But the same disinclination to repeat myself word for word, or to say the same thing a second time in other and worse words, after I have deprived myself of the better, has occasioned another defect in the first book of this work. For I have omitted all that is said in the first chapter of my essay "On Sight and Colour," which would otherwise have found its place here, word for word. Therefore the knowledge of this short, earlier work is also presupposed.