Berlin, Germany: Julius Springer, 1926. Hardcover. First Edition. viii, 948 pp, 8vo. Volume is ex-library with brown patterned paper boards, lighter brown cloth spines and corner tips; gold embossed titling to spine. Wear to edges of cover boards where cloth has worn to reveal board beneath, hinge cloth beginning to split at front and rear cover but still tight to boards. Library stamps within, including stamps on title page of each volume, very clean with card pocket remaining on the rear pastedown of each volume. All text in German. Very Good.
“Über die Spektra von Atomsystemen mit zwei Elektronen” by Werner Heisenberg (pp. 499-518) outlines the experiment in which Heisenberg refined the principle of "exchange interaction"