JBrusli Discharge in Water and Salt Solutions. 473 



with a lens it will be found that it has slightly decayed 

 (see fig. 4 in text). There is thus interposed between the 

 point and the outer liquid a very short capillary. The 

 resistance of this capillary evidently enabled the potential 

 to rise and thus give a brighter discharge. 



If a fine wire is used (about *1 mm. diameter), then after 

 continued use it will be found that the lithium lines have 

 decreased very considerably in brightness, the rest of the 

 spectrum being unchanged. The point, in one case, when 

 examined was found to have decayed so much that a capillary 

 of 2 mm. in length intervened between it and the liquid. 

 It was this that first suggested to me the examination of the 

 capillary discharge with the apparatus shown in fig. 2. 

 Fused silica was used as the material because glass capillaries 

 cracked too readily with the heat. It was found with capil- 

 laries raneinff from '05 mm. diameter to 1 mm. diameter in 

 various strengths of solutions, that the lithium lines appeared 

 only very faintly. If the wire electrode which was immersed 

 in the fused silica tube were now brought just to touch the 

 top of the capillary, it became covered with a faint luminous 

 glow which gave the spectrum of hydrogen and lithium (if 

 a solution of a lithium salt were used). The lithium spec- 

 trum grew brighter as the point was pushed further down 

 into the capillary, while the discharge at the bottom of the 

 capillary changed over to the brush discharge (the bubble 

 discharge as described above). Just before the point reached 

 the bottom of the capillary the brush became fainter, and 

 the luminosity vanished completely as the wire emerged 

 through the capillary. 



To produce the spectra in fig. 7, A & B (PI. V.) the image 

 of a capillary was focussed on the widened slit of a spectro- 

 graph. The capillary tapered, being narrowest at the 

 bottom. The discharge occurred only in this narrow portion 

 of the capillary when the electrode was kept away from it. 

 Fig. 7, B is the spectrum under these conditions. The capil- 

 lary is inverted in the photograph so that the spectrum of 

 the narrow portion appears at the top (a) instead of the 

 bottom (b). It will be seen that the lithium lines are very 

 feeble. Fig. 7, A is the spectrum of the same capillary, the 

 wire electrode now being just at the top of the capillary 

 (bottom in the photograph). The spectrum of the glow 

 surrounding it is shown clearly in fig. 7, A, b. Thus while 

 the hydrogen gives a bright spectrum both in the narrow 

 part of the capillary and round the point, the lithium lines 

 (and the D lines of sodium) appear brightly in the light 

 surrounding the point, but scarcely at all in the narrow part 



