A fluid is considered homogenous from the standpoint of mass if its density is uniform throughout. Such an idealized state is rarely if ever attained except for limited portions of a fluid, since all real fluids are to some extent compressible and consequently their density must vary in the direction of gravity. The sea relative to the atmosphere might be considered as homogeneous. However, it will be shown later that even the slight variations in density which do exist are of prime importance in the computation of ocean currents.
In an idealized homogeneous fluid the isobaric surfaces
under quasi-static conditions would all have the same
inclination relative to the surfaces of 
and
would have a spacing (for equal units of p) which
would be proportional to g alone. Since the latter
varies only slightly with elevation, the geometrical
spacing would consequently be very nearly constant.
The spacing of the surfaces of p with respect
to would be exactly constant. This situation is
schematically illustrated in Fig. 3.08-1(a).