Letter from Henry Edward Armstrong, 55 Granville Park, Lewisham, London, to [John Hall] Gladstone A proof of Gladstone's paper has set him thinking and he believes an further line of investigation might be opened. Notes some indication of a 'co-operative influence', as he has argued in the production of colour. Thinks it useless to discuss the matter on stage at the Physical [Society] as 'physicists are so frightfully ignorant of the higher chemistry of the day'. 15 February 1893