The Atmosphere is Massive

What is air Paraphrasing David Abramh We are immersed in the invisible air, but we barely even perceive it. We sense its effects—it is needed to support life— 

Why learn the gas laws in chemistry We have known since the early nineteenth century that the gaseous state is where molecules roam as freely as individuals. This permits understanding of their physical and chemical behavior at the simplest levels. We also learned that two equal-sized balloons of hydrogen gas react totally and precisely with one equal-sized balloon of oxygen gas to produce water identical in mass to the two gases combined. 

FIGURE 143. A figure from Blaise Pascal s Traitez de I Equilibre des Liqueurs, et de La Pesanteur de La Masse de L Air (Paris, 1663) depicting a highly stylized barometer. He sent his brother-in-law Perier to measure the atmospheric pressure on a mountain top (courtesy Edgar Fahs Smith Collection, Rare Book and Manuscript Library, University of Pennsylvania). 

FIGURE 145. The Boylean vacuum pump, built by Robert Boyle s assistant Robert Hooke (from New Experiments Physico Mechanical, Touching The Spring of the Air, 2nd ed., London, 1662). 

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