The magnetic moment of the nucleus of cæsium

In a previous paper the author investigated the structure of the lines of the principal series of cæsium, and was able to deduce an approximate value for the magnetic moment of the nucleus. This was the first attempt to measure a nuclear magnetic moment; a simple theory was used, requiring a knowledge of the hyperfine structure of the P levels; these could not be observed directly, but their value was estimated from differences in the separations of the hyperfine doublets of the principal series. In the meanwhile, Fermi and Segra and Goudsmid, developing the author’s theory by wave mechanical methods, found more exact formulæ for calculating the nuclear magnetic moment from the structure of the P levels, and also for evaluating this quantity from the hyperfine structure of the S level.