• The gravitation constant is the same always. But the economic constants-these elasticities of demand and supply-depending, as they do, upon human consciousness, are liable to vary. The constitution of the atom, as it were, and not merely its position, changes under the influence of environment.

    "The Economics of Welfare". Book by Arthur Cecil Pigou (4th edition, 1932), Ch. 1 : Welfare and Economic Welfare, § 4, 1920.