Using a heuristic of quantization, which he gleaned from Boltzmann, Planck argued that a resonator tuned to frequency ν ν , with average energy E , would contain entropy S ν ν = k B [ ( 1 + E h ν ν ) ln ⁡ ⁡ ( 1 + E h ν ν ) − − E h ν ν ln ⁡ ⁡ E h ν ν ] for some constant h (later termed the Planck constant). Then applying k B T = ( ∂ ∂ E S ) − − 1 , Planck obtained the black body radiation law.