Friedrich Hasenöhrl

“ With the aid of equations (2) and (10) , momentum and total energy () can be expressed by the state variables of the resting system. (We have to consider here, that equations (1) , (3) , (4) and (5) may not be applied now; they only hold for velocity changes at constant volume.) ”

“ A specific electromagnetic momentum is connected to radiation in a moving cavity. Because the heat content of each body partly consists of radiating energy, each body has a specific electromagnetic mass that depends on its energy content, thus e.g. ”

“ A. The initial state shall be that of rest; shall be the values of the relevant state variables. We change the volume adiabatically from to ; then the energy assumes the value .
B. We bring the body to the velocity . ”

“ The energy content of the cavity is:
where means the relative velocity:
If we set in the previous integral according to (19) :
then it becomes:
The second summand is equal to:
as one can most simply recognize by comparison with the penultimate equation of p. 11 of my first report. In consequence of (2) it is therefore:
The quantity is thus identical with the energy of the true radiation, which was indeed to be expected. If we introduce and by means of (20) and (21) , then
However, according to (16) it is:
where is the radiation intensity in the resting cavity. ”

“ Equation (7) shows that this condition is satisfied, when we put
is the integrating denominator of , when we (analogous to the preceding) understand under the temperature assumed by the body when it is adiabatically and isochorically brought to velocity zero. The arising function of plays here the role of a constant, so it is irrelevant. Of course, it must have the same value for all bodies.
Since we see as constant in this case, it is
In a system whose velocity isn't changing, plays the role of the inner energy for a co-moving observer ”

“ In order to calculate the absolute energy flow, i.e. the energy flow through a cross-section imagined as at rest, we have to add the product of the energy density multiplied with the translation velocity, to the relative energy flow in the direction of motion, i.e. ”

“ Compare for instance F. Hasenöhrl, Jahrb. d. Radioaktivität, 2, p. 281 (1905) . ↑ This terminology agrees with the one used in an earlier paper (Ann. d. Phys., 15 [1904] ) . There, and was written instead of and . ”