Space Charge and Current in Alternating Corona

1. The physical nature of ionization in a corona discharge in air is studied; by means of the corona spectrum, the saturation current in air around the corona voltage, and the influence of the material of the wire on the saturation current. The results indicate that nitrogen only is ionized in a corona discharge in air; that the ionization of the nitrogen results in the separation of an electron from the nitrogen molecule; and that the electron quickly attaches to a molecule or group of molecules, probably water or oxygen, to form an ion. 2. The free charge in the neighborhood of the wire called the space charge, is found to be alternating in character and to have a definite boundary. The space charge formed on any half-wave returns to the wire on the next succeeding half-wave. 3. The mobility of the ions is calculated from the boundary of the space charge. A limiting value of about 10 cm./sec. per volt/cm. is indicated for the positive ions. The negative ions show no sign of a limiting value and the mobility varies from about 1.6 to 10 cm./sec. per volt/cm. as the maximum impressed voltage rises from the corona voltage to twice the corona voltage. 4. Ionization is found to occur at lower voltages on the positive half-waves than on the negative half-waves and the ionization on the positive half-waves becomes much more copious with the beginning of ionization on the negative half-waves. 5.