The Spark Spectrum of Neon.

35 kv. as compared to 55 kv. for the arc discharge on an ordinary day. The experiment clearly showed that corona current flow in an atmosphere of high humidity is greatly reduced, and that spark discharges at relatively low voltages are apt to occur. The explanation of this phenomenon very likely is to be found in the reduction of the mobility of negative ions in air of high humidity, although the existence of a thin film of moisture on the electrodes may also play a part. In this connection it may be pointed out that Elster and Geitell have called attention to the fact that the mobility of gas ions in a fog is greatly reduced; also that Tamm2 has found that the mobility of gas ions in air at 100% humidity was approximately 25% of that in dry air. As is well known, with the wires positive with respect to the plate instead of negative, the corona current flow is greatly reduced and spark discharge sets in at a relatively low voltage even on dry days, so that the action of negative wires on wet days was similar to the action of positive wires on dry days, this is very likely due to the fact that humidity reduces the mobility of the negative ions while it leaves the positive ions unaffected.3 1 Ann. Phys., 2, 425 (1900). 2Ibid., 6, 259 (1901). 3 Graetz, Handbuch der Elek. u. Mag., 1923, Seeliger, III, p. 364.