The Thermal Radiation Formula of Planck (1900)
  We review the derivation of Planck's Radiation Formula on the light of recent studies in its centenary. We discuss specially the issue of discreteness, Planck's opinion on his discovery, and the critical analysis on the contributions by Ehrenfest, Einstein, Lorentz, etc. We also address the views of T.S. Kuhn, which conflict with the conventional interpretation that discontinuty was already found by Planck. 
Luis J. Boya (Zaragoza University)