In 1896 Wien empirically determined a distribution law of blackbody radiation, later named after him: Wien's law. Max Planck, who was a colleague of Wien's, did not believe in empirical laws, so using electromagnetism and thermodynamics, he proposed a theoretical basis for Wien's law, which became the Wien–Planck law. However, Wien's law was only valid at high frequencies, and underestimated the radiancy at low frequencies. Planck corrected the theory and proposed what is now called Planck's law, which led to the development of quantum theory. However, Wien's other empirical formulation formula_1, called Wien's displacement law, is still very useful, as it relates the peak wavelength emitted by a body ("λ"max), to the temperature of the body (T). In 1900 (following the work of George Frederick Charles Searle), he assumed that the entire mass of matter is of electromagnetic origin and proposed the formula formula_2 for the relation between electromagnetic mass and electromagnetic energy.