The densities of the principal lines of the singlet and triplet systems of molecular hydrogen, as well as ${\mathrm{H}}_{\alpha }$, ${\mathrm{H}}_{\beta }$, and ${\mathrm{H}}_{\gamma }$ were measured for electronic velocities in the range 19 to 220 equivalent volts, the electron emission and the gas pressure being kept constant. The triplet lines have no maximum density in this range but seem to be approaching one slightly below 19 volts. All the singlet lines show a decided maximum of density between 30 and 35 volts. The densities of ${\mathrm{H}}_{\alpha }$, ${\mathrm{H}}_{\beta }$ and ${\mathrm{H}}_{\gamma }$ decrease very rapidly below 30 volts indicating that the number of dissociating collisions which produce an excited atom must be very small at 19 volts. The use of curves showing the variation in the ratio of the densities of singlet and triplet lines with voltage is suggested as a method for finding the mean electronic velocities in certain types of gaseous discharges.

• Received 22 May 1929

DOI:https://doi.org/10.1103/PhysRev.34.431