  When a magnetic field is turned on, a superconducting body acquires an
angular momentum in direction opposite to the applied field. This gyromagnetic
effect has been established experimentally and is understood theoretically.
However, the corresponding situation when a superconductor is cooled in a
pre-existent field has not been examined. We argue that the conventional theory
of superconductivity does not provide a prediction for the outcome of that
experiment that does not violate fundamental laws of physics, either Lenz's law
or conservation of angular momentum. The theory of hole superconductivity
predicts an outcome of this experiment consistent with the laws of physics.
