away from the wall normalized by ${\rm Ca}V_{B1}$ as a function of $\kappa (\equiv (1+\varepsilon)^{-1})$. (It should be noticed that although $\kappa$ as well as $\varepsilon$ are measures of the distance between the wall and the bubble, hereafter $\kappa$ is also used to make some equations for the wide gap case ($\kappa\ll 1$) simple.) The measured velocity is found to be much higher than the analytical solution especially for the large $\kappa$. A possible inference drawn from this result is that there exists an additional ingredient to generate repulsive force for narrow bubble-wall gap, which is not covered by the theory of [@mag2003].

As the most crucial restriction involved in the mirror image technique, we can raise an assumption that the bubble-wall distance is much longer than the bubble radius. However, with regard to an inertia effect on the lateral velocity of a rigid sphere, [@tak2004] experimentally demonstrated that the mirror image approach has robust applicability in prediction beyond the wide-gap precondition. At this moment, we cannot conclude whether the discrepancy in the deformation-induced migration velocity comes from the erroneous prediction due to the miscalculation or the contradictory conditions in the boundary element computation and the experiment with the theoretical 