The earth’s atmosphere is a thin layer of gases around the planet. This thin layer of gases is commonly called, air. It is retained by the earth’s gravity. It extends from a few meters below the surface of the earth to a height of about 60,000 kms. Most of the atmospheric mass is located near the surface, up to a height of 80 to 100 kms. As a result, the air exerts pressure vertically below it. The highest pressure is felt near the surface of the earth and the pressure decreases with increasing altitude. On average, 1013 mb of pressure is observed at the earth’s surface. The density of air at the Earth’s surface is about 1.2 kg/m3 (Padmanabha Murty, 2004). The density too decreases with increasing height.