ALS, one page, both sides, 8.5 x 11, September 6, 1952. Handwritten letter to Miss Young, in full: "Thank you very much for sending the manuscript 'Experimental Production of a Divergent Chain Reaction.' I am returning to you the corrected manuscript with the following items. 1—Two copies of the abstract, 2—A list of captions for the figures, 3—An explanatory footnote on p. 3. I am in agreement with the suggestion of the Editor to publish the paper in three instalments. I have prepared captions for all the figures. It seems to me, however, that some of them could be omitted. For example I would suggest to leave out figs. 5, 6, 7 and perhaps figs 4, 5, 7, 9 of appendix 2. On this point I would of course leave the final decision to the Editor. Again I want to thank you very much for your help in this matter.â€Â Fermi has included an additional sheet headed â€Å“Footnote on p. 3, line 5,â€Â which reads: â€Å“The neutron density n varies approximately according to the equation ∇2n = an where a is a constant depending on the physical and geometrical structure of the lattice. The value of a is called the Laplacian of the lattice and is denoted by ∇2. Large values of ∇2 correspond to a letter structure.â€Â In fine to very fine condition.

The production of the first nuclear chain reaction in Chicago-Pile 1 on December 2, 1942, was a major milestone in the eventual utilization of nuclear energy for the economic production of power. In his monthly report of the Physics Division of the Metallurgical Project, Fermi described this historic event very simply: 'The activity of the Physics Division in the past month has been devoted primarily to the experimental production of a divergent chain reaction. The chain reacting structure has been completed on December 2 and has been in operation since then in a satisfactory way. A program of tests on the operating conditions of the chain reacting unit and experiments for the investigation of the various radiations inside and outside the pile is in progress. The results will be reported as soon as possible.'