You are right, except that it doesn't matter much, since the falloff is exponential (i.e., faster than polynomial). According to one source on the internet, the density is only 50% of sea level density at approx. 4-5 miles, so the lion's share of the mass is within 15 miles. At 03:05 PM 8/1/2006, Daniel Asimov wrote:

<< If I remember my physics correctly, air pressure is approx. 14.7#/sq in, which is the weight of the entire column of air 1 inch square sitting on the square inch.

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Not to be a nitpicker, but since "up" is not given by a parallel vector field, wouldn't the shape of this "air column" be more like a frustum of a 4-sided pyramid -- with a spherical "one-square-inch" top of radius R ~ Earth's radius, and a spherical base, of radius R+h (where h = maximum distance of relevant air from Earth) ?

--Dan