is the total energy of the system, and it will be seen that the equivalence of (8) and (11) follows immediately from (12).
In these deductions we have made no assumptions about the degree of eccentricity of the orbits. If the orbits are circular (11) is equivalent to the simple condition that the angular momentum of the system in the stationary states is equal to an entire multiple of
[9].
In Planck’s vibrators the particles are held by quasi-elastic forces, and the mean value of the kinetic energy is equal to the mean value of the potential energy due to the displacements. Consequently (11) forms a complete analogy to Planck’s original relation
between the energy
of a monochromatic vibrator and its frequency
