"The spread of Christianity throughout Europe caused the foundation of many religious communities, and the severe rules by which they were governed—fixing the hours of prayer, labor, and refreshment—forced their members to seek instruments by which to measure time. In the year 605, a bull of Pope Sabinianus decreed that all bells be rung seven times in the twenty-four hours, at fixed moments and regularly, and these fixed times became known as the seven canonical hours. The sound of the bells penetrated and came to regulate not only the life of the religious bodies but also that of the secular people who lived outside the walls of the monasteries. Oil-lamps, candles, hour-glasses, prayers and—for those who had the means of buying them—clepsydræ served as chronometers for the brotherhoods; so that one can easily imagine that many a monk sought to improve these instruments. But as yet, no one had found means to regulate the wheel-system of a movement. In the best instruments of this period, water supplied the motive power and served as well to regulate the action." There is a general belief that Gerbert, the monk, who was the most accomplished scholar of his age, and who later became Pope Sylvester II, was the one who first took the important step of producing a real clock, and that this occurred near the close of the tenth century—or to be more exact, about 990 A. D. This period was one of densest superstition, and expectancy of the end of the world was in the air, since many people had fixed upon the year 1000 A. D. as the date of that cataclysmic event. Authorities of the Church and of the state were not very partial to invention and research, their attention being fixed largely upon theological, political, or military affairs; but, of course, inquiring and constructive minds were still to be found; even without encouragement these tended to follow the impulse of their natures. [Illustration: GALILEO DISCOVERING THE PRINCIPLE OF THE PENDULUM _As a youth of seventeen Galileo watched a swinging lamp, in the Cathedral of Pisa, timed it by his pulse, and discovered the principle upon which pendulum clocks are built._] It is to the monks in their cloisters that we chiefly owe the preservation of learning through the "dark ages," and from the monks, for the most part, came such progress of science and invention as was made. If Gerbert, the monk, after patient tinkering with wheels and weights in his stone-walled workshop, really achieved some form of the clock-action as we know it, he was one of the great benefactors of the human race. Still, it is not impossible that his device may only have been a more remarkable application of the clepsydra principle.