Fluorescent excitation of mercury by the resonance frequency and by lower frequencies. III

In pursuing this subject further, the method has been, as before, to investigate closely such points as presented themselves in experiment. Theory does not afford as yet more than a limited guidance, and indeed some of the observed facts seem difficult to reconcile with received views. It has been found that some of the distinctions drawn in II between the results of wing and core excitation must be qualified. Core excitation is defined as that produced by the atomic resonance line, as from a cooled mercury lamp. Wing excitation is due to molecular absorption in the absorption region outside the resonance line, on the side of long waves. For this the iron arc has usually been used as a source. The core effect is most definitely distinguished from the wing effect by the fact that the former is extinguished by a trace of hydrogen, while the latter is unaffected by adding even a large amount of hydrogen. Hydrogen destroys the 21 P3 excited atoms, which, in the core effect, are the first stage towards excited molecules.