Black-body radiation
Planck presents his new black-body radiation formula
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Original prompt & settings (JSON) ↗Planck's famous law first appeared as a short correction to another physicist's equation — its title promised 'an improvement on Wien's spectral equation.'
19 October 1900: an improvement on Wien
At the German Physical Society's Berlin meeting on 19 October 1900, Max Planck presented a new spectral formula under the title 'Über eine Verbesserung der Wien'schen Spektralgleichung.' It covered both the high-frequency region where Wien's law worked and the low-frequency region where new measurements showed it failed.
The same meeting included Ferdinand Kurlbaum's report on long-wavelength measurements made with Heinrich Rubens — and those results agreed with Planck's formula.
The measurement that forced it
Rubens and Kurlbaum's far-infrared work had shown Wien's law breaking down at long wavelengths. Rubens told Planck of the limiting behaviour before the meeting, prompting him to construct an expression compatible with both regimes.
Rubens reportedly checked the new expression against his measurements during the night and found agreement throughout.
No quantum here yet
Nothing quantum appeared in the October presentation. Planck offered an interpolation based on the entropy of a resonator; he did not introduce energy elements or ε=hν at this meeting.
The society received a compact formula matching the available black-body measurements across the observed spectrum, and Planck then began seeking a principled derivation, which he presented on 14 December.
Sources
Researched 23 Aug 2026 4 sources 3 audit passes
How this was checked
Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →
What the sources leave uncertain
- The meeting date is secure. Later reminiscences differ slightly over precisely when Rubens first checked the formula against all his measurements, so the safest claim is that the experimental agreement was reported at or immediately around the 19 October meeting.