Hydrogen and the Spectrum of Aqueous Vapour. 339 



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 tempera- 

 ture. I shall give my reasons for believing that the four- 

 line spectrum of hydrogen in the atmosphere of the sun is an 

 evidence of aqueous vapour in that atmosphere, and therefore 

 is an evidence 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 con- 

 denser-discharges, or to .sufficiently powerful steady currents 

 of electricity. 



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 Committees 

 of the British Association on the subject of Spectrum Analysis, 

 and to the recognized 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. 



The source of the electrical energy 1 employed was twenty 

 thousand storage-cells of the Plante type. The direct current 

 from these cells, through a liquid resistance, was used to 

 produce the white spectrum ; and a glass condenser consisting 

 of 300 plates of glass, each plate having a coated surface of 

 16 X 20 inches, with a total capacity of about 18 microfarads, 

 was charged by the cells to produce the four-line spectrum, 



I had great difficulty at first in obtaining tubes which would 

 stand such powerful discharges. I began my work with end- 

 on tubes, which were closed by plates of quartz luted on with 

 silicate of soda. The electrodes were hollow cylinders of 

 aluminium connected to thick pieces of platinum wire. 

 These wires passed through the walls of the glass tubes and 

 were immersed in large vessels of distilled mercury. After 

 considerable experience, tubes were constructed which would 

 resist the disruptive and heating effect of the discharges. 

 This form of tube, however, was abandoned for another shown 

 in fig. 1. The chief peculiarity of this form of tube was an 

 <c-ray bulb in place of the end covered with a quartz plate. 

 The reason for the adoption of this form of tube is this : — it 

 was necessary to heat the entire tube to a high temperature 

 for a long period during the process of exhaustion to drive 

 out the air and aqueous vapour before it was filled, with 

 hydrogen ; and this heating was impossible with a tube having 

 a luted-on end. Moreover, the thin glass of the bulb did not 



