Nevertheless if, as fast as more iron can be thus supplied, the ship-building industry goes on growing--if, consequently, the iron-makers experience a permanently-increased demand, and out of their greater profits get higher interest on capital, as well as pay higher wages; there will eventually be an abstraction of capital and labour from other industries to enlarge the iron-producing industry: new blast-furnaces, new rolling-mills, new cottages for workmen, will be erected. But obviously, the inertia of capital and labour to be overcome before the iron-producing industry can grow by a decrease of certain other industries, will prevent its growth from taking place until long after the increased ship-building industry has demanded it; and meanwhile, the growth of the ship-building industry must be limited by the deficiency of iron. A remoter restraint of the same nature meets us if we go a step further--a restraint which can be overcome only in a still longer time. For the manufacture of iron depends on the supply of coal. The production of coal being previously in equilibrium with the consumption; and the consumption of coal for the manufacture of iron being but a small part of the total consumption; it follows that a considerable extension of the iron manufacture, when it at length takes place, will cause but a comparatively small additional demand on the coal-owners and coal-miners--a demand which will not, for a long period, suffice to cause enlargement of the coal-trade, by drawing capital and labour from other investments and occupations. And until the permanent extra demand for coal has become great enough to draw from other investments and occupations sufficient capital and labour to sink new mines, the increasing production of iron must be restricted by the scarcity of coal, and the multiplication of ship-yards and ship-builders must be checked by the want of iron. Thus, in a community which has reached a state of moving equilibrium, though any one industry directly affected by an additional demand may rapidly undergo a small extra growth, yet a growth beyond this, requiring as it does the building-up of subservient industries, less directly and strongly affected, as well as the partial unbuilding of other industries, can take place only with comparative slowness. And a still further growth, requiring structural modifications of industries still more distantly affected, must take place still more slowly.