It was believed until the turn of the century that the spectrum of electromagnetic waves (heat, light, micro- and radio-waves) was 'continuous'. Since all these waves convey energy, it was believed that energy is also continuous and infinitely divisible.
-- Nevertheless, in studying 'black-body' radiation it was discovered that this is not true. The predictions of classical physics about the energy distribution among the various frequencies were ambiguous. The experimental curve could not be reproduced from any classical laws or equations. Wien's curve was a good approximation for the higher frequencies but it was off for the lower ones, Raleigh's curve was close to the lower ones but predicted an unreal 'ultaviolet catastrophe'.
Faced with this conceptual dead-end, Max Planck experimented with the mathematical interpolation of the two wrong equations hoping to derive a new one that reproduced the experimental curve. However, this mathematical sculpturing showed that the experimental curve could not be exactly matched by any formula, without giving up the basic idea that energy is continuous. Planck finally concluded that energy comes in infinitesimally small, minimal 'quantities'. -- Calculating backward from the experimental curve, Planck arrived to a 'constant' of a given, very minute number that, when inserted into the equation indeed reproduced the initial experimental curve. -- Planck gave the symbol 'h' to this number and called it the fundamental 'Quantum of energy'.
Based on the ideal gas model of the Aether, AETHRO-KINEMATICS renders a conceptual explanation why Planck's mathematical sculpturing works, and why the discontinuity of energy, or 'Quantum', became one of the fundamental theories of physics.