Letter from Patrick Maynard Stuart Blackett, Baron Blackett of Chelsea, to John David Griffith Davies, regarding a paper 'The production of cosmic-ray bursts by mesotrons' by C B O Mohr and Godfrey Harry Stafford Sectional Committee: Physics Notes a mistake in the calibration factor of the ionisation chamber. Thinks some of the quantities may be wrong. Suggests adding standard errors to the diagrams. Refers to work by J Franklin Carlson and Marcel Schein, Harold Albert Wilson and Walter Heinrich Heitler. Gives details of calibration. Suggests consulting with the comunicator Harrie Stewart Wilson Massey. [Published in the 'Proceedings of the Royal Society of London'] Endorsed on recto as received 2 October 1942. 1 October 1942