(Hicks’s formula), or
(Ritz’s formula). In many cases this approximation fails for the smaller values of
; and prediction becomes very uncertain, though a plot of the residuals usually gives a smooth curve....
“The principles of selection, which determine what combinations among these numerous terms give rise to observable lines, are very simply expressed in terms of two sets of quantum numbers.
“The azimuthal quantum number (
) is i for all terms of the s-series, 2 for those of the p-series, 3 for the d’s, 4 for the f’s, 5 for the g’s, 6 for the h’s, and so on.
“Combinations usually occur only between terms of adjacent series for which the values of