It is shown in the article Astronomy (Celestial Mechanics) that the mean distance and mean motion or time of revolution of a planet are so related by Kepler's third law that, when one of these elements is given, the other can be found.
Taking the mean distance of this group as that of a planet, the distance of the major planets closely approximates to Bode's law, except in the case of Neptune.
Its mean distance from the sun is 1.46 times i that of the earth; but, besides, the eccentricity of its orbit is large (0.22), so that at the most favourable opportunity it can come within one-seventh of the distance of the sun.
If so, it is clear that their mean distance apart, averaged through a sufficiently long interval of their motion, will be greater than a.
If we suppose that upon the whole the air cannot be removed, so that the mean distance between the opposed surfaces remains constant, the electric attractions tend to produce an instability whereby the smaller intervals are diminished while the larger are increased.
In their withdrawal, by a historic disregard of fair play, the Germans not merely refused to put at the disposal of the Lithuanian authorities the necessary means of defence, but under a military convention allowed the Bolshevist troops to march into evacuated zones at a mean distance of io kilometres.
When the molecules are oscillating about their equilibrium positions, there is no reason why their mean distance apart should be the same as when they are at rest.