Throughout the ages, man’s image of his environment has always been tempered by the existence of an inexhaustible frontier somewhere beyond the known world, an illimitable plane in which respite could be found once one’s immediate surroundings deteriorated socially or environmentally. More recently, man has had to become accustomed to the notion of a finite earth and a closed sphere of human activity. However, it was not until World War II and the air age that the global nature of our lives really entered the popular imagination, and in the intervening period we have not entirely come to terms with this transition from the illimitable plane to the closed sphere. Economists in particular have failed to come to grips with the ultimate consequences of this transition.