338 



indicated by B) is the "//-width" of the line. So R signifies the 

 width an observer would assign to the line if he estimated its 



Fi} in 



I. C 



Fig Sa 



F,g Hh 



.*.rM) 



,;i^» 



Fig. 5a -66. 



boundaries to lie situated at the wave-lengths wliere the relative 

 intensity has the value corresponding to H. (By "relative intensity" 

 we understand the proportion between the intensity at the selected 

 point of the dispersion line and the intensity in the surrounding 

 continuous spectrum). 



Suppose the "//-boundaries" of the line to be situated at ).ji and 

 ).Y, then we obtain from equation (2); 



k k 

 Xii—x,=— — ; ^^ and ;.r— -t, = — 77-^-:; r.>- • (8) 





B + (n,-\y 



2Hk 



(4) 



or, inversely, expressing H in B, 



^=-^^ l/^+K-ir (5) 



We may leave the negative value of the radical out of account. 



Now proceeding to the case of two neighbouring equally strong 

 lines, we prefer to indicate the places in the spectrum by the 

 quantity 



I = }.—Xm 

 (cf. Fig. 5,6) in which 1^ represents the wave-length corresponding 

 to the point halfway between the two absorption lines, so that this 



