132 THE CHEMISTRY OF THE SUN. [CHAP. 



conditions of temperature and pressure, the very complicated 

 spectrum of hydrogen could be reduced in the laboratory to one 

 line in the Hue-green corresponding to F in the solar spectrum ; 

 and also that the equally complicated spectrum of nitrogen is 

 similarly reducible to one bright line in the green, with traces of 

 other more refrangible faint lines. From a mixture of the two 

 gases we obtained a combination of the spectra in question, the 

 relative brilliancy of the two bright green lines varying with 

 the amount of each gas present in the mixture ; and by remov- 

 ing the experimental tube a little further away from the slit of 

 the spectroscope, the combined spectra were reduced to the two 

 bright lines. By reducing the temperature all spectroscopic 

 evidence of the nitrogen vanished ; and by increasing it, many 

 new nitrogen lines made their appearance, the hydrogen line 

 always remaining visible. 1 



These experiments enabled us at once to connect the two 

 series of observations. 



It was only necessary, in fact, to assume that, as in the case 

 of hydrogen and nitrogen, the spectrum became simpler when 

 the density and temperature were less, to account at once for 

 the reduction in the number of the lines visible in those regions 

 where the pressure and temperature of the absorbing vapours of 

 the sun would be reduced. 



The results of the continuation of this line of inquiry will be 

 stated further on. 



3. The Contortion of Lines. 



Those strange contortions which as we have seen are commonly 

 observed in the bright chromospheric lines, and in the dark lines 

 on the disc of the sun, were at first a very great puzzle, not only 

 to me, but to two eminent physicists whom I consulted at the 

 time. The accompanying phenomena, however, soon suggested 

 the explanation which, unknown to me then, had been applied 



1 Proc, Roy. Soc. No, 112, 1869, 



