Experimentally it is found that hydrogen is necessary for the generation of radio-frequency current, but that numerous cathodes, generally of even atomic number, may be used. The spectrum of the oscillating arc shows the Balmer series and the first spark spectrum of the cathode. With the cathode sufficiently hot, the cathode lines disappear, leaving a strong Balmer series on a continuous background. All oscillating arcs of the Poulsen type have about the same high-frequency limit, viz., 5×${10}^6$ cycles per sec (60 meters).

• Received 11 May 1929

DOI:https://doi.org/10.1103/PhysRev.34.978