6 Autograph letters signed to Samuel Goudsmit. 13 pp. total

His Scientific Archives Were Destroyed in a Bombing Raid; Only 189 Letters Survive, of which the Five Offered Here are Previously Unknown Paschen, Friedrich (1865-1947). 6 Autograph letters signed to Samuel Goudsmit (1902-78). Charlottenburg or Berlin, January 15, 1932-June 13, 1935. 13pp. total on 7 sheets measuring either 237 x 208 mm. or 286 x 223 mm. Creased where previously folded, with minor soiling and wear along creases, otherwise fine. English translations included. Excellent series of very technical scientific letters to Goudsmit discussing his ongoing investigations in spectroscopy, particularly problems of hyperfine structure and the Zeeman effect. Described by one biographer as "probably the greatest experimental spectroscopist of his time" (quoted in DSB), Paschen, in the words of Niels Bohr, had a "happy intuition" that led him always to "pursue experimentally those problems the investigation of which proved to be of decisive significance for the extension of general theoretical conceptions" (quoted in DSB). Paschen's experimental work in spectroscopy provided some of the most revealing clues to atomic structure; it was particularly useful to Arnold Sommerfeld, whose modifications of Bohr's theory of atomic structure had impressed Paschen so much that he devoted six months to confirming the theory's predictions. During his tenure as professor of physics at the University of Tubingen (1901-24), Paschen made Tubingen into Germany's most important center of atomic spectroscopy. In 1924 he succeeded Nernst as president of the Physikalische-Technische Reichsanstalt, the highest post to which a German experimental physicist could aspire; on May 1, 1933, after the Nazi's seizure of power in Germany, he was forced to retire in favor of the pro-Nazi physicist Johannes Stark. Despite this setback, Paschen was able to continue his laboratory research for a few years afterward-although at the cost of considerable difficulty and personal humiliation, some of which is hinted at in the letters offered here. These six letters from Paschen to Goudsmit are almost exclusively concerned with the scientific investigations performed by the two men during the years 1932-1935; they exemplify the interplay between theoretical and experimental physics so characteristic of Paschen's career. This is particularly apparent in the last four letters (August 22, 1933-June 13, 1935), in which Paschen provided Goudsmit with detailed information on the results of his latest researches: Thank you so much for kindly sending me your and Mr. Bacher's work on anomalies in hyperfine structures. At the same time please accept my cordial congratulations on your wonderful quantitative settlement of the disputed questions regarding Al II and Hg I. For Al everything now appears to be in perfect order. Also, in the meantime I have become convinced that two fine structure components of the two lines 4 1,3F3-nG are simple and do not have any weak companions. Accordingly, the term nG must be split with 0.48 cm-1, as you conclude, and not with 0.35 as I assumed. . . . It is fascinating how the same problem is approached independently from several angles. However, your work is very important because you derive quantitative, definitive results. And in his letter of Aug. 22, 1933: You were so kind to write me concerning the theoretical fundamentals for comprehending the fine structures of the lines of Al II. Since you went to such trouble, I assume that the progress of my work on this topic would be of interest to you and would like to inform you that the publication thereof will not be forthcoming for some time. . . . I have made a study of extensive new material and have progressed to the point that the entire spectrum can be based quite soundly on the values of the fine structure terms. . . . All triplet terms now have two different numerical values corresponding to j + 1/2 and j - 1/2, which are based on the fine structure splitting values that you provided. . .…