1.   The mean density of Mercury indicates that its interior is substantially different from the interiors of the other terrestrial planets.

2.   Although the atomic beam pulses spread out during a particular measurement, owing to velocity dispersion, calculations show that the mean density quoted here is the important measure.

3.   Oceanic lithosphere has a mean density rather close to that of the immediately underlying asthenosphere.

4.   By contrast continental lithosphere has a significantly lower mean density than oceanic lithosphere and its buoyancy with respect to the asthenosphere prevents all but limited subduction.

5.   We are concerned with the predominantly horizontal mean flow of a fluid whose mean density varies vertically.