Planck also worked to devise a classical thermodynamic theory for blackbody radiation, like Rayleigh and Jeans. His basic concepts and approach were identical to their's, up to a very significant point. You see, Planck recognized that the Rayleigh-Jeans idea had a severe, classical flaw in it. Using their method, the energy associated with Maxwell's electromagnetic fields is infinite!

Planck's idea was a trick used by physicists to this day to take care of unwanted "infinities" in some theories; he took the continuity of possible classical energies for the light (electromagnetic fields) and divided it into discrete increments. Then, later on, he would make the increment size decrease to zero.

In his case, the energy increments depend on a fundamental size related to the frequency of the electromagnetic field making up the light; E_packet=hn, where n is the frequency of the light. There were still an infinite number of these increments, but the act of dividing them up amazingly changes the mathematics that describes them. Now, the infinite field energy becomes quite finite and was in remarkable agreement with experiment. Indeed, the best agreement between experiment and Planck's theory came when the increment size had a particular value that is now known as Planck's constant, h@6.627x10^-34 Joule-s.

The only trouble that Planck had was when he went to take the next mathematical step of "letting the increment size decrease to zero." No matter how carefully he did it, he always got the Rayleigh-Jeans answer back again. You see, Planck did not really believe that the energy of the electromagnetic fields came in discrete sizes. Planck had come to the same point in his theory that Einstein would soon arrive at concerning the photoelectric effect, but Einstein - unlike Planck - decided that it was an acceptable answer.