Referee's report by Paytrick Maynard Stuart Blackett, on a paper 'Showers produced by the penetrating cosmic radiation' by W Heitler Sectional committee: Physics Feels he is not competent enough to report on the paper. Makes some comments on the parts he understands. If the opinions of Dirac and Peierls are favourable the paper should be published. He doesn't like the formulation of the theory, but this is due to his bias against elaborate mathematical theories that ignore relevant facts. A theory like this requires a more thorough discussion of the physical principles. [Published in Proceedings of the Royal Society A, 1938]. Endorsed on verso as received 23 March 1938. 21 March 1938