Large ledger labelled on cover 'P.M.S. Blackett. The Cavendish Laboratory, Cambridge, A', with lists of rolls of film. Entries bgein in January 1929. Careful event by event analysis of collision of alpha-particle tracks with helium. Numerous closely-written pages of measurements, calculations, summaries of results. Pp. 55-59, 'Collision of H particles with gas atoms'. 1929