Cabrera counts flux quanta to find a Dirac monopole

Take a superconducting loop, place it in an ultralow magnetic‐field device, and monitor the current with a Superconducting Quantum Interference Device for many months. That was the experiment that Blas Cabrera of Stanford University did in his search for a moving magnetic monopole. On Valentine's Day he found a single event consistent with one Dirac unit of magnetic charge. When rumors of the observation spread, the organizers of the Third Workshop on Grand Unification phoned Cabrera in Blacksburg, Virginia (where he was giving a colloquium), and asked him to address the Workshop the next morning (16 April). After a long, wee‐hours‐of‐the‐morning drive to Chapel Hill, N. C., Cabrera electrified the workshop participants with his careful, low‐key account of his possible monopole discovery.