OXYGEN IN THE SUN. li 



oxygen can be readily seen. " The bright lines of oxygen 

 in the spectrum of the solar disc have not been hitherto per- 

 ceived, probably from the fact that in eye-observation bright 

 lines on a less bright background do not make the impression 

 on the mind that dark lines do. When attention is called 

 to their presence they are readily enough seen, even without 

 the aid of a reference spectrum. The photograph, however, 

 brings them into greater prominence." As the lines of 

 oxygen are not confined to the indigo and violet, we may 

 fairly hope that the bright lines in other parts of the spectrum 

 of oxygen may be detected in the spectrum of the sun, now 

 that spectroscopists know that bright lines and not dark 

 lines are to be looked for. 



Dr. Draper remarks that from purely theoretic considera- 

 tions derived from terrestrial chemistry, and the nebular 

 hypothesis, the presence of oxygen in the sun might have 

 been strongly suspected ; for this element is currently stated 

 to form eight-ninths of the water of the globe, one-third of 

 the crust of the earth, and one-fifth of the air, and should 

 therefore probably be a large constituent of every member 

 of the solar system. On the other hand, the discovery of 

 oxygen, and probably other non-metals, in the sun gives 

 increased strength to the nebular hypothesis, because to 

 many persons the absence of this important group has pre- 

 sented a considerable difficulty. I have already remarked 

 on the circumstance that we cannot, according to the known 

 laws of gaseous diffusion, accept the reasoning of those who 

 have endeavoured to explain the small density of the outer 

 planets by the supposition that the lighter gases were left 

 behind by the great contracting nebulous mass, out of which, 

 on the nebular hypothesis, the solar system is supposed to 

 have been formed. It is important to notice, now, that if 

 on the one hand we find in the community of structure 

 between the sun and our earth, as confirmed by the dis- 

 covery of oxygen and nitrogen in the sun, evidence favouring 

 the theory according to which all the members of that system 

 were formed out of what was originally a single mass, we do 



