334 
Let us apply equation (3), § 15., to a wave-length lying far 
beyond the limits of the visible spectrum: John Koch has found 1 ) 
for X = 86,9 ... v= 1,0001373. 
For this value of X, equation (3), § 15., gives 
with values (1) of the constants ... v = 1,0001401 
.(2). y 1411 
.(3). 1360 
The observed value lies between the calculated ones. Inversely, if 
we assume 
a) X = 5,893 ... v = 1,0001400 2 ) 
b) 86,9 . . . 1373 
we find, applying the equation, 
(4) D = 10924 A = 7,88. 
The dispersion of hydrogen has been recently investigated by 
K. Scheel 8 ). With the omission of three results (which on account 
of their obvious irregularity are useless for our purpose) Scheefs 
data run as follows 
( 5 ) 
a) X = 4,358 
b) 4,712 
c) 4,922 
g) 5,780 
h) 6,676 
v = 1,0001406 
1398 
1396 
1389 
1376 
From (a) and (h) we 
deduce: A — 7,70 
... ( b ) and (h) 
7,59 
. . . (c) and (Ä) 
8,29 
... (a) and (g) 
5,75 
mean 7,52 
Scheel has shown that the results of his experiments on the dis¬ 
persion of hydrogen (and of two other gases, see below) can be 
represented by expressions of the form 
9 Annalen d. Physik, Bd. 17 -, p. 665. 1905. 
2 ) This is the average value deduced from observations by Ketteler, Lorenz, 
Perreau, Mascart and G. W. Walker. 
3 ) Verhandlungen d. d. phys. Gesellschaft, Jahrg. 9, p. 21. 1907. 
