SECT. iv. THE SUN'S LUMINOUS ATMOSPHERE. 151 



iron and nickel coincide with dark lines in the solar 

 spectrum, he reversed them by sending Drummond's 

 light through their respective flames, thus proving that 

 the coloured flames of these six metals are subject, like 

 the sodium light, to the law of exchanges. 



M. Kirchhoff infers by analogy that the vapours of 

 all these six metals exist in the luminous atmosphere 

 of the sun, and that they absorb and change into heat 

 such rays of the continuous light of the incandescent 

 solar globe as have the same refrangibility with their 

 own, so that the corresponding dark rayless lines on 

 the solar spectrum are the reverses of the bright lines 

 in the spectra which these vapours would give were it 

 not for the brighter light of the sun shining through 

 his luminous atmosphere. 



The dazzling white light of the incandescent body of 

 the sun containing rays of all refrangibilities would give 

 a continuous spectrum shaded with all the seven colours, ( 

 but for his luminous absorbent atmosphere, which comes) 

 like a veil between him and the earth, and crosses his-' 

 spectrum with thousands of dark lines, which are the 

 reverses or negatives of the bright lines in the spectra 

 of the innumerable vapours it contains, all of which must 

 doubtless be the gases of substances existing in the solar 

 mass itself and vaporized by his intense heat. 



Every metal, and almost every elementary substance 

 in a state of gaseous combustion, gives its own peculiar 

 luminous lines to its spectrum, but no volatilized matter 

 can be proved to exist in the sun's atmosphere except 

 such as have bright lines in their spectra coincident 

 with some of its dark lines. 



The bright lines in the spectrum of iron, coincident 

 with the dark lines of the solar spectrum, are so nume- 

 rous that many yet remain unknown. M. Kirchhoif 

 counted seventy in the small space between Fraun- 

 hofer's lines D and F, in which the coincidence extends 



