226 Trowbridge — Spectra of Hydrogen and the 



ture of sixty inches. The dispersion was small on account of 

 the small number of lines to the inch ; but it had the advantage 

 of exhibiting the salient features of the spectra on one plate, 

 with a dispersion of the order used by astrophysicists ; and 

 thus enabled comparisons to be readily made. The distance 

 between the great H lines in the second spectra was approxi- 

 mately 2 mm . The camera was on an arm pivoted at half the 

 distance between the slit and the grating. This arrangement 

 was adopted for compactness. The grating and camera were 

 enclosed in a light-tight box and a lever enabled me to expose 

 the plate when this box was closed. 



Yarious liquid resistances were employed to 2'egulate the 

 strength of the electric current. I finally used distilled water, 

 which was kept running through glass tubes. Since my object 

 was not to measure the current, but rather to keep it within 

 safe limits, I did not find it necessary to employ cadmium 

 terminals in a solution of iodide of cadmium. The direct 

 battery current gave me the white type of hydrogen spectrum, 

 while the second type was given by the powerful condenser 

 discharges. A revolving drum provided with suitable metallic 

 strips enabled me to safely charge and discharge the condensers 

 through the spectrum tubes. 



In working with powerful condenser discharges I found that 

 I obtained essentially the same spectrum whether the tube was 

 filled with hydrogen, rarified air or nitrogen, notwithstand- 

 ing the great care taken in heating the tubes and drying the 

 gases ; this characteristic spectrum was that of water vapor — 

 containing lines of hydrogen and of oxygen — with traces of 

 nitrogen lines. 



The employment, therefore, of a condenser discharge in 

 glass tubes drives off aqueous vapor from the glass walls, 

 even if extraordinary care is taken to expel such vapor in the 

 process of exhausting such tubes. My experiments entirely 

 confirm Professor Crookes' statement on this point. Glass 

 seems to be of a permeable nature, and in the process of 

 manufacture is doubtless filled with gases which reveal them- 

 selves when disruptive electrical discharges are employed. It 

 does not seem possible that dry hydrogen can exist as such in 

 a tube when it is subjected to a condenser discharge ; and I 

 therefore believe that the spectrum of hydrogen called the 

 four-line spectrum is an evidence of the presence of aqueous 

 vapor, for it can be produced with the greatest ease when we 

 are certain that this vapor is present. This spectrum, to my 

 mind, is an evidence of the presence of oxygen in the sun's 

 atmosphere. 



The true spectrum of hydrogen seems to be the white 

 spectrum. This is developed by a steady current which should 



