  At the "Domus Galilaeana" in Pisa, many original documents and records are
kept, which belong to the scientific activity carried out by Enrico Fermi until
1938. I compared those documentary sources with the supported evidences, the
personal recollections, concerning the discovery that hydrogenated substances
increase the radioactivity induced by neutrons: such a comparison leads to the
conclusion that the discovery occurred on October 20th 1934, i.e., two days
before the date that all the accounts that have been supported so far report.
That suggests that any historical study to come, and regarding the experiments
carried out by Fermi and his group on neutrons, cannot neglect to analyse
carefully the accounts regarding those experiments and to compare them with the
archive records.
