Spectral sensitivity ofJoshi-effect in chlorine

Summary

Joshi-Effect—an instantaneous and reversible diminution Δi of discharge currenti—is studied in 11 cm. chlorine excited by the silent discharge from 2 to 6 kV of 50 cycles frequency under light from a sodium vapour lamp, that from an incandescent (glass) bulb, directly; and with Wratten and other filters. RelativeJoshi-Effect %Δi=100 Δi/i _p at maximum is 33% sodium light and 72% under unfiltered white. Observed with a thermopile (also with a photo-electric cell) the light intensity lay in the order, unfiltered white (50), violet (13), green (0.1) and red (21). The effect, however, varies, frequencywise. Large Δi under sodium light and red, as observed, support Joshi’s view that Δi is a quantum or frequency effect and not (entirely) a consequence of selective light-adsorption. Under a limited range of conditions, the curves %Δi—mean light frequency (ν) are almost straight lines at a series of kV, which follows simply from Joshi’s theory that a photoelectric effect from an adsorption-like boundary layer formed under the discharge is a primary change precedent to Δi.