All About Engines

26 All About Engines from the top of the leaning tower of Pisa, and found that they touched the ground at the same instant. And by these and other experiments he laid the foundation of the modern science of mechanics. Again, Torricelli, a pupil of Galileo, invented the barometer, explained atmospheric pressure and the action of the common pump, and made clear the meaning of the ancient saying that “ Nature abhors a vacuum.” It followed from Torricelli’s experi- ments that the atmosphere which surrounds the earth presses upon its surface with a force of 147 lb. per square inch at the sea level. This pressure is greater at the bottom of a well or a mine, and less as we ascend a mountain. Since the body of a man has an area of about 15 square feet, the pressure he supports under ordinary conditions is nearly 15 tons ! In these times of intense curiosity and feverish inquiry lived one Branca, who pursued his studies in the University of Padua. He constructed an engine in 1619 which is illustrated in Fig. 13, Plate 2. In this case the boiler did not rotate itself, but was used merely to supply steam. The revolving portion consisted of a wheel formed of two discs, with divisions between which acted as vanes. The steam formed in the boiler issued from a tube and, impinging upon the vanes, caused the wheel to spin round. In the illus- tration it is shown working a mortar for grinding materials to powder. Nearly three hundred years later, when tools and materials had endowed in- ventors with new and more wondrous powers, Dr.