  A hydrodynamic mechanism of interactions of colloidal particles is
considered. The mechanism is based on the assumption of tiny background flows
in the experimental cells during measurements by Grier at al. [1-6]. Both
trivial (shear flow) and non-trivial (force propagation through viscous fluid)
effects are taken into account for two colloidal particles near a wall bounding
the solvent. Expressions for the radial (attractive or repulsive) forces and
the polar torques are obtained. Quantitative estimates of the flow needed to
produce the observed strength of attractive force are given, other necessary
conditions are also considered. The conclusion is made: the mechanism suggested
most likely is not responsible for the attractive interactions observed in the
experiments of Grier at al.; however, it may be applicable in other
experimental realizations and should be kept in mind while conducting colloidal
measurements of high sensitivity. Several distinctive features of the
interactions due to this mechanism are identified.
