Planck and unwilled quanta

Max Planck, a theoretical physics professor in Berlin, decided at the dawn of XIX century to explain how Kirchoff’s laws of emmision and absorbtion of electromagnetic radiation come from the second principle  of thermodynamics.
Travelling to India he discovered America.

In 1899 Planck [1] obtained an energy-density u distribution vs. wavelength (i.e. frequency v) in a quite good agreement with the existing experimental data.
planck

Just when Planck announced with triumph his results, malicious voices in Berlin started to whisper, that new experimental data, in far infrared (at 50 micron), are not in accord with his “law”. At first October Sunday of  1900 the experimentalis H. Rubens (and others cited [2]) send to Planck their final results. Planck spent hectic two month trying  to fit with an analytical formula those data.

14 December 1900 on German Physics Society meeting  he showed a new formula, for which the previous one was only an approximation
planck


To obtain this formula Planck had to assume that the energy appears in “parts” proportional to the light frequency v: E=hv with constant h=6.55•10-34 Js .

Planck did not use the term “quant”, althrough he knew this word, what is clear from his article [3], just next page after the work [2]. Even in 1913 on the “Solvay” Congress he continued to insist that "photon" is a wrong hipothesis.

[1] Ueber irreversible Strahlungsvorgänge, Annalen der Physik IV, 1 (1900) 69
[2] Ueber das Gesetz der Energieverteilung im Normalspektrum, Ann. der Physik IV, 4 (1900) 553
[3] Ueber die Elementarquanta der Materia und Elektricitat, Ann. der Physik IV, 4 (1901) 564