745 
to the motions with wave-lengths beneath A has the same magnitude 
as that belonging to wave-lengths beyond 4. This is expressed by 
the equation 
i d?. 1 1 d) 
i 2he pn in 2he 46” 
eles | do Piven it 
or if we put 
2he 2he 2he 
Ed, — == Ba ey ee 48} 
had ka, 1 kà'1 
by 
di Xo 
ada 1 ede 
et—l 2.) etl 
0 0) . 
From this equation we can derive by suitable approximations 
for each «x, the corresponding 2’. If now we consider a gas of 
definite density, d and therefore 2, are given and we can determine 
the value of «, for each temperature 7. It is true that the second 
of the equations (8) does not suffice for this, as c depends, in the 
way indicated by (7), on M, which is a complicated function of 7’. 
But Lenz gives the formula 
45 
: O (ada 
gh Serta, wos per <0) 
0 
which can be used to determine «,. The quantity 
18ah’? 
Qo — (11) 
is a certain temperature which can be indicated for each gas as 
soon as its density is given. After having chosen 7’, we find #, from 
(10), x’ from (9) and finally 4’ from the relation 
Nr 
mk, 
MN - a J ts 5 À F 2 ° A e (12) 
following from (8). 
Let us consider as an example helium of the density corresponding 
to 0° C. and 1 atm. Then @ = 7° and according to (10) z, =1, if 
— == 0,22; for we have 
oO 
