moving in all direction with the same absolute[1] velocity , and that the direction of the energy flux, the "beam", is determined by the construction in accordance with Huyghens' principle, even when it is about the emission of a moving body.[2] Furthermore we naturally presuppose the unrestricted validity of the thermodynamic laws.
Despite of the essentially different starting point, still some points of contact with the electromagnetic theory will be given, especially with the work of Abraham[3] which appeared when the present work was already finished in the main. This mostly concerns various purely geometrical considerations, although they are not always so simple of not being capable to give rise to misunderstandings. As far as I can see, there is complete agreement between Abraham and me.
The content of the present work is shortly as follows: In § 1, the geometric relations between absolute and relative beam velocity and direction are stated. They partially have been stated already by other authors (as mentioned), though they had to be completely compiled here.
§ 2 gives the definitions for the concepts "absolute radiation", "total" and "true relative radiation"; also these concepts were (partly with another meaning) already formed by Abraham.[4] Furthermore the theorem is derived, that the "true relative" radiation of a moving black body obeys Lambert's cosine theorem.
In § 3, the density of radiation in a moving cavity is calculated. It consists of two parts,
- ↑ Of course, absolute shall always be understood as "with respect to the fixed stars".
- ↑ It is of course not evident a priori as remarked by Abraham l. c. (Rem. 3) p. 251, though (as I believe) it is a very plausible assumption.
- ↑ M. Abraham, Ann. d. Phys. 14. p. 236. 1904. (l. c.)
- ↑ M. Abraham, l. c. p. 245.
