The dark interval in mercury fluorescence

This phenomenon was originally described by R. W. Wood. He found that when a rapidly moving current of mercury vapour was excited by the aluminium spark, the green fluorescence did not start at the point at which excitation was applied, but that as interval could be observed in which the vapour was dark. He also found that the fluorescence of wave-length 2537 corresponding to the resonance line, which accompanies the green fluorescence, showed a dark interval. Some other authors have also written on this effect. Pienkowski obtained it under certain conditions with mercury arc excitation, but left it open whether the excitation was to be considered atomic or molecular. It has also been discussed by Gaviola. It seemed that further work was called for since the dark interval phenomenon may be crucial for determining the real relationship between the numerous and complicated phenomenon of mercury fluorescence.