Do bubbles in Guinness go down?

Video clip 3

Clip 1 What can I see in this clip?

This clip is a zoomed-in shot (about x6 magnification) taken at the top of the glass just below the head.  Being further up, and slightly later in the settling process, you can see that the bubbles are moving much more slowly than in the other clips.  You can also see that there are some bubbles going down, and many going up (just in case you thought the clips were trick shots!).  The bubbles are going up faster in the background.  Also, the bubbles that are going down in the foreground are smaller: the larger bubbles in the foreground are hardly moving.  These observations are all consistent with the fact that the pint has nearly settled: the number of waves of liquid has decreased.  Also, because we are nearer the top of the glass, we are near to the point where the waves turn over and start to go down, so they are slower.  Incidentally, the bubbles are more clearly seen in this shot because it was easier to light the shot from below.
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(c) 2004 Alexander & Zare