From the time of Hero until the seventeenth century there is no record of any attempt being made to utilize steam-pressure for a practical purpose. The fact seems strange only because steam-power is so prominent a fact with ourselves. The ages that intervened were, as a whole, times of the densest superstition. The human mind was active, but it was entirely occupied with miracle and semi-miracle; in astrology, magic and alchemy; in trying to find the key to the supernatural. Every thinker, every educated man, every man who knew more than the rest, was bent upon finding this key for himself, so that he might use it for his own advantage. During all those ages there was no idea of the natural sciences. The key they lacked, and never found, that would have opened all, is the fact that in the realm of science and experiment there is no supernatural, and only eternal law; that cause produces its effect invariably. Even Kepler, the discoverer of the three great laws that stand as the foundation of the Copernican system of the universe, was in his investigations under the influence of astrological and cabalistic superstitions. [Footnote: Kepler, a German, lived between 1571 and 1630. His life was full of vicissitudes, in the midst of which he performed an astonishing Even the science of amount of intellectual labor, with lasting results. He was the personal friend of Galileo and Tycho Brahe, and his life may be said to have been spent in finding the abstract intelligible reason for the actual disposition of the solar system, in which physical cause should take the place of arbitrary hypothesis. He did this.] medicine was, during those ages, a magical art, and the idea of cure by medicine, that drugs actually _cure_, is existent to this day as a remnant of the Middle Ages. A man's death-offense might be that he knew more than he could make others understand about the then secrets of nature. Yet he himself might believe more or less in magic. No one was untouched; all intellect was more or less enslaved. And when experiments at last began to be made in the mechanisms by which steam might be utilized they were such as boys now make for amusement; such as throwing a steam-jet against the vanes of a paddle-wheel. Such was Branca's engine, made nine years after the landing of our forefathers at Plymouth, and thought worthy of a description and record. The next attempt was much more practical, but cannot be accurately assigned. It consisted of two chambers, from each of which alternately water was forced by steam, and which were filled again by cooling off and the forming of a vacuum where the steam had been. One chamber worked while the other cooled. It was an immense advance in the direction of utility.