222 Trowbridge — Spectra of Hydrogen and the 



Art. XXI. — The Spectra of Hydrogen and the Spectrum of 

 Aqueous Vapor; by John Trowbridge. 



It is customary to consider that there are two spectra charac- 

 teristic of hydrogen — a four-line spectrum, so-called, and 

 another consisting of many lines widely distributed through 

 the spectrum, known as the white spectrum. The four-line 

 spectrum appears when a condenser discharge is employed 

 with what is called dry hydrogen : it is also readily produced 

 in steam and water vapor. From the fact that a condenser 

 discharge seems necessary to excite it in dry hydrogen, it is 

 supposed to indicate a higher temperature than the white 

 spectrum. 



The four-line spectrum is found in the atmosphere of the 

 sun ; and is a characteristic spectrum of certain types of stars. 

 There are also other lines attributed to hydrogen in the stars 

 which are supposed to indicate conditions of pressure and tem- 

 perature which perhaps can be imitated and studied in labora- 

 tories. 



I propose to show, in this paper, that conclusions in regard 

 to temperature and pressure of hydrogen in celestial bodies, 

 deduced from observations on hydrogen enclosed in glass 

 vessels, are untrustworthy ; and that electrical dissociation 

 must be considered as a most important element in determining 

 the characteristics of a gaseous spectrum — more important 

 indeed than the question of pressure and apparent temperature. 



I shall give my reasons for believing that the four-line spec- 

 trum of. hydrogen in the atmosphere of the sun is an evidence 

 of aqueous vapor in that atmosphere and therefore is an evi- 

 dence of the existence of oxygen in the sun. The conviction 

 is forced upon me that the term dry hydrogen is a misnomer, 

 when the gas is subjected in glass vessels to condenser dis- 

 charges or to sufficiently powerful steady currents of elec- 

 tricity. 



The bibliography of the subject of the spectra of hydrogen, 

 is so extensive that I must, with due regard to the limits of 

 this article, refer the reader to the reports of the committee of 

 the British Association, and to the recognized bibliographical 

 authorities on this subject, and I do this because I feel that in 

 my experiments I have exceeded the experimental limits of 

 previous investigators ; for I have been enabled to employ 

 more powerful electrical discharges than have been hitherto 

 possible. My work, therefore, does not trench in this respect 

 upon that of previous investigators. 



