92 H. Draper—Discovery of Oxygen in the Sun. 
The reason I did not use air in an exhausted Pliicker’s tube 
spectrum. In Pliicker’s tubes with a Leyden spark the nitro- 
gen lines are as plain as those of oxygen here. As faras I have 
seen oxygen does not exhibit the change in the character of its 
- lines that is so remarkable in hydrogen under the influence of 
pressure as shown by Frankland and Lockyer. 
The bright lines of oxygen in the spectrum of the solar dise 
have not been hitherto perceived probably from the fact that 
in eye-observations bright lines on a less bright background do 
not make the impression on the mind that dark lines do. 
gives increased strength to the nebular hypothesis, because to 
any persons the absence of this important group has presented 
