OXYGEN IN THE SUN. 3 



length of the spectrum that is, some red, some orange, 

 some yellow, and so on. In the solar spectrum corres- 

 ponding dark lines are found along the whole length of the 

 spectrum that is, some in the red, some in the orange, 

 yellow, etc, and precisely in those parts of these various 

 spectral regions which the bright lines of glowing iron would 

 occupy. Multitudes of other dark lines exist of course in 

 the solar spectrum. But those corresponding to the bright 

 lines of glowing iron are unquestionably there. They are 

 by no means lost in the multitude, as might be expected ; 

 but, owing to the peculiarity of their arrangement, strength, 

 etc., they are perfectly recognizable as the iron lines reversed, 

 that is, dark instead of bright Kirchhoffs researches 

 showed how this is to be interpreted. It means that- the 

 vapour of iron exists in the atmosphere of the sun, glowing 

 necessarily with an intensely bright light ; but, being cooler 

 (however intensely hot) than the general mass of the sun 

 within, the iron vapour absorbs more light than it emits, 

 and the result is that the iron lines, instead of appearing 

 bright, as they would if the iron vapour alone were shining, 

 appear relatively dark on the bright rainbow-tinted back- 

 ground of the solar spectrum. 



Thus was it shown that in the atmosphere of the sun 

 there is the glowing vapour of the familiar metal, iron ; and 

 in like manner other metals, and one element (hydrogen) 

 which is not ordinarily regarded as a metal, were shown to 

 be present in the sun's atmosphere. In saying that they 

 are present in the sun's atmosphere, I am, in point of fact, 

 saying that they are present in the sun ; for the solar atmo- 

 sphere is, in fact, the outer part of the sun himself, since a 

 very large part, if not by far the greater part, of the sun's 

 mass must be vaporous. But no other elements, except the 

 metals iron, sodium, barium, calcium, magnesium, alumi- 

 nium, manganese, chromium, cobalt, nickel, zinc, copper, 

 and titanium, and the element hydrogen, were shown to be 

 present in the sun, by this method of observing directly the 

 solar dark lines. In passing, I may note that there are 



