The term ''atmosphere'' has sometimes been used by [[Chemistry|Chemists]] and [[Physics|Physicists]] as a unit of [[pressure]]. Example: one atmosphere of pressure is the pressure exerted on objects by the atmospheric [[gas]]ses, [[air]] (principally 21% [[oxygen]] and 79% [[nitrogen]]), at sea level of approximately 14.7 pounds per inch square. | The term ''atmosphere'' has sometimes been used by [[Chemistry|Chemists]] and [[Physics|Physicists]] as a unit of [[pressure]]. Example: one atmosphere of pressure is the pressure exerted on objects by the atmospheric [[gas]]ses, [[air]] (principally 21% [[oxygen]] and 79% [[nitrogen]]), at sea level of approximately 14.7 pounds per inch square. |