Photo-electric currents. 
132 Proceedings of the Royal Society of Edinburgh. [Sess. 
It will be noticed that the remaining points observed for carbon dioxide 
fall exactly on the curve for air, showing that the effect of temperature on 
the photo-electric currents in these gases is identical at this pressure. In 
o 100 200 300 400 500 600°C 
Temperatures. 
Fig. 5. 
hydrogen, on the other hand, the photo-electric currents increase steadily 
with the temperature from the first. 
The difference between our results and those of Zeleny is doubtless due 
to the fact that Zeleny was using a voltage far below that required to give 
the saturation current, only 72 volts for a distance of 1*6 cms. ; also to 
the fact that he used as his sensitive electrode a bent piece of platinum 
