344 



Ik 



from which follows 



L = ^^^ (15) 



B\/N ^ ' 



In case we are dealing witii tico iieighbonring lines of eqnal 



strength (that is: equal value of — J at distance 2A from each 



other, it is convenient to indicate all places in the speclrnm (like 

 we did on p. 338) by a new system of abscisses : 



Z=^ -;,.,ƒ . (16) 



Ay representing the wave-length of the point midway between the 

 absorption lines, wliere we place the zero of our scale of /-values. 

 The abscisses of the two absorption lines are now — A and -\- A. 

 According to the equation h =^ 2 h; of p. 335, and considering 

 the smaliness of the selected spectral region, the distribution of the 



Iiglil in it will entirelj' depend on the quaMlity — — 1- 



as a function of k or of /. Applying (13) and (16) we find 



A\ ^ N, iV,(A-/,)= iV,(A-/,)' N,il + Ay^NAl-Ar^ 

 The L-boundaries of each of the components of the pair are 



4X,-' 

 obtained by making (17) eqnal to Z' or, after (15), to — — . Let us 



consider the red-facing component. Its L-l)onndaries are situated at 

 /=//? and l=l\', and can be deduced from (17). According as the 

 -f- or the — sign is taken, we obtain 



iR or lv=-\X '+^±|/l6~ + l . . . (18) 



The two negative values of the same radical quantities represent 

 //? and ly of the vio/et-facing component of the pair. 



^ 7. Diffusion lines in the spectrum of the Umh of the solar disk. 



(n i)' 



At the limb a smaller value L" of — -— will suffice to bring 



about the same degree of darkening that Z' gave in the centre. 



The "L'-boundaries" determine a width B' through the relation 



2 k 

 L' ^= —- rr, i'l analogy with (15). We thus find tor the borders 



B' y N 



