What We Learn from the Sun 



They examined the spectra of the light from 

 incandescent substances (white-hot metals and 

 the like), and found that in these spectra there 

 are no dark lines. 



They examined the spectra of the light from 

 the stars, and found that these spectra are 

 crossed by dark lines resembling those in the 

 solar spectrum, but differently arranged. 



They tried the spectra of glowing vapours, and 

 they obtained a perplexing result. Instead of a 

 number of dark lines across a rainbow-tinted 

 streak, they found bright lines of various colour. 

 Some gases would give a few such lines, others 

 many, some only one or two. 



Then they tried the spectrum of the electric 

 spark, and they found here also a series of bright 

 lines, but not always the same series. The 

 spectrum varied according to the substances 

 between which the spark was taken and the 

 medium through which it passed. 



Lastly, they found that the light from an incan- 

 descent solid or liquid, when shining through 

 various vapours, no longer gives a spectrum with- 

 out dark lines, but that the dark lines which then 

 appear vary in position, according to the nature 

 of the vapour through which the light has passed. 



Here were a number of strange facts, seemingly 

 too discordant and too perplexing to admit of 

 being interpreted. Yet one discovery only was 

 wanting to bring them all into unison. 



In 1859 Kirchhoff, while engaged in observing 

 the solar spectrum, lighted on the discovery that 

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