behavior fig3 shows these three merge gap directions for a downward orientation of the 211 axis consistent with the arrangement of propagation loops shown in fig1 imaginary discs 21 22 23 and 24 are separated by gaps 26 27 and 28 which are oriented at 120 degrees to each other the arrows indicate the directions in which bubbles pass freely through gaps this figure can be used as a reference for fig4 6 to determine the behavior of a bubble at a gap as an example of bubble motion with respect to gaps in this type of configuration consider a bubble at point x of disc 21 if the drive field rotates counterclockwise the bubble moves counterclockwise along the periphery of disc 21 and approaches gap 26 as indicated by the arrow it passes through the gap thus in a field rotating counterclockwise a bubble originating at point x simply propagates continually around disc 21 consider however a bubble at point x in a clockwise rotating field this bubble approaches gap 26 from the right but rather than passing through it proceeds as if the gap were a cusp and transfers to disc 24 the bubble next encounters gap 27 we see that it passes through this gap and then propagates clockwise around disc 24 suppose however that when.