Calcium spectral frequencies

By closely studying the work of Kirchoff and Bunsen, Hinrichs found that some of the spectral hne frequencies, those referred to as dark hnes, could be related to the chemistry of the elements through their atomic weights, as well as to their postulated atomic dimensions. The difference between the spectral line frequencies seemed to be inversely proportional to the atomic weights of the elements in question. Hinrichs quoted the values of calcium, where the frequency difference is 4.8 units, and barium, which is chemically similar but has a higher atomic weight and shows a frequency difference of 4.4 units." ... 

Moseley devised an apparatus which enabled the X-rays generated by firing electrons at a metallic target in a cathode ray tube to be diffracted by a crystal of potassium ferrocyanide and the resulting spectral lines to be recorded photographically. Moseley found that each element produced its own characteristic set of X-ray lines, and he commented that the method makes the analysis of X-rays as simple as any other branch of spectroscopy. In his first paper Moseley measured the frequencies of one of the characteristic lines in the X-ray spectra of the elements from calcium to zinc (with the exception of scandium). He found that the frequency of the lines was proportional to Q, where Q increased by a constant amount between consecutive elements when ordered according to the periodic table. Moseley continued ... 

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