The Effect of the ElecU'ic DiscJiarge on Water Vajjonr. 155 
As the pressure under which the vapour is admitted approaches the 
critical value for which the coloration is unstable when the discharge is 
passed, the falling off of the pressure of gas after the maximum has been 
reached diminishes. With the disappearance of the last traces of colour 
the falling off ceases altogether. The passage of the discharge through 
vapour under pressures greater than the critical pressure causes a rapid 
increase in the pressure of gas formed, but the pressure does not pass 
through a maximum ; its highest value is a permanent value. These 
highest values do not vary greatly until the pressure under which the 
vapour is admitted approaches saturation pressure. But the time taken 
to reach these highest values increases as the pressure under which the 
vapour is admitted becomes greater. When this last approaches saturation 
pressure, these highest values begin to increase rapidly and linearly with 
the pressure under which the vapour is admitted, until this quantity 
attains to the value of saturation pressure. 
The value of the maximum pressure of gas formed when the discharge 
is passed through vapour under saturation pressure, appears to be inde- 
pendent of the value of the saturation pressure, up to a definite critical 
value of this quantity. For values greater than this critical value, the 
maximum pressure of gas formed decreases as the saturation pressure 
increases. 
The writer's thanks are due to Mr. W. H. Logeman, M.A., for his help 
and suggestions in the course of the research. 
