Setting potentials

I'm trying to set electrical potentials of conducting cylinders, using boundaries returned by mesh.GetBoundaries(). But this seems to return one less boundary than it should do. What am I doing wrong? Is there a better way to code this?

If everything were correct the cylinders shown by netgen would have uniform colours (yellow, red, blue).

Regards,
Andrew.

I worked out how to do this - eventually.
Working code attached.
Andrew.