Using the 27 kG magnetic field produced by a superconducting solenoid
we have searched for trapped magnetic monopoles in a magnetite sample
from North China. We have scanned the nuclear emulsion both for low io
nizing tracks and heavily ionizing tracks, and polycarbonate track det
ectors for heavily ionizing tracks of magnetic monopoles. We obtained
a 90% confidence level upper limit of 1.8x10(-26) monopoles per nucleo
n in the magnetite sample.