of the Spectral lines of the Elements. 213 
lengths determined by interpolation, it must be borne in mind 
that each wave length is calculated by means of a formula, the 
constants of which are determined from a number of measured 
distribution of the lines corresponding to any one element is 
subject to any definite law. The solution of this problem was 
first attempted by Mr. Hinrichs,* who, from data in my judg- 
ment far too limited in number, drew the conclusion that the 
spectral lines in the case of any element are distributed in 
hice the lines belonging to any one group being equidistant. 
8 would probably bring the whole subject within the reach 
of Wrede’s theory of absorption,} which is a special application 
_ of the principle of interferences. My own study of the sub- 
_ ject does not justify the conclusion to which Mr. Hinrichs ar- 
tived. Even a cursory examination of the tables of wave 
Se Mr SE ee ee a ee ee a eer tere 
Tor in measuring the wave lengths. As the differences in wave 
h measure the distances between the lines, the element of 
again due to Mr. 8. Se 
sisted in the whole of my la- 
aT aft oil h demand the fullest 
