  This note considers how hydrodynamic interactions between a pair of rods slow
the motion of each rod. Rods are approximated as being nearly straight lines of
pointlike beads. Hydrodynamic interactions between the beads are treated with
generalizations, developed by Kynch (J. Fluid Mech. 5, 193-208 (1959)) and by
Mazur and van Saarloos (Physica A 115, 21-57 (1982)) of the Oseen and
Rotne-Prager hydrodynamic interaction tensors. We find that the hydrodynamic
interactions between two rods, as they affect the mobility of a given rod, are
with a minor exception not very different from the interactions between two
beads, especially when the two rods are even modestly separated. At the level
of approximation of bead-spring models of polymer coils, it therefore does not
appear to be advantageous to replace sphere-sphere hydrodynamic interaction
tensors with more elaborate rod-rod hydrodynamic interaction tensors.
