However, according to (16) it is:
where is the radiation intensity in the resting cavity. Thus it must be
or, since :
This is in agreement with the generally valid theorems of the theory of H. A. Lorentz.
If we set in accordance with the Stefan-Boltmann law
then it follows (see. (14)):
The constant of the Stefan-Boltzmann law is thus to be divided by .
The energy density of the true radiation is:
thus it has the same value as in the resting cavity.
The total energy follows from (17): it has the value:
- See for instance, M. Abraham, Theorie der Elektrizität, II, p. 282 (1905)