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The effect of a magnetic field on impulse flashover voltages along the surface of a solid insulator set in a low-pressure neon gas is described. The test vessel is of right cylindrical shape with a height of 34 mm and is made of hard glass. The bottom plate, with 5 mm thick glass is used as the solid insulator. A high voltage electrode and an earthed electrode are set on the periphery and at the centre of the upper side of the bottom plate, respectively. A thin metal sheet with the same area as the bottom plate is put just beneath the bottom plate to serve as a back electrode. A magnetic field, with a flux density of up to 1 T, is applied perpendicularly to the bottom plate. For a positive impulse, when the high voltage electrode is ring-shaped, the flashover voltage increases gradually with the increase in magnetic flux density after showing an abrupt reduction at about 10-2 T, whereas the flashover voltage increases steadily in the case of a negative impulse. When the high voltage electrode is point-shaped, the flashover voltage increases steadily with the increase in magnetic flux density regardless of the polarity of the applied impulse voltages.