346 Spectra of Hydrogen and the Spectrum of Aqueous Vapour. 



we see that the main hydrogen lines are narrowed and certain 

 hydrogen lines are so faint as to be hardly visible even on the 

 negative. 



Pig. 3. 





Fio-,4. 



Fig-. 6. 



Fio-. 7. 



The general character of the spectral lines of hydrogen in 

 respect to breadth and intensity, seems not to depend so much 

 upon mere pressure and apparent temperature (temperature 

 deduced from calculations of electrical energy in electrical 

 discharges), as upon electrical dissociations of gases : of 

 aqueous vapour, for instance, in the presence of an excess or 

 a small supply of oxygen. I believe, therefore, that any con- 

 clusions in regard to temperature and pressure of hydrogen 

 in the stars, deduced from laboratory experiments with 

 electrical discharges in glass vessels, are misleading; since we 

 have to do mainly with phenomena of electrical dissociation, 

 and not alone with those of pressure and apparent tempera- 

 ture — that is temperature which can be measured by calori- 

 metric methods, or which can be calculated from the electrical 

 dimensions of the circuit which is employed. 



It would seem, therefore, that the study of electrical disso- 



