On the other hand, again, when the consumption side of the wheel is stimulated for any reason, as from good harvests, easy credit, high wages, or business prosperity generally, the production side of the wheel is quickened to keep pace with it; so that everywhere production must keep time and pace with consumption, and consumption with production, as one side or aspect of a wheel keeps time and pace with the other. Had what is being consumed not been produced by human agency at all, but descended from the clouds like manna, and in unlimited quantity like air or water, it would of itself fall off the wheel of wealth, and form no part of the pure science of Political Economy. On the other hand, were it intercepted, 'cornered,' and monopolised, either by individuals or classes, so that it commanded a price, and to that extent slowed the movement of the wheel on the side of consumption, it would be a subject for politics and legislation to deal with, but would form no part of the pure science of Political Economy.

Again should the obstruction appear in the medium of the powers of Nature and of Man, in and through which this double-sided process of production and consumption functions, as for example when a particular kind of requisite human skill is not for the moment available, or when the world is waiting for some invention that shall yoke the powers of Nature to the aid of Man for the production of an article for which the market is practically unlimited, as for the cottons and woollens of England before the invention of the steam-engine, the spinning-jenny, the power-loom and the rest; in all such cases the obstruction caused by the deficiency of skill, or involved in the use of hand-labour instead of machinery, will act as a brake on the whole wheel, and will slow it in proportion to the degree or amount of that obstruction, precisely in the same way as a deficiency of motor power at any point where it is wanted, will slow at every point the movements of a mechanical wheel. The wheel of wealth, again, will also be slowed by all difficulties of transport at whatever points arising, as a carriage is by the roughness of the roads over which it runs.

The second point of identity between the wheel of wealth and a mechanical wheel is, that just as the distance covered by a running wheel in a given time is in proportion to the speed of its revolutions, so in the wheel of wealth-reproduction, the increase of wealth is also in proportion to the speed of its revolutions in a given time, or, in other words, to the quickness of the 'turnover,' as it is called; the number and rapidity of the sales of goods over the retail counters of the world determining the number and rapidity of the looms that are at work in producing them, of the soils that are cultivated, of the mines that are opened, of the ships that are launched, and of the railways and bridges that are built.

From all of which it would appear that the symbol of a revolving wheel is the natural symbol of the reproduction of wealth, and that the laws of the increase or decrease of wealth, as well as the immediate deductions therefrom, must be identical with, and so be transferable from the mathematics of a mechanical wheel to the wheel of wealth and the science of Political Economy. But it must not be forgotten that it is only with the pure science of Political Economy that we are here dealing, and that it is only in this pure science that the identity of the laws of a mechanical wheel and of the wheel of wealth holds good. For it is only in pure sciences, like the mathematical, that the symbols, the conditions, and the presuppositions are all assumed to be ideal to start with. In the case of the mechanical wheel, we assume that its sides or aspects are equal and evenly balanced, that it moves without friction in a homogeneous medium, and that the powers that act on it are unlimited, and available to any extent on demand.

And so, too, with the wheel of wealth; we assume that consumption and production are equal and opposite and self-balancing; that all the factors are unlimited, elastic, and free, so that when one is increased for any reason the rest may be relied on to keep pace with it; production to keep pace with consumption, through the powers of Nature and of human skill being always present and ready to be drawn on by discovery, invention, organization, machinery, and the rest; consumption to keep pace with production, by such distribution of wealth and purchasing power as shall permit of it; so that all alike, production, consumption, powers of Nature, powers of Man, organization, invention, machinery, and transport, shall keep time and step together.