PICOSECOND DISCHARGES AND STICK-SLIP FRICTION AT A MOVING MENISCUS OFMERCURY ON GLASS

At a meeting of the French Academy in 1700, Bernoulli demonstrated tha t swirling mercury in an evacuated flask generates light(1,2). He emph asized that this 'barometer light' ''has not been explained since its discovery about 30 years ago'' by Picard(3). Here we revisit this phen omenon and find that the repetitive emission of Light from mercury mov ing over glass is accompanied by the collective picosecond transfer of large numbers of electrons, When brought into contact with mercury, t he glass acquires a net charge. This charge separation provides a forc e which, in our experiment in a rotating flask, drags mercury against gravity in the direction of the motion of the glass. Eventually the ed ge of the mercury slips relative to the glass, accompanied by a picose cond electrical discharge and a flash of light. This repetitive build- up and discharge of static electricity thus gives rise to stick-slip m otion, The statistics of the intervals between events and their respec tive magnitudes are history-dependent and are not yet understood.