Living deep in our sea of air, we are no more aware of weight impinging upon us than a sea-dwelling fish under tons of water. Yet, at sea level, some 14 pounds of air press against every square inch of our bodies, equalized by internal counter pressure. Only as we move from low desert into the highlands do some facets of this pressure become evident, as when shortness of breath reminds us of thinning air.
In these modern days of sophisticated instrumentation, we tend to
forget the practical difficulties of the past—of even determining something as
seemingly simple as elevation. Early exploratory pushes into the Southwest by United
States forces took advantage of the decreasing weight of air as one ascends to
estimate, in a roundabout way, the distance above sea level. As people who cook at high
elevations soon learn, water boils at lower and lower temperatures as the air pressure
on its surface decreases. Simple conversion tables and a thermometer reveal a
camp's elevation by merely noting the temperature at which the coffee water
boils.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.