to their natural vibration, but they are not capable of changing their frequencies, so long as they exert or suffer no other action than emitting or absorbing radiant energy.Compare P. Ehrenfest, Wien. Ber. 114 [2a], p. 1301, 1905. Ann. d. Phys. 36, p. 91, 1911. H. A. Lorentz, Phys. Zeitschr. 11, p. 1244, 1910. H. Poincaré, Journ. de Phys. (5) 2, p. 5, p. 347, 1912.
To get an insight into those processes by which the exchange of energy between rays of different frequencies takes place in nature would require also an investigation of the influence which the motion of the oscillators and of the electrons flying back and forth between them exerts on the radiation phenomena. For, if the oscillators and electrons are in motion, there will be impacts between them, and, at every impact, actions must come into play which influence the energy of vibration of the oscillators in a quite different and much more radical way than the simple emission and absorption of radiant energy. It is true that the final result of all such impact actions may be anticipated by the aid of the probability considerations discussed in the third section, but to show in detail how and in what time intervals this result is arrived at will be the problem of a future theory. It is certain that, from such a theory, further information may be expected as to the nature of the oscillators which really exist in nature, for the very reason that it must give a closer explanation of the physical significance of the universal elementary quantity of action, a significance which is certainly not second in importance to that of the elementary quantity of electricity.
List of the papers published by the author on heat radiation and the hypothesis of quanta, with references to the sections of this book where the same subject is treated.
german Absorption und Emission elektrischer Wellen durch Resonanz. Sitzungsber. d. k. preuss. Akad. d. Wissensch. vom 21. März 1895, p. 289–301. Wied. Ann. 57, p. 1–14, 1896.
Ueber elektrische Schwingungen, welche durch Resonanz erregt und durch Strahlung gedämpft werden. Sitzungsber. d. k. preuss. Akad. d. Wissensch. vom 20. Februar 1896, p. 151–170. Wied. Ann. 60, p. 577–599, 1897.
Ueber irreversible Strahlungsvorgänge. (Erste Mitteilung.) Sitzungsber. d. k. preuss. Akad. d. Wissensch. vom 4. Februar 1897, p. 57–68.
Ueber irreversible Strahlungsvorgänge. (Zweite Mitteilung.) Sitzungsber. d. k. preuss. Akad. d. Wissensch. vom 8. Juli 1897, p. 715–717.
Ueber irreversible Strahlungsvorgänge. (Dritte Mitteilung.) Sitzungsber. d. k. preuss. Akad. d. Wissensch. vom 16. Dezember 1897, p. 1122–1145.
Ueber irreversible Strahlungsvorgänge. (Vierte Mitteilung.) Sitzungsber. d. k. preuss. Akad. d. Wissensch. vom 7. Juli 1898, p. 449–476.
Ueber irreversible Strahlungsvorgänge. (Fünfte Mitteilung.) Sitzungsber. d. k. preuss. Akad. d. Wissensch. vom 18. Mai 1899, p. 440–480. (§§ 144 bis 190. § 164.)
Ueber irreversible Strahlungsvorgänge. Ann. d. Phys. 1, p. 69–122, 1900. (§§ 144–190. § 164.)
Entropie und Temperatur strahlender Wärme. Ann. d. Phys. 1, p. 719 bis 737, 1900. (§ 101. § 166.)