( 281 ) 
Fraunhofer lines must show certain systematic distinctions as compared 
with the character of pure absorption lines. 
Dispersion bands, produced by the solar atmosphere, must be 
asymmetrical, the narrower ones to a higher degree than the wider ones. 
Indeed, we may represent the refracting power of that atmosphere 
for each kind of R-light appertaining to a given line, by the expression: 
(R,„ A m ) R = (RA)r + A„)r 
in which the term R, A x relates to the constituent of the atmosphere 
producing the line in question, and R 0 A 0 means the refracting power 
of the mixture of the remaining constituents. Both terms are positive. 
In a similar expression, concerning the V-light of the same line: 
(R m A w )v = (RA)v + 
the term ( R 0 A 0 )v will not differ to any appreciable degree from 
(R, A # )r; but now R l is negative. At equal distances on either side 
of the absorption line, R x has (according to the law of anomalous 
dispersion) nearly equal values of opposite sign. If, therefore, we 
select on the violet side of the line a wavelength, matching the 
first-chosen R-light symmetrically, we may write: 
{R,n )v— - (R, AJr + (R» A.)r, 
so that, with such pairs of wave-lengths, the relation holds: 
(Rm A* )u + (Rm A m )v = 2 R 0 A 0 = const. 
Suppose we approach the line from both sides in a symmetrical 
way, then (R„*A„)ft and (R in A m )y begin with being positive; one 
increases, the other decreases, and when (R to A,„)r has reached the 
value 2R 0 A 0 , (R m L m ) v passes zero, and is going to take increasing 
negative values. But in absolute magnitude (R,«A m )v will always be 
inferior to the corresponding (R m A ot )r ; the difference grows from 
0 to 2R 0 A 0 , and then remains constant when we approach nearer to 
the absorption line. 
Figure 8 serves to elucidate this. The ordinates a and a', b and b' 
etc. represent values of Rm A w , bearing upon waves that are sym¬ 
metrically situated with respect to the absorption line. The ordinates 
of the dotted line have the nearly constant value R 0 A 0 . 
The degree to which the light is dispersed by refraction in the 
solar gases, is determined by the absolute magnitude of R m A m ; so 
the average effect must be greater on the red side of an absorption 
line than on the violet side. The asymmetry of the dispersion band 
must manifest as a displacement of the Fraunhofer line towards the 
r ed. If however the terms ± R, A x are highly predominating in a 
rather wide band of the spectrum, in other words, if the vibrating 
systems which give rise to our line constitute an important part of 
