H. and K. lines of the Solar Spectrum. 245 



that the walls of the glass vessels are heated to incandescence ; 

 moreover E. Wiedmann* has shown that the heat of electrical 

 discharges in Geissler tubes has been much exaggerated. A 

 photograph was taken of the light from a Geissler tube by 

 means of a rapidly revolving mirror. Besides the tube and in 

 the same circuit was a spark gap between magnesium terminals. 

 The duration of the light of the Geissler tube was one fourth 

 of that of the spark between the magnesium terminals in air. 

 There was absolutely no duration of the light of the Geissler 

 tube due to a supposable incandescence of the glass. The light 

 in the Geissler tube arising from powerful disruptive discharges 

 is the strongest and most instantaneous light which has been 

 obtained and would be useful in the study of rapid motions. 



If the glass is not vaporized by the discharges I have 

 employed, the spectrum of calcium cannot be produced in the 

 capillary of the glass vessels. A direct test of the question 

 whether the reversed lines observed by me are due to the glass 

 is afforded by the use of quartz vessels of which the ends were 

 closed by metal plates, there being a complete absence of 

 glass and previous investigation having shown that the metallic 

 plates or terminals gave no metallic spectra. In the case of 

 quartz the powerful disruptive sparks produced absolutely no 

 corrosion of the walls of the quartz capillaries ; and the 

 reversed line at approximately wave length 4227 and wave 

 lengths 3968, 3963, H.H. of the solar spectrum came out with 

 the same intensity as in the case when glass was employed. 

 Moreover the strong calcium lines toward the ultra-violet 

 besides those which apparently coincide with the H.H. lines 

 of the solar spectrum were conspicuously absent. 



The reversed lines therefore which I described in my previ- 

 ous article and which are shown on the plates of that article 

 are not due to calcium. These lines may arise from an 

 electrical decomposition of residual air. It seems impossi- 

 ble to fill spectrum tubes with perfectly dry and pure hydro- 

 gen ; traces of air must enter from the purifying and drying 

 apparatus ; and the impurities may be brought to light 

 by powerful discharges. I have shown in a previous paper 

 that the electrical decompositions in a tube apparently filled 

 with pure hydrogen can produce various spectra, among them 

 that of argon. * The most promising method of obtaining pure 

 dry hydrogen appears to be by the use of liquid hydrogen. 



In this Journal for December, 1902, I spoke of a remark- 

 able reversal of lines in the ultra-violet which were obtained 

 by the use of quartz tubes. 



Fig. 4 shows these lines with a companion spectrum of magne- 

 sium. These reversed lines apparently coincide with spark lines 



*Wied. Ann., vi, 1878. 



