Balance  of Force in the Vertical: Hydrostatic Balance
					Vertical pressure force =  Gravitational force               - (dP) x (dA) = r x (dz) x (dA) x g                               dP =  -rgdz Since P= rRT,                               dP =  -P/RT x gdz                            dP/P =  -g/RT x dz                                 P =  Ps exp(-gz/RT)