of a sphere with the same volume. Introducing an interfacial deflection $f(\theta,\phi)$ from a sphere, we write the distance from the bubble centroid to the interface as $a+f$. The experimental results used here were measured under the condition that the Reynolds number ${\rm Re}=2\rho aV_{B1}/\mu$ (here $V_{B1}(={\bm V}_B\cdot{\bm e}_{1}$), $\rho$, and $\mu$ respectively denote the rising velocity, the density, and the dynamic viscosity of liquid) is unity or less ([@tak2002]). The pure lateral migration velocities induced by the deformation $V_{B3}$ were calculated from the measured values substituting the velocities induced by the inertia effects. Following a Stokes flow theory for the deformation-induced migration ([@mag2003]), we can characterize the system using two parameters, i.e., a clearance parameter $\varepsilon(= c/a)$ and a capillary number ${\rm Ca}=\mu V_{B1}/\gamma$ (or a Bond number ${\rm Bo}=\rho a^2 g/\gamma$ as used in [@mag2003]). Here $\gamma$ and $g$ respectively denote the surface tension and the acceleration of gravity. Further, as long as ${\rm Ca}\ll 1$, we may use ${\rm Ca}$ as a perturbation parameter, and reduce the ${\rm Ca}$-dependent system to another, in which $V_{B1}$, $V_{B3}/{\rm Ca}$ and $f/{\rm Ca}$ are dependent only upon $\varepsilon$, under the infinitesimal deformation assumption. Figure \[fig:migvel\_comp\_exp\] shows the migration velocity $V_{B3}$ 