OXYGEN IN THE SUN. 19 



limited area upon the disc or margin of the sun, but the 

 spectrum of light from the whole disc." 



In support of the important statement here advanced, 

 Dr. Draper submits a photograph of part of the solar spec- 

 trum with a comparison spectrum of air, and also with some 

 of the lines of iron and aluminium. The photograph itself, 

 a copy of which, kindly sent to me by Dr. Draper, lies before 

 me as I write, fully bears out Dr. Draper's statement It is 

 absolutely free from handwork or retouching, except that 

 reference letters have been added in the negative. It shows 

 the part of the solar spectrum between the well-known 

 Fraunhofer lines G and H, of which G (an iron line) lies in 

 the indigo, and H (a line of hydrogen) in the violet, so that 

 the portion photographed belongs to that region of the 

 spectrum whose chemical or actinic energy is strongest 

 Adjacent to this lies the photograph of the air lines, showing 

 nine or ten well-defined oxygen lines or groups of lines, and 

 two nitrogen bands. The exact agreement of the two 

 spectra in position is indicated by the coincidence of bright 

 lines of iron and aluminium included in the air spectrum 

 with the dark lines of the same elements in the solar spec- 

 trum. " No close observation," as Dr. Draper truly remarks, 

 " is needed to demonstrate to even the most casual observer" 

 (of this photograph) " that the oxygen lines are found in the 

 sun as bright lines." There is in particular one quadruple 

 group of oxygen lines in the air spectrum, the coincidence 

 of which with a group of bright lines in the solar spectrum 

 is unmistakable. 



" This oxygen group alone is almost sufficient," says Dr. 

 Draper, "to prove the presence of oxygen in the sun, for not 

 only does each of the four components have a representative 

 in the solar group, but the relative strength and the general 

 aspect of the lines in each case is similar.* I shall not 



* Dr. Draper remarks here in passing, " I do not think that, in 

 comparisons of the spectra of the elements and sun, enough stress has 

 been laid on the general appearance of lines apart from their mere 

 position ; in photographic representations this point is very prominent. " 



