Hinrichs on Dark Lines in the Spectra of the Elements. 37 
Giving the intervals 
Observed, oh toe 24 8 ee 
—- ——~ 
Physical, eet Bt, ee 
These numbers thus confirm the conclusions drawn from the 
calcium spectrum. At the same time there appears yet one most 
remarkable new relation if we compare the interval 40 of ba- 
rium, which interval seems to be a physical one, with the corres- 
ponding interval 60 of calcium. For we have 
Calcium, O= °8 hence 60=—4°8 
Barium, O=1°'1 « 40= 4°4 
or only a difference of 0™™ 000004 in wave-length between 
numbers as large as 0™™-00005. Is this physical interval for 
calcium actually the same as that for barium? Only more accu- 
rate observations can decide it; but if it proves equal, very great 
consequences will flow out of it. 
The magnesium spectrum is represented by Kirchhoff as but 
one briliant group. We have: 
Le ; 0. E. 
Ge 1655°6 58 +8 
oe : 48-8 0-0 
de 847 5 34°8 4 
showing d=7‘0 and conform to the first and second laws (I. and 
II 
Thus the four laws, first found for the calcium spectrum, are 
true for all the members of the group of alkaline earths, as fa: 
as their spectra are known. From this we conclude that they are 
essentially correct for all elements. How far this generalization 
is warranted we will now test by one of the most remarkable 
ectra: the brilliant and rich spectrum of ‘ron, especially the 
three great groups of lines in this spectrum, groups almost with- 
out parallel both in regard to range, intensity, and closeness o 
the lines. Using the same signs as before, we : 
Tron, Group I, d,='8, A, =7d ,=5'6. 
A K. D. 
i. C. E. 
4b ar ae gos cate — 
re oe hel be 178 0 
5d 31:3 86 7 31:4 +1 
4a 39°9 ot 40-2 4.3 
6c 42°6 20 . 42-6 ‘0 
4d 45°6 458 +2 
Intervals, observed, 8:13:17:11:3:4 
—_—o —o_ —_~ 
physical, 21 : 28 : 7 
or, oa, =: 44, °% 4; 
