CH. xxiv.] YOUNG'S WORK. 327 



us to add laboratory results to the solar ones, has been a careful 

 inquiry into the changes brought about in the spectrum of 

 substances by exposing them to widely different temperatures. 

 In the case of iron our last work has been to note the lines 

 visible when fine iron gauze is burned in the flame produced by 

 a mixture of oxygen and coal gas. The research is a very 

 laborious one, and it may be that some day we shall get a very 

 much better record than that which my assistants and myself 

 have produced ; what we have been able to do we have done 

 over the region of the spectrum already worked over in the 

 spots and flames. 



In any case it is clear that when such facts as these have 

 been studied in the laboratory, we can then compare both solar 

 and laboratory evidence. When these observations are taken 

 into account, we can not only deal with the sun-spot observa- 

 tions comparing them with the spectra of prominences, but 

 with the changes of spectra observed in our laboratories when 

 various temperatures are employed. 



And further, we here limit ourselves to one spectrum, that of 

 iron, for the reason that it has been studied with the greatest 

 care by several eminent observers. In this way we shall be 

 best brought face to face with the actual phenomena, and with 

 very definite statements of facts over a small area. Dolus latet 

 in generalibus. 



Many of the points brought out strongly by the recent spot 

 observations may be gathered, though not certainly in all their 

 fulness, from a comparison of the spot and prominence observa- 

 tions made by Young at Sherman so far back as 1872. I will 

 therefore give them here. I have brought both sets of observa- 

 tions together in the following table, and it will be seen what 

 small relation there is between the intensities of the lines seen 

 in our laboratories and the number of times they are seen, 

 either in spots or storms; while the fact that many lines affected 

 in spots are not seen in prominences, and vice versa, comes out 

 very clearly. 



