Studies of Light Absorption under Conditions productive of Joshi Effect in Mercury Vapour under Ozoniser Discharge

A new phenomenon called Joshi effect ( Δ i ) which involved a marked diminution of gaseous conductivity under irradiation, was described. Data for the production of Δ i corresponding to 100 per cent photorediction of the conductivity in mercury vapour excited by potentials near `threshold potential' V m , were presented. Light absorption of mercury vapour was studied against hydrogen discharge when a fine absorption line occurred at 2536Å whose intensity remained sensibly the same for the excited vapour; that excited near V m , and also when irradiated to give appreciable Δ i . Results using the tungsten lamp and mercury arc also showed no noticeable difference between normal and excited vapour under conditions causing large Δ i . It is considered that Joshi effect is not a consequence of selective light absorption by the gaseous phase.