Pearson replies: I am grateful to Ruth Sime for raising the issue of the incorrect positioning of element 93 in the periodic table. I intended to do so in the original article but space limitations prevented it. (A longer version of the article can be found at But one might ask whether the outcome would have been any different even if the transuranics had been correctly positioned in the periodic table: Would Enrico Fermi have then taken Ida Noddack more seriously? Conceivably not, since he failed to address another problem—namely, that the observed multiplicity of half-lives was serving as a warning that something more complex than a simple radiative capture of neutrons was taking place. Actually, in his Nature paper,1 Fermi was very cautious in claiming that he had formed transuranics: It was his successors who accepted that interpretation uncritically, even as the anomalies accumulated.

Concerning Lise Meitner, the object of my article was not to attribute credit for the eventual discovery of fission but rather to understand why it took so long. In that respect I must remind the reader of Meitner’s 1936 rebuff of Fritz Strassmann when he reported finding barium in neutron-irradiated uranium: “Leave that to us physicists, and throw your results in the garbage can.” Meitner’s earlier opposition to the very suggestion of fission makes all the more remarkable the assurance she gave to Otto Hahn in late 1938, as Sime mentions. That assurance is discussed in more detail in Sime’s biography of Meitner (Lise Meitner: A Life in Physics, page 235), but one wonders whether Meitner was recalling Noddack’s proposal from long before, probably without even identifying the source of her memory.

As for Sime’s last point, I did not intend to suggest that Hahn had explicitly promised to include Meitner’s name on the paper with Strassmann, had she come up with a physical explanation. I certainly believed, though, that such a promise was implicit in his request to the exiled Meitner seeking her advice on his puzzling results. However, a closer reading of Hahn’s letter of 19 December 1938 to Meitner (see, for example, pages 233–34 of Sime’s biography) shows that I was wrong: Hahn expresses the hope that Meitner will have something to publish on her own, so that “it would still in a way be work by the three of us!” Presumably Hahn wrote that for precisely the reasons Sime states in her letter; he acted in the only way that was open to him at the time. Any suggestion of deceit on his part at this stage would be inappropriate.