  We derive from first principles equations governing (a) the quadrupole tensor
of a star distorted by both rotation and the presence of a companion in a
possibly eccentric orbit, (b) a functional form for the dissipative force of
tidal friction, based on the concept that the rate of energy loss from a
time-dependent tide should be a positive-definite function of the rate of
change of the quadrupole tensor as seen in the frame which rotates with the
star, and (c) the equations governing the rates of change of the magnitude and
direction of the stellar rotation, and the orbital period and eccentricity,
based on the concept of the Laplace-Runge-Lenz vector. Our analysis leads
relatively simply to a closed set of equations, valid for arbitrary inclination
of the stellar spin to the orbit. The results are equivalent to classical
results based on the rather less clear principle that the tidal bulge lags
behind the line of centres by some time determined by the rate of dissipation;
our analysis gives the effective lag time as a function of the dissipation rate
and the quadrupole moment.
  We discuss briefly some possible applications of the formulation.
