Russell
In all this universe, like conditions seek like conditions. Gases and vapors seek gases and vapors by rising to find them. Liquids and solids seek liquids and solids by falling toward them. [A New Concept of the Universe, page 18]
Radiating matter seeks a radiating condition in the outward direction of radiation. Gravitating matter seeks the inward radial direction of condensation to find its like condition. [A New Concept of the Universe, page 18]