The prebreakdown mechanism in liquefied nitrogen has been studied by using a modified optical Schlieren system. The present method has the advantage of observing the drift velocity of the disturbance in liquids and the prebreakdown mechanism by using a small disk instead of a knife edge. Thus the disturbance occurring due to the charge carriers can be recorded on the screen with an intensity which is proportional to the rate of the refractive index change. The mobilities of the negatively charged carriers derived from the drift velocity of the disturbance fall in the range of 1.1times;10minus;2ndash;1.85times;10minus;1cm2/Vthinsp;sec at an electric field strength of 9.7times;104V/cm. This value is distinctly larger than that of ions (2.94times;10minus;3cm2/Vthinsp;sec) in liquefied nitrogen, and also that of the quasifree electrons localized in the tiny bubbles (7.95times;10minus;4cm2/Vthinsp;sec) as calculated theoretically.
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