The Pressure of Radiation

Abstract

I QUITE agree with Mr. C. G. Darwin's opinion, expressed in NATURE of January 22, that Boltzmann's proof of the fourth-power law, taken as he gave it, or as it is usually given in the text-books, cannot be applied as it stands to each separate frequency, because the adiabatic expansion, employed in performing the cycle, will bring the Doppler effect into play, and cause a small change in the frequency, thus confusing the issue. But I think the reason of this is that the proofs usually given assume too much, and neglect an essential point, expressly emphasised by Carnot himself in the application of his principle to the case of a saturated vapour. According to my view, the application of Carnot's principle to a single frequency should run somewhat as follows.