32 Hinrichs on Dark Lines in the Spectra of the Elements. 
As it is well known that some —— American experi- 
menters are engaged in a more accurate and se ba survey of 
possible be further developed. 
It might seem that such an investigation could not lead to 
definite results, since Kirchhoff’s scale is entirely arbitrary and 
even changing. But within a small range equal differences on 
this scale must correspond to equal differences in wave length, 
for whatever the curve may be (we have found it to coincide with 
a parabola), representing the wave-length as a function of Kirch- 
hoff’s millimetre-scale, within such narrow limits the curve will 
coincide with its tangent. We must therefore first see whether 
the different groups of lines exhibit any order. 
ommencing with the Calcium-spectrum, we find a group of 
lines near Fraunhofer’s G. Representing the intensity by I, the 
scale-division by K, the successive differences by D, we find 
from Kirchhoff’s table— 
Group I, d,=5°0. 
1 K 
; D. i. C. E. 
5¢ 2869°7 5-0 1 2869°7 0 
4b 64-7 10-0 2 64°7 0 
4 54°7 20°5 4 54:7 
5¢ 34°2 34°7 5 
It is plain that the values of D are as 1: 2:4; considering 
these ratios as intervals, 2, and calculating from them and the 
difference the values C, which would correspond to a perfectly 
regular distribution of the lines, we obtain the error of this 
theoretical determination H=C—K, as given in the last column. 
We see, the error is almost nothing—the last one might easily 
be conceived as the result of the increased range. Hence we 
find that this group is very regular, having a principal difference 
of 5:0, or a simple multiple (here successive duplication) thereof. 
e second group, stretching from 2653‘2 mm. to 2605°8 mm., 
has a range of 47-4 mm., which appears to be rather large; yet 
we find (comparing lines of high and similar intensity, those of 
lower intensity not being uniformly given): 
Group Il, d,==2-026. 
L K. D. i C. EK. 
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