Of the various applications of steam, and other industrial inventions, I would say, as of the art of printing, that they are great means, but their results depend upon the agent. Such arts might be practised by rote long after the intellectual activity that produced them had ceased. There are innumerable instances of processes which continue in use, though the theoretical secret is lost. It is therefore not unreasonable to suppose, that the practice of our inventions might survive our civilization; that is, it might continue when these inventions were no longer possible, when no further improvements were to be hoped for. Material well-being is but an external appendage of a civilization; intellectual activity, and a consequent progress, are its life. A state of intellectual torpor, therefore, cannot be a state of civilization, even though the people thus stagnating, have the means of transporting themselves rapidly from place to place, or of adorning themselves and their dwellings. This would only prove that they were the _heirs_ of a former civilization, but not that they actually possessed one. I have said, in another place, that a civilization may thus preserve, for a time, every appearance of life: the effect may continue after the cause has ceased. But, as a continuous change seems to be the order of nature in all things material and immaterial, a downward tendency is soon manifest. I have before compared a civilization to the human body. While alive, it undergoes a perpetual modification: every hour has wrought a change; when dead, it preserves, for a time, the appearance of life, perhaps even its beauty; but gradually, symptoms of decay become manifest, and every stage of dissolution is more precipitate than the one before, as a stone thrown up in the air, poises itself there for an inappreciable fraction of time, then falls with continually increasing velocity, more and more swiftly as it approaches the ground. Every civilization has produced in those who enjoyed its fruits, a firm conviction of its stability, its perpetuity.