Copy letter from Robert William Frederick Harrison to J W Gordon, Hon. Secretary of the Optical Convention, 113 Broadhurst Gardens, West Hampstead, NW 'In reply to your letter of the 2nd instant, the President desires me to state that he regrets that the Royal Society is unable to contribute apparatus or instruments to the Optical Convention, as the only suitable material we posses is already on loan at the Science Museum, South Kensington.' 16 April 1912