Copy letter from Robert William Frederick Harrison to Messrs Longmans, Green & Co 'I am unable to identify 3 figures from the list of blocks which Sir Wm Abney wishes to see use in his book on Trichnomatic Vision. The following is a transcript of the information respecting them given on the list. 1. Diagram of the modified apparatus III ! 1892 Fig 1. Diagram of the colour patch apparatus. 2. also a small cut bellow [handwritten diagram]. 3. Transactions: [?] of eye to light a colour (1897) fig 8 p 303.' 5 January 1912