  A passive magnetic shield was designed and constructed for magnetometer tests
for the future neutron electric dipole moment experiment at TRIUMF. The axial
shielding factor of the magnetic shield was measured using a magnetometer based
on non-linear magneto-optical rotation of the plane of polarized laser light
upon passage through a paraffin-coated vapour cell containing natural Rb at
room temperature. The laser was tuned to the Rb D1 line, near the $^{85}$Rb
$F=2\rightarrow 2,3$ transition. The shielding factor was measured by applying
an axial field externally and measuring the magnetic field internally using the
magnetometer. The axial shielding factor was determined to be $(1.3\pm
0.1)\times 10^{7}$, from an applied axial field of 1.45~$\mu$T in the
background of Earth's magnetic field.
