The continuous spectrum of mercury vapour in relation on the resonance line 2536·52

In a former paper it was shown that the continuous spectrum of mercury vapour started as nearly as could be observed from the resonance line 2536·52 IS — Ip 2 , and stretched without intermission from that point to the green region, where it is most conspicuous. This spectrum was obtained by allowing the glowing mercury vapour distilled from the arc to mature by passing it through a long tube; or alternatively by the discharge of an induction coil through mercury vapour which was distilling continuously from the mercury surface, used as cathode of a wide discharge tube. The effect is shown in No. I, Plate 8, reproduced for convenience of reference from that paper. It can hardly be doubted that the continuous spectrum is intimately associated in some way with the resonance line IS — 1p 2 For instance, resonant excitation by the light of this line excites the continuous spectrum as well; in the distillation experiment this line and the continuous spectrumtogether become more prominent relative to all other lines as the luminous vapour matures ; and the excitation potential appears to be nearly or exactly the same for each.