  In three dimensions, an abelian gauge field is related by duality to a free,
periodic scalar field. Though usually considered on Euclidean space, this
duality can be extended to a general three-manifold M, in which case
topological features of M become important. Here I comment upon several of
these features as related to the partition function on M. In a companion
article, arXiv:1405.2483, I discuss similarly the algebra of operators on a
surface of genus g.
