This condition of natural balance between production and consumption was profoundly disturbed by the introduction of the steam engine; but even so there were still some limits, though of a quite different kind, to local concentrations of productive power. For steam engines require water and coal at the scene of action, and these take up space and need continual shifting and replenishing. Owing to the very nature of physical matter, it cannot be heaped up where it is required in unlimited quantities.