  In studies on Marangoni type motion of particles the surface tension is often
approximated as a linear function of temperature. For deformable particles in a
linear external temperature gradient far from the reference point this
approximation yields a negative surface tension which is physically
unrealistic. It is shown that H.Zhou and R.H.Davis J. Colloid Interface Sci.,
n.181,60,1996 presented calculation where the leading deformable drop moved
into a region of negative surface tension. With respect numerical studies the
restriction of the migration of two deformable drops is given in terms of the
drift time.
