PRODUCTION OF THE JOSHI EFFECT IN OXYGEN UNDER SILENT  ELECTRIC DISCHARGE, PART I. INFLUENCE OF THE EXCITING  POTENTIAL AND THE GAS PRESSURE

The Joshi effect, Δ\(i\), an instantaneous and reversible photo-variation (usually, diminution) of the discharge current i in gases, has been studied in oxygen in the range 10-500 mm. Hg (p) and excited by ozoniser discharges over 0.5 to 6 kilo-volts (V) of so cycles frequency. 'Threshold potential' V_m, at which i increases rapidly with V, varies sensibly linearly with p. Well below Vm, Δ\(i\) is not detected. Above Vm, Δ\(i\) at constant p first increases with V and then decreases. The relative effect, % Δ\(i\), is a maximum near Vm, and diminishes thereafter. The potential distribution in respect of both pt and % Δ\(i\) is flat at higher p, which is significant for the pressure-dependence of the mechanism of Δ\(i\). The authors' observation under a wide range of conditions of up to 50% current decrease in oxygen under bat visible light suggests that the Joshi effect is not a special reaction limited to excited halogens; The generality of results are in accord with Joshi's theory of this phenomenon.