Electric discharges in gases ionization and excitation

In view of the widespread occurrence and the current technical importance of the various manifestations of free electricity in gases, this article appropriately reviews current knowledge concerning the nature of such free charges, how they arise from the normally uncharged atoms and molecules of a gas, and their relation to light radiation. This is the third in a series of special articles developed under the sponsorship of the A.I.E.E. committee on education, and the first of three that will deal with the major divisions of the general subject of electric discharges in gases; the second will deal with the laws governing the movement of free charges through a gas, and the third will discuss known types of discharges in the light of the basic processes which by that time will have been set forth in these columns.