Unpublished note, 'Reply of Mr Buchanan to my queries respecting the patterns of ribbon' by [Whitlock Nicholl] Nicholl summarises an experiment performed on [Archibald] Buchanan whose account of his own colour blindness is found at AP/9/16/5. Nicholl asked Buchanan to describe ribbon samples corresponding to colours of the rainbow by daylight and by candlelight, recording his perceptions of the colours. Nicholl includes the ribbon samples, each covered with its own paper flap, that he used to test Buchanan. Subject: Physiology 4 February 1818