A spherical gravitational source has an external gravitational field that falls off precisely as the inverse square of the distance from the sphere's center. (scientificamerican.com)
This is certain, that it must proceed from a cause that penetrates to the very centres of the sun and planets, without suffering the least diminution of its force; that operates not according to the quantity of the surfaces of the particles upon which it acts (as mechanical causes use to do), but according to the quantity of the solid matter which they contain, and propagates its virtue on all sides to immense distances, decreasing always as the inverse square of the distances.... (religion-online.org)
«If we find objects whose brightness changes with the inverse square of distance, we won't say, «Oh, no! (discovermagazine.com)