484 Mr. A. B. Meservey on the Potentials required 



A few sets of readings were taken with aluminium and 

 platinum electrodes inside, but they showed no consistent 

 differences from those obtained with brass. It seemed as if 

 there might be some effect due to difference of material, but 

 if so, it was different in air from what it was in hydrogen. 



Fig. 4. 





Pvessuvc in Km 



In fig. 5 the sparking potential is plotted against the 

 diameter of the inner cylinder for a constant pressure of 

 1*5 mm. of mercury. The sparking potentials for parallel 

 plates at distances equal to those between the cylinders for 



