( 886 ) 
parison with ge. Even within the region of strong absorption, the 
term d is of litthe consequence. Let us for instance consider the 
frequency where «= ‘*/,»'. There the ratio of the second to the 
third term is 
Vis Bites? tE Ea TD gga DE 
There are no experimental data at my disposal from which the 
values of x might be deduced for calcium vapour; but for sodium 
vapour the maximum value of nx was found to be 103), which, 
at the indicated spot of the spectrum, makes nx = 5 X 10-4, and, 
IX 2,5 x 10-4. For greater values of 2a 
the said ratio decreases rapidly. So the second term of the second 
member of (8) may be neglected. 
But in the denominator of the third term we meet with the 
variable factor ‘/, (7 + n,), where in (6) the constant factor 7, occurs. 
It follows from this circumstance that now the dispersion curve does 
consequently, */,x = 
not show the perfect svmmetry of the one which represents equation 
(6). The character of the deviation becomes apparent from equation 
rc 
(/ 
1/, ov'%, we write: 
s 
) if, omitting the term 
bo 
ou 
v, (Au? Hw) 
With respect to the point of intersection 
P of the horizontal line n,’ (fig. 2) with 
ZZE re 
No 
the vertical line u =O the curve represent- 
ing 7° is symmetrical. Let us now suppose 
n, = 1, then the line n, coincides with the 
line n,*. Constructing, in the same figure, 
the curve whose ordinates are the square 
roots out of the ordinates of the first curve, 
we immediately see, that the “anomaly” of 
the index of refraction 7 is greater on the 
violet than on the red side of the line. It 
= =, Ìs questionable whether absorbing vapours 
Fig. 2. will present cases in which this difference is 
great enough to show itself in the observations. 
Dhn a a Ao aten tach - - atd 
ma 
§ 4. On the nature of the damping parameter. — A permanently 
acting cause why the vibrations of an electron die out, is the fact 
that it radiates waves in all directions, thus “scattering” its kinetic 
energy. An electron, moving with the variable velocity v, experiences 
a force due to its own field, opposite to its acceleration, and, in 
ll W. Vorer, |. e. p. 142. 
