Letter from Rudolf Ernst Peierls, on a paper 'Kinetic theory of diffusion in gases and liquids. II. General kinetic theory of liquids mixtures' by L M Yang to D C Martin, Assistant Secretary of the Royal Society Section six has no been expanded and is more intelligible. He is now convinced that it it wrong in the send that the approximations used are not justified. However, the papers shouldn't be turned down on this accord. He is still worried about the writing of the two equations but this is a matter for the Assistant Editor to decide. [Published in Proceedings of the Royal Society A, 1949]. Endorsed on recto as received 22 March 1949. 19 March 1949