THE STRUCTURE OF THE SERIES OF LINE- AND BAND-SPECTRA. 597 
decrease again. In the even rows 4 and 6, on the other hand, there is a rapid decrease 
from column I. to column II. 
Now, by a course of reasoning upon which I shall not enter here, I have been led 
to investigate a phenomenon which curiously shows the same regularities, although at 
first sight it may appear difficult to perceive its causal connection with the changes of 
our constants. I refer to the effects of pressure on the displacements of the spectral 
lines. If we take these displacements from the results of HumpHrey and MoH.eEr’s 
well-known researches and arrange them in MENDELEJEF’s system, we obtain the 
following table of values, in which the displacements are given in 7,5 th of a tenth- 
metre, and correspond in each case to a change of pressure of 12 atmospheres : 
I. II. III. IV. Vid lh ole VII. VIII. 
<= = ————— | 
1 
2 
Na Mg Al Si 
3 25 46 55 43 
K Ca Vi V Cr Mn Fe Ni Co 
4 130 27/54 19 25 26 23 25 28 24 
Cu Zn As 
5 33 57 35 
Rb Sr Y Zr Nb Mo Rh Pd 
6 130 37/65 15 28 34 40 30 33 
Ag Cd In Sn Sb ; 
af 39 80 88 55 49 | 
Cs Ba La Ce 
8 160 34/58 32 27 | 
9 
\ W Os Pt 
10 19 19 20 
| Au Hg Tl Pb Bi 
11 49 81 61 60 49 
Hvidently these figures show the same features as the values of = discussed before. 
1 
The amplitude of the changes is again decidedly greatest in column J., and decreases 
rapidly, being quite insignificant in columns VII. and VIII. We notice further that 
in the odd horizontal rows 8, 5, 7 and 11 the displacements tend from small values 
towards a maximum and decrease afterwards, whereas the even rows 4, 6 and 8 begin 
with high figures, which diminish rapidly and asymptotically approach a constant 
minimum value. It is also worth mentioning that those cases where two kinds of 
displacements have been observed by Messrs Humpurey and Moats, e.g. Ca, Sr, and 
Ba, belong to this second class. Are we allowed, then, to conclude that a connection 
exists between the displacements of the lines through changes of pressure and the 
constants a, of the Rypserc-THIELE equation? Obscure and seemingly unfathom- 
able as these phenomena are at present, they cannot but open new vistas of thought 
and instigate theoretical research. 
