Aerostatics: Structure of the Atmosphere

Abstract

As noted in I1 an ideal fluid is conceived of as composed of small elements or particles having mass and moving freely and without shearing stress, one relative to another. We must also assume the existence of a gravity field as a result of which the pressure at any point in the fluid is measured by the action of gravity on the particles lying between such point and the outer boundary of the fluid. Thus with the atmosphere surrounding the earth, the pressure at any point (measured as the force on unit area) is equal to the weight of a column of air of unit area base and extending from the given point to the upper limits of the atmosphere. From the absence of shear it also results that such pressure at any point will act equally in all directions, and thus the pressure on the surface of any body immersed in the fluid will be ⊥ to such surface at each point.