  The phase transition between the intermediate and normal states in type-I
superconducting films is investigated using magneto-optical imaging. Magnetic
hysteresis with different transition fields for collapse and nucleation of
superconducting domains is found. This is accompanied by topological hysteresis
characterized by the collapse of circular domains and the appearance of
lamellar domains. Magnetic hysteresis is shown to arise from supercooled and
superheated states. Domain-shape instability resulting from long-range magnetic
interaction accounts well for topological hysteresis. Connection with similar
effects in systems with long-range magnetic interactions is emphasized.
