Observations on the Excitation of Helium Spectra

IN the course of an examination of the properties of the electron discharge in an atmosphere of helium we have made some observations of the conditions affecting the excitation of the lines of the helium spectra which seem to be of considerable interest. The source of electrons was an incandescent tungsten filament, and the discharge passed to a parallel nickel wire about 8 mm. distant. The electrodes were mounted in a quartz tube filled with helium at about 2 mm. pressure. The helium was free from all contaminants except a small amount of mercury vapour, the partial pressure of which was about 0.001 mm. in the observations immediately following.