Referee's report by Nevill Francis Mott, on a paper 'Reciprocity failure of photographic materials at short exposure times' by W F Berg Sectional Committee: Physics Recommended for publication in the 'Proceedings of the Royal Society of London'. Suggests adding legends to the figures. Has no issue with his identity being revealed to the author, as they have already discussed the paper. [Published in the 'Proceedings of the Royal Society of London'] Endorsed on recto as received 12 December 1939. [December 1939]