Copy letter from Michael Foster, to John Sealy Edward Townsend, [Fellow of the Royal Society], Trinity College, Cambridge Before proceeding with the publication of Townsend's paper, 'the diffusion of ions produced in air by the action of a radio-active substance, ultra-violet light and point discharge', Foster requests Townsend goes through the paper and writes in all the symbols and equations in the margin so as to guide the printer. 10 July 1900