Experiments on the Effect of Inhomogeneity and Obliquity of a Magnetic Field in Inhibiting Convection

Two experiments are described on the inhibition of convection in a magnetic field. In the first experiment a layer of mercury is placed in an inhomogeneous magnetic field and heated from below. Photographs show convection where the field is weak, but indicate no motion where the field is strong. The boundary between these two regions corresponds to a critical magnetic field in agreement with current theory. The boundary is well defined showing that the onset of convection is sensitive to variations in the magnetic field. In the second experiment with a homogeneous field, varied in direction from vertical to horizontal, it is the vertical component which controls the onset of motion. A strong horizontal field does not inhibit convection but causes motion in narrow cells elongated in the direction of the field.