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. Prosperity ends in a crisis. The era of optimism dies in the crisis, but in dying it gives birth to an era of pessimism. This new era is born, not an infant, but a giant; for an industrial boom has necessarily been a period of strong emotional excitement, and an excited man passes from one form of excitement to another more rapidly than he p