  We explore two different problems in string theory in which duality relates
an ordinary p-form in one theory to a self-dual (p+1)-form in another theory.
One problem involves comparing D4-branes to M5-branes, and the other involves
comparing the Ramond-Ramond forms in Type IIA and Type IIB superstring theory.
In each case, a subtle topological effect involving the p-form can be recovered
from a careful analysis of the quantum mechanics of the self-dual (p+1)-form.
