Voltage-Intensity Relations of Mercury Lines Below Ionization

Accelerating voltage-intensity relations have been obtained for twenty-eight lines of the mercury spectrum (between 5500A and 2500A) excited by electronic bombardment at potentials less than the ionization potential. The tube in which the radiation was excited had four electrodes, hot cathode and three grids, and the observations were made by photographic spectrophotometric measurements. In agreement with the results of other workers, the minimum potential of excitation of a line is found to agree closely with the theoretical value in all cases but one. The curves representing the voltage-intensity relation for lines with a common outer orbit are found identical when the intensity scales are so chosen as to arbitrarily make the curves coincide at one point. Upward and downward breaks are found in these curves at certain critical potentials but the character of the breaks and the potentials at which they occur change from series to series. The ratio of the numbers of quanta emitted in the lines of the triplet $2p_1-2s\left(5461\right)\mathrm{}$, $2p_2-2s\left(4358\right)\mathrm{}$, $2p_3-2s\left(4047\right)\mathrm{}$ with an accelerating voltage of 10.2 volts was found to be 9:11:3.