Hero's engine was used only as a toy and it seems to represent all the ancients knew about the power of steam and all they did with it. It is not strange that they did not know more for there is no general rule by which discoveries are made. Sometimes even enlightened peoples have for centuries remained blind to the simplest principles of nature. The Greeks and Romans with all their culture and wisdom were ignorant of some of the plainest facts of science. It is a little strange, however, that after Hero's discovery was made known, men did not profit by it. It would seem that eager and persistent attempts would have been made at once to have steam do useful work, as well as furnish amusement. But such was not the case. Hero's countrymen paid but little attention to his invention and the steam-engine passed almost completely out of men's minds and did not again attract attention for nearly seventeen hundred years. About the end of the fifteenth century Europe began to awaken from a long slumber and by the end of the sixteenth century its eyes were wide open. Everywhere men were now trying to learn all they could. The study of steam was taken up in earnest about the middle of the sixteenth century and by the middle of the next century quite a little had been learned of its nature and power. In 1629 an Italian, Branca by name, described in a book a steam-engine which would furnish power for pounding drugs in a mortar. There was no more need for such a machine then than there is now and of course the inventor aroused no interest in his engine. You can easily understand how Branca's engine (Fig. 3) works. The steam causes the wheels and the cylinder to revolve. As the cylinder revolves, a cleat on it catches a cleat on the pestle and lifts the pestle a short distance and then lets it fall. Here the pestle instead of being raised by a human hand is raised by the force of steam. This engine would be more interesting if an engine had actually been made, but there is no reason to believe that Branca ever made the engine he described. We owe much to him, nevertheless, for suggesting how steam might be put to doing useful work. [Illustration: FIG. 3.--BRANCA'S ENGINE, 1629.] It was not very long before an Englishman put into practice what the Italian had only suggested. Edward Somerset, the Second Marquis of Worcester, in 1663 built a steam-engine that raised to the height of forty feet four large buckets of water in four minutes of time. This was the first useful work ever done by steam. Figure 4 shows the construction of Worcester's engine. [Illustration: FIG. 4.--WORCESTER'S ENGINE, 1663.] In this engine there was one improvement over former engines which was of the greatest importance: there was one vessel in which the steam was generated and another in which the steam did its work. The steam-engine now consisted of two great divisions, the boiler and the engine proper.