Einstein's explanation of Brownian motion, as the zig-zag motion of particles suspended in gas is known, was the first experimental evidence of the existence of molecules.
Though this may seem like an unnecessary complication, it was just what an explanation of planetary motion required (for, in the modern view, planets really do move nonuniformly).
Consider the usual elementary textbook "scientific explanation" of the motion of the balls in the above example following their collision.
The explanation of Brownian motion by Einstein in 1905, as the effect of statistical mechanical fluctuations, made them appear directly observable and open to exploitation.
The chemical world system is used to support Bacon's explanation of celestial motion in the face of contemporary astronomical problems (Rees 1975b, 161f).
This requirement of mutual contact between mover and moved holds for most cases of locomotion, hence the need for the complicated machinery in the explanation of projectile motion in Physics 8.10.
This explanation of natural motion is supposed to explain why certain parts of plants and animals (e.g. the stem, thighs, arms and trunk) are rounded rather than triangular or polygonal.
