give rise to a small displacement of tlie absorjilioii line towards 

 the siile of the larger wave-lengths. A shift of this kind has been 

 oi)ser\ed i>y Humphreys and Mohler in their investigation of the in- 

 tlnenee of |)ressiu'e on the position of spectral lines. However, as 

 the formnla (41) does not lead to the laws the two physicists have 

 established for the new phenomenon, I do not pretend to have 

 given an explanation of it. 



Nevertheless we may be sure that in those cases in which the 

 dissymmetry of the Zeeman effect can be detected, the last term in 

 (41), which in fact is of the same order of magnitnde as the expres- 

 sion (38), can have an influence on the position of a spectral line 

 that is not wholly to be neglected. 



On the other hand, it ]iow becomes clear that, in the case of a 

 large value of ij, the term a in (11) may certainly be neglected, its 

 influence on the position of the middle of the line being much smaller 

 than the breadth. ') 



§ 19. We shall conclude by examinmg the influence of the last 

 term in (19), which we have likewise omitted. If we replace /' by 



?« . . m 



/' -| and, in virtue of (10), /' by / -\ — -, which I shall denote by 



t' ' ' T" 



(ƒ'), and if this time we neglect the term «, the formula (11) may 

 again be written in the form (28). Indeed, if we put 



(ƒ') 1 



'»V = ^ ="»'+- (42) 



m T 



we shall have 



§ = '"'(»"»' — «')• 



Instead of (42) we may write 



1 

 «0 = «0 + ^ r (43) 



an equation which shows that the absorption band lies somewhat more 

 towards the side of tlie smaller wave-lengths than would correspond 

 to the frequency n„ and that its position would bo shifted a little, 

 if the time t were altered in one way or another (§ 16). These displa- 



1) Prof. Julius has called my attention to the I'act that in many cases the absorp- 

 tion lines are considerably broadened by the change in the course of the rays that 

 can be produced in a non-iiomogeneous medium by anomalous dispersion. In the 

 experiments of Hallo, I have discussed, this phenomenon seems to have liad no 

 influence. This may be inferred from tlie circumstance that the emission lines of 

 his flame had about the same breadth as tlie absorption lines. 



