite different from that of the secondary spectrum of 

 hydrogen. It appears in the brush in distilled water faintly, 

 but stronger than the series lines (see PL V. .fig. 6, a & b). 

 The doublet at \ = 4416 is the most readily distinguishable 

 part of the spectrum. It appears also in the brush in solutions, 

 occurring only at the feebler, and vanishing almost completely 

 at the higher discharges (compare PL V. fig. 4, a, b, c, d). 

 It is also brighter in a solution of! lithium sulphate than in a 

 solution of lithium carbonate (compare fig. 3 with fig. 4, PLV.) . 



* Dufour, Ann. Chim. ct Phys. ix. pp. 403-5 (1906). 



