I was reading Quantum chemistry by McQuarrie and in it he states that according to classic electromagnetic theory (prior to quantum mechanics) intensity of radiation is given by the Rayleigh- Jeans law (which was inaccurate as it showed the ultraviolet catastrophe). In the Rayleigh- Jeans law EM intensity is proportional to frequency squared and the black body temperature.
However in describing the failure of classic EM to deal with the photoelectric effect the book states that the, "the intensity of the radiation is proportional to the square of the amplitude of the electric field." (for classic EM) and the intensity shouldn't depend on frequency (it was Einstein who introduced the frequency dependence of intensity)
So I'm confused - the Rayleigh- Jeans law is a classical law for intensity of EM radiation and depends on freqency, but the book says that according to classical theory the intensity depended on amplitude of the E field and not frequency.
Isn't this a contradiction?