Copy letter from Joseph Larmor, to Mr Birtwistle, Helen's Bay, Belfast Queries if Birtwistle has taken up the physical chemistry matters which Larmor mentioned as feasible. If so he will probably be interested in the enclosed paper [not enclosed]. If he had time Larmor could work on the matter himself on the basis of Planck's papers. There is a good account of such mathematics by H Weber in his new edition of Riemann's P D Equations, but it does not touch this problem. Birtwistle need not return the proof. 31 August 1906