XI.] EVIDENCE AFFORDED BY THE SHIFTING OF LINES. 103 



but little material present " was approximately the same as the posi- 

 tion of the line when reversed." Now since the longest lines are most 

 displaced to the violet, this means that the smaller the quantity of 

 a substance present the greater is the displacement towards the violet ; 

 and, therefore, the greater the quantity present, the greater the dis- 

 placement towards the red. 



Mr. Jewell found that " with an increase in the amount of the 

 material in the arc there was an increasing displacement of the line 

 towards the red," and then that, " unless the line became reversed, all 

 further progress in that direction ceased." 



Here is an observation regarding the red line of cadmium. " It 

 was found that if the micrometer wires were set upon it with very 

 little cadmium in the arc, then as the amount was increased the line 

 almost bodily left the cross-hairs, always moving towards the red." 



Mr. Jewell considers he has established that the vibration-period 

 of an atom depends to some extent upon its environments. " An 

 increase of the density of the material, and presumably an increase of 

 pressure, seemed to produce a damping effect upon the vibration 

 period." My result of 1872 with regard to pressure was endorsed, 

 " the new results are found to be due to pressure and not temperature." 

 We seem, then, now to be in presence of two damping effects in the 

 case even of metallic lines, one which extinguishes lines when we deal 

 with dissimilar molecules, and one which changes their wave-length 

 towards the red when we deal with similar molecules. 



A carefully prepared table showed the origin, intensity and 

 character of the solar lines considered, the intensity and character of 

 the corresponding metallic lines, the wave-lengths of both, and the 

 observed displacement. 



Many references to solar phenomena were made by Mr. Jewell in 

 relation to his work, but I do not propose to discuss them here. There 

 is one point, however, I must refer to. He considers that the conclu- 

 sions to be drawn from a study of the new shifts " effectually disposes 

 of the necessity of any dissociation hypothesis to account for most 

 solar phenomena." I have already pointed out that this was Professor 

 W. Vogel's conclusion with regard to possible shifts, so far back as 

 1883. 



It is quite easy. " Two adjacent lines of iron, for instance, may 

 show the effects of a violent motion of iron vapour in opposite direc- 

 tions, in the neighbourhood of spots, or one line (the smaller one cor- 

 responding to one of Lockyer's * short lines ') may show a broadening 

 and increase of intensity in the spectrum of a sun-spot, while the 

 other line (the larger one corresponding to one of Lockyer's ' long 

 lines ') is unaffected. But this does not prove that iron vapour is dis- 



