Isotropic values basic principles

In homogeneous isotropic fluids the distribution of molecules can be advantageously defined in terms of distribution functions, which are, at least in principle, measurable by scattering techniques (sec. 1.7.7). Generally, distribution functions describe probabilities of finding molecules at a certain position with respect to one or more other molecules, i.e. they are functions of distances (r) or positions (r). They cany information about the extent to which the local density differs from its value = N/V, averaged over the system, i.e. over the volume or, for an interface, over a thin layer in this interface. Some basic principles were introduced in secs. I.3.9d,e. Distribution functions of various orders can be distinguished ... 

---