Spherical bubble model of an H II region in a magnetic field. The field is oriented to the upper right and out of the page, inclined 30° to the line of sight. The arrows at (a) and (b) represent the local magnetic field at two points as might be deduced from Zeeman splitting. The line‐of‐sight projection of the magnetic field is out of the page outside the dotted curve, as at (a), and into the page inside the curve, as at (b). In the limiting cases of the magnetic field aligned along (perpendicular to) the line of sight, the line‐of‐sight direction of the field is reversed over none (half) of the projected area of the sphere. For a uniform distribution of magnetic field directions intersecting a sphere at all possible angles, on average the line‐of‐sight direction of the magnetic field is reversed over 25% of the area of the projected sphere.