  We present accurate measurements of the relative motion and deformation of
two large bubbles released consecutively in a quiescent liquid confined in a
thin-gap cell. Though the second bubble injected is smaller, we observed that
in all cases it accelerates and catches up with the leading bubble. This
acceleration is related to the wake of the leading bubble which also induces
significant changes in the width and curvature of the trailing bubble. On the
contrary, the velocity of the leading bubble is unaltered during the whole
interaction and coalescence process. Shape adaptation of the two bubbles is
observed just prior to coalescence. After pinch-off, the liquid film is drained
at a constant velocity.
