This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
A Van de Graaff generator produces some of the highest voltages that can be built on a tabletop, and it does so with a surprisingly simple piece of machinery: a moving belt made of an insulating material, running over two rollers, one near the ground and one inside a large hollow metal sphere mounted on top of an insulating column. Friction between the belt and the lower roller, an effect called the triboelectric effect, the same phenomenon that lets a balloon rubbed on a wool sweater pick up a static charge, strips electrons from one surface and deposits them on the other, leaving the moving belt carrying a steady stream of electric charge. The belt physically carries that charge upward into the hollow sphere, where a comb-shaped metal electrode, positioned close to the belt but not touching it, transfers the charge onto the belt using a phenomenon called corona discharge, in which the electric field near the sharp points of the comb becomes strong enough to ionize the surrounding air and pull charge across the small gap. Because electric charge on a conductor always migrates to the outside surface, the charge delivered inside the sphere immediately moves to the sphere's exterior, which means the interior stays available to receive still more charge from the next section of belt arriving. The process repeats continuously, and the sphere's voltage keeps climbing until the rate at which charge leaks away, through the air or along the supporting column, finally balances the rate at which the belt delivers more. Robert J. Van de Graaff, an American physicist, built his first working version of the device in 1929, originally intending it as a source of high voltage for early nuclear physics experiments that needed to accelerate subatomic particles.