102 INORGANIC EVOLUTION. [CHAP. 



(3) From experiments with mixtures of metallic vapours and gases 

 it came out that the longest lines of the smaller constituent remained 

 visible after the shorter lines had disappeared, the spectrum of each 

 substance present getting gradually simpler as its percentage was 

 reduced,* the shorter lines being extinguished gradually. Shortly 

 .alter these observations were made, I included among some general 

 propositions :f "In encounters of dissimilar molecules the vibrations of 

 each are damped." 



(4) The various widths of the lines, especially of the winged longest 

 ones, were found to depend upon pressure or density, and not tem- 

 perature. J 



(5) The " longest lines " of any one metal were found to vary in 

 their behaviour in most extraordinary fashion in solar phenomena, 

 being furthermore differentiated from the shorter ones ; and on this 

 -and other evidence, I founded my working hypothesis of the dissocia- 

 tion of the chemical elements at the solar temperature. In 1876 I set 

 out the facts with regard to calcium. 



(6) In 1883, Professor W. Vogel, in a friendly criticism, pointed 

 out the evidence, then beginning to accumulate, that under certain cir- 

 cumstances the wave-lengths of lines are changed. In 1887, I extended 

 this evidence,|| and I think it w^as I who coined the word " shift " to 

 express these changes. U 



I now pass on first to the results which Mr. Jewell claims to have 

 established. 



With the enormous dispersion produced by the instruments referred 

 to, it is found that certain metallic lines, but not all, are displaced or 

 " shifted " towards the violet when compared with the corresponding 

 ;solar lines. " There was a distinct difference in the displacement, not 

 only for the lines of different elements, but also for the lines of dif- 

 ferent character belonging to the same element." 



The " different character " above referred to turns out to relate 

 not so much to the intensity as to the length of the line, and, asso- 

 ciated with this, its reversibility ; the longest lines are the most dis- 

 placed, the shortest, least. 



Further, in the spectrum of the arc itself, the position of a line with 



* Phil. Trans. (1873), p. 482. 



f Studies in Spectrum Analysis (1878), p. 140. 



t Phil. Trans., 1872, p. 253. 



Nature, vol. xxvii (1883), p. 233. 



|| Chemistry of the Sun, p. 369. 



1[ Since the parentage is uncertain, I may say that perhaps "shiftings" would 

 Tiave been a better word, as shift is otherwise employed, e.g., Love's last shift 

 ^translated by a French author, la derniere chemise de V amour). 



