so long as the selling price of the output reaUzes such a differential gain over the expenses of production, is the putative increased rate of earnings realized ; and so soon as such a differential advantage ceases, the era of prosperity enters on its closing phase.
Such a differential advantage arises mainly from two causes: (1) The lines of industry which are remote, industrially speaking, from the point of initial disturbance, — from which, that is to say, the lines of industry first and chiefly affected by the rise draw supplies of one kind or another, — these remote lines of industry are less promptly and less acutely affected by the favorable disturbance of the price level ; this retardation of the disturbance affords the industries nearer the seat of disturbance a differential advantage, which grows less the farther 1 removed the given enterprise is from the point of ' initial disturbance.* (2) The chief and most secure differential advantage in the case is that due to