Moseley's k_2 \ was given as a general empirical constant to fit either the K-alpha line which was the most intense line as judged by observation of the spectrum, or the L-alpha transition line being a visually weaker-intensity line found in X-ray element spectra.
f \left(L_\alpha \right) = \left(3.29 \times 10^{15}\right) \times 5/36 \times \left(Z - 7.4\right)^2 Hz .