Oscillator strengths f3/2n and f1/2 n for the principal series of rubidium are calculated using relativistic wave functions obtained by means of the relativistic parametric-potential method. Three different approaches are used pointing out that the separation between relativistic and correlation effects is not unique and somewhat arbitrary. The calculations were carried out up to the principal quantum number n = 80 showing that the ratio Rn = f3/2n / f1/2 n increases rapidly with n towards a limiting value, a result in agreement with a recent experiment on highly excited Rydberg states.
Fluorescence has been excited in sodium vapor at 180\ifmmode^\circ\else\textdegree\fi{}C by illuminating with the second member of the principal series, $\ensuremath{\lambda}=3303\mathrm{A}$. Both the first and second members of the principal series appeared in the fluorescence, the first member being due to the atom returning to its normal state in steps. The ratio of the intensities of the two lines was determined by photographic photometry and the results compared with what might be expected on the basis of measurements by Weiss on the sodium arc. In the arc the atom returns to the normal state from the
3P by way of the
2S twentyfive times as often as the direct transition occurs whereas in fluorescence approximately the same number take each path. This is contrary to the usual assumption that the transition probabilities are independent of the method of excitation.