Abstract.
Stellar dynamics occupied Chandrasekhar.s interest for a brief
interlude
between his more prolonged studies of stellar structure and radiative
transfer. This
paper traces the history of one of his ideas . namely, that the shape of
the galactic
potential controls the orientation of the stellar velocity dispersion
tensor. It has its
roots in papers by Eddington (1915) and Chandrasekhar (1939), and
provoked a fascinating
dispute between these two great scientists . less well-known than their
famous
controversy over the white dwarf stars. In modern language, Eddington
claimed that
the integral curves of the eigenvectors of the velocity dispersion
tensor provide a onedimensional
foliation into mutually orthogonal surfaces. Chandrasekhar challenged
this, and explicitly constructed a counter-example. In fact, the work of
neither of these
great scientists was without flaws, though further developments in
stellar dynamics
were to ultimately draw more on Eddington.s insight than
Chandrasekhar.s. We conclude
with a description of modern attempts to measure the orientation of the
velocity
dispersion tensor for populations in the Milky Way Galaxy, a subject
that is coming
into its own with the dawning of the age of precision astrometry.
Keywords : celestial mechanics - stellar dynamics - galaxies: kinematics
and dynamics