324 THE CHEMISTRY OF THE SUN. [CHAP. 



The disappearance of the lines of iron, nickel, and titanium, 

 and the appearance of unknown lines as the maximum is 

 reached is shown by curves in Fig. 107 given on the next page. 



The important results thus obtained from the preliminary 

 discussion of the whole of the 700 spots enable us to see that 

 the strange changes noted in the second series (see page 315) 

 were but the indications of the effects of a general law which 

 connects the lines affected in spots with the sun-spot period, and 

 obviously with the varying temperatures proper to each phase of 

 the period. 



Hence we may now generalise the last six statements given 

 on page 316 as follows : 



12. The most widened lines in sun-spots change with the 

 sun-spot period. 



13. At and slightly after the minimum, the lines are chiefly 

 known lines of the various metals. 



14. At and slightly after the maximum, the lines are chiefly 

 of unknown origin. 



15. On the hypothesis under discussion the change indicates 

 an increased temperature in the spots at the sun-spot 

 maximum. 



The results, in my opinion, amply justify the working 

 hypothesis as to the construction of the solar atmosphere 

 given in chapter xxii. 



I am quite content, therefore, to believe that iron, titanium, 

 nickel, and the other substances very nearly as complex as we 

 know them here, descend to the surface of the photosphere, in 

 the downrush that forms a spot at the period of minimum ; but 

 that at the maximum, on the contrary, only their finest con- 

 stituent atoms can reach it. It may also be remarked that 

 these particles which survive the dissociating energies of the 

 lower strata are not the same particles among the constituents 

 of the chemical elements named which give the chromospheric 

 lines recorded by Tacchini, Kicco, and myself. 



