340 M. E. Goldstein on Spectra of Gases. 



A tube which has different widths in different parts shows 

 sometimes, when the discharge is disruptive, the line-spec- 

 trum at the poles (which are generally introduced into the 

 wider part of the tube) ; the remaining part of the wider end 

 gives the band-spectrum ; and the narrow part shows again the 

 line-spectrum. The rotating mirror shows, as was to be ex- 

 pected, that the discharge is the same in all parts of the tube. 



The discharge of a Leyden jar in air under rather high pres- 

 sure shows sometimes a strange phenomenon. Near to the 

 negative end of the tube appears a place which is of yellowish 

 pink colour. The spectrum-analysis of this point gives the 

 bands of nitrogen ; the remaining part of the tube shows only 

 the lines of nitrogen. The rotating mirror gives the image of 

 the tube together with its pink point as one whole. (Velocity 

 of rotation about 40 per second.) 



The spectrum of the pink point makes rather the impression 

 of a continuous spectrum. g The bands are wide and indistinct; 

 if the phenomenon is at its best, only the blue and violet bands 

 can be distinguished from the illuminated ground. I shall try 

 further on to give an explanation of this phenomenon. 



I believe it to be established by the above experiments, that 

 the different spectra have nothing to do with the mode of 

 discharge. 



I could not confirm by experiment the second proposition of 

 Wiillner — u In the disruptive discharge only a few molecules, 

 therefore a very thin stratum of the gas, is luminous." I could 

 obtain sparks in rarefied gas as much as several centimetres 

 in diameter. The colour of such sparks in air is blue or pink, 

 with the various tints which can be produced by changes in 

 intensity and saturation of these colours. 



The colours of thick sparks in hydrogen are bluish white, flesh- 

 coloured, yellowish, yellowish red, and crimson. 



Not only are those sparks thick which give the band-spectrum, 

 but also those (and it is of these Wiillner was thinking) which 

 give a line-spectrum. 



By introducing sparks and jars in the outer circuit, we may 

 succeed in obtaining sparks blue in air and red in hydrogen 

 which give line-spectra, and which filled entirely tubes of 1^ 

 centim. diameter. I shall mention subsequently observations 

 on the negative light which refer to this point. 



Another assertion of Wullner's says that the band-spectrum 

 is always produced by a thick discharge. Part of the above can 

 already be produced as evidence to the contrary. In capillary 

 tubes band-spectra are seen, while line-spectra may be given out 

 by much thicker layers of air. 



The induction-spark in air under ordinary pressure, which is 



