At one time, it was thought that heat and cold were substances that could be combined in the proper proportions to make warmth and coolness. More recent discoveries indicate that a decrease in heat consists of a decrease in rate of molecular motion. When such a business becomes of age, however, it is more likely to take fewer chances, to be more sure of its investments and ventures. It is not in forgetting the happy past. People bring us well-meant but small consolation when they tell us what time will do to help our grief.
Air pressure is analogous to water pressure.
A submarine rising from the ocean bottom is subjected to decreasing pressure as it approaches the surface. Pythagoras, an ancient Greek, discovered the true nature of the harmonic series by observing the vibration of a single taut string stretched over a resonator. When a movable bridge was placed at the string's midpoint, the string vibrated in two segments at twice the speed at which it vibrated without a bridge. When moved to a third of the string's length, the string would vibrate in three segments at three times the speed. This phenomenon was repeated with each successive position of the bridge.