Copenhagen: Jul. Gjellerups Forlag, 1922. First. paperback. Foredrag holdt i Fysisk Forening den 18. Oktober 1921. 70pp. Slim 8vo, original printed wrappers (very lightly worn but sturdy). Kobenhavn: Jul. Gjellerups Forlag, 1922. A very good(+) copy. very good(+).
Bohr wrote this work at the time that he and members of his laboratory staff were working on a theory of the periodic system of the elements. Bohr, by "the analysis of the evidence of the spectra, renewed the science of chemistry by putting at the chemists' disposal rational spectroscopic methods much more refined than the traditional ones. This was dramatically illustrated in 1922, by the identification at Bohr's institute, of the element with atomic number 72..." (DSB), The above work was published the year Bohr received the Nobel Prize in physics.