A velocity- and mass-independent search for moving magnetic monopoles is being performed by continuously monitoring the current in a 20-${\mathrm{cm}}^2$-area superconducting loop. A single candidate event, consistent with one Dirac unit of magnetic charge, has been detected during five runs totaling 151 days. These data set an upper limit of 6.1×${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ for magnetically charged particles moving through the earth's surface.

• Received 5 April 1982

DOI:https://doi.org/10.1103/PhysRevLett.48.1378