John Ruskin (1855). “Notes on Some of the Principal Pictures Exhibited in the Rooms of the Royal Academy, the Old and New Societies of Painters in Water Colours, the Society of British Artists and the French Exhibition”
John Ruskin (1873). “The Eagle's Nest: Ten Lectures on the Relation of Natural Science to Art, Given Before the University of Oxford in Lent Term, 1872”, p.80