Unpublished letter, regarding colour blindness from Arch [Archibald] Buchanan to Whitlock Nicholl Buchanan, a colour blind man studied by Nicholl, writes of the appearance of his eyes and his difficulties in distinguishing green from red, certain shades of yellow from brown, and pink and purple from blue. He then describes his perceptions of common objects, such as grass, fruit, lobsters, and cucumbers. He does not believe anyone else in his family is colour blind apart from a niece, but states that a neighbour seems to have a similar condition. He promises to forward Nicholl's letter to this neighbour. Subject: Physiology Written by Buchanan in Catrine Bank near Mauchline [East Ayrshire, Scotland] and addressed to Nicholl in Ludlow, Shropshire [England]. 4 February 1818