Firing time of an igniter type of tube

The time interval required for ignition or “firing” of an igniter type of rectifier tube is found to vary in a statistically systematic manner between successive operations. When in continuous operation with igniter rod potential gradients greater than a critical value the median firing time is an inverse exponential function of the gradient in the rod. If the gradient be reduced gradually below the critical value the firing time rapidly approaches infinity, corresponding to failure to ignite at all. Temperature rise of the rod caused by continuous operation of the tube results in a marked reduction in resistance, critical gradient, and median firing time.