(4) Lastly, much later, come products of an already mature civilization, artificial motors, explosives,--powder and all its derivatives and substitutes--steam, which has made such great progress. If the reader please to represent to himself well the immense number of facts that we have just indicated in a few lines; if he please to note that every invention, great or small, before becoming a fixed and realized thing, was at first an imagination, a mere contrivance of the brain, an assembly of new combinations or new relations, he will be forced to admit that nowhere--not excepting even esthetic production--has man imagined to such a great extent. One of the reasons--though not the only one--that supports the contrary opinion is, that by the very law of their growing complexity, inventions are grafted one on another. In all the useful arts improvements have been so slow, and so gradually wrought, that each one of them passed unperceived, without leaving its author the credit for its discovery. The immense majority of inventions are anonymous--some great names alone survive. But, whether individual or collective, imagination remains imagination. In order that the plow, at first a simple piece of wood hardened by the fire and pushed along with the human hand, should become what it is to-day, through a long series of modifications described in the special works, who knows how many imaginations have labored! In the same way, the uncertain flame of a resinous branch guiding vaguely in the night leads us, through a long series of inventions, to gas and electric lighting. All objects, even the most ordinary and most common that now serve us in our everyday-life, are _condensed imagination_.