9. Application to cavity radiation.
We base our calculation on the relative ray path. We consider radiation that encloses angles between and with the direction of motion; it carries – in unit volume through the unit surface of a perpendicular (co-moving) plane – the energy amount:
We call the intensity of the total (relative) radiation. If this radiation is incident upon an absorbing surface, it performs the pressure work:
where is the angle between the absolute radiation direction and the direction of motion. The difference:
we call the true (relative) radiation. The true radiation intensity
is crucial for the heat transport between bodies of equal velocity.
We employ the standpoint of Lorentz's contraction hypothesis and introduce the angle by the equation
- M. Abraham, Boltzmann-Festschrift, p. 90, 1904. 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 ). There, and was written instead of and . See also Jahrb. d. Radioaktivität und Elektronik, 2, p. 283 (1905).