334 M. E. Goldstein on Spectra of Gases. 



order, or band- and line-spectra, are closely related to the modes 

 of discharge. He believes he has established by a series of ex- 

 periments " that the line-spectrum of a gas only appears in the 

 disruptive discharge, the band-spectrum only in the continuous 

 discharge through the gas." After these facts have been estab- 

 lished, Wiillner tries to explain the spectra of different orders by 

 means of the different thicknesses of the luminous layer in the 

 two modes of discharge. In the disruptive discharge (accord- 

 ing to Wiillner) only a few molecules of the gas emit light ; in 

 the continuous discharge, on the other hand, nearly the whole 

 mass of the gas contained in the spectral tube is luminous. If 

 we accept the principles deduced by Zollner, the gas-spectrum 

 can only consist of a few luminous lines in the first case, while 

 the thick layer of the continuous discharge will show light of 

 all wave-lengths which the gas can emit at the temperature 

 in question. I shall now give the results of observations and 

 experiments which were made in reference to the above as- 

 sertions. 



The close relation between the two modes of discharge and 

 the two kinds of spectra which seemed to be established by 

 Wullner's experiments, became first doubtful to me in work- 

 ing with a tube filled with air under low pressure and with 

 a Leyden jar inserted between one of its electrodes and the 

 induction-coil. The image of the discharge in a rotating mirror 

 showed, besides continuous fields, groups of images of the tube 

 not wider than the tube itself. 



The observations were at first made with a mirror rotating about 

 four times a second, but were repeated with a velocity about 

 twenty-five times as great. The spectroscope showed only the 

 Z>07id-spectrum of nitrogen. Geissler's tube filled with hydrogen, 

 on the other hand, the capillary portion of which showed the 

 characteristic red colour when the spark was passing, gave only 

 widened fields in the rotating mirror, the colour of which was 

 everywhere of the same crimson colour. The spectrum consisted 

 of the well-known lines of hydrogen. A number of other tubes 

 filled with hydrogen gave the same result. Both experiments 

 contradict directly the law given by Wiillner. In order to arrive 

 at a definite conclusion, a close investigation seemed to be ne- 

 cessary. 



During the course of my experiments I found it often neces- 

 sary to introduce into the circuit a layer of air, which was some- 

 times replaced by a second tube filled with air under high pres- 

 sures. In these cases the tube filled with air under low pres- 

 sure always shows the band-spectrum ; the spark in air, as well 

 as in the second spectral tube, shows the line-spectrum. 



If we take the views of Wiillner as proved, we must assume 



