If we compare (6) with the relation (1), we see that the connexion with ordinary mechanics in the region of slow vibration, mentioned in the [former section], is satisfied.
Putting
in (3) we get the ordinary series spectrum of hydrogen. Putting
we get a spectrum which, on the theory, should be expected to be emitted by an electron rotating round a helium nucleus. The formula is found very closely to represent some series of lines observed by Fowler[9] and Evans[10]. These series correspond to
and
