353 
we desire to emphasize is that they are suggestive of strong absorp¬ 
tion bands, most of them in accessible regions of the spectrum; 
hence by experimental proof or disproof 1 ) the validity of the v A- 
law can indirectly be tested 2 ). 
§ 27 . In the present section we shall apply the results pre¬ 
viously obtained to the elucidation of an important point in the 
general theory. In § 11. we have defined a quantity F and have 
written down the expression of F according to various theories. 
We can now compute (in certain definite cases) the individual terms 
contained in (3), (4), (5) and (9), § 11.; we shall thus get an idea 
of the comparative importance of these terms. Leaving aside G we 
have to calculate four quantities viz.: — 
w 0 2 , ^ 2 , C 2 and ^7ie 2 N/m. (1) 
We take the second term to be directly given; the value of the 
third we borrow from the Kinetic Theory of Gases; the first and 
the fourth we calculate by means of the formulae 
n 
2 
0 
4 Ji 2 c 2 D 
mm 5 
71 
e 2 N 
m 
4 n 2 c 2 
~T~ 
( 2 ) 
(see § 15.). Let us consider a) hydrogen b) carbon dioxide, both 
at 0° C., and 760 millims. We assume for them (§§ 16. and 21.) 
a) D = 11033,5; A = 8,343.10~ 7 cm 2 
b) D = 3394,3; A = 2,145.10~ 7 cm 2 
Let us suppose we are dealing with wave-lengths ranging from 
3,6.10~ 5 cm. to 86,9.10 -5 cm. We find: 
9 Messrs Cuthbertson and Metcalfe have found that (e . g.) the vapour of tellu¬ 
rium exhibits a strong absorption band in the violet ; no absorption, however, 
was observed in the case of zinc. For other observations see Kayser’s Handbuch 
der Spectro s copie, Vol. 3 ., p. 317—336; the evidence is not of a conclusive 
character. 
2 ) In the case of nitric oxide NO we should expect X Q to be about 0,81 ; this 
value follows from (1) if we take a = 5 and if we accept Mascart’s value of the 
refractive index for sodium-light. Now this value of X 0 seems to be contradicted 
by Kreusler’s photoelectric measurements of the NO absorption (Annalen d. 
Physik, Bd. 6., p. 412. 1901). Probably then N O is another case in which the 
■tfA-law does not hold. 
