It is not impossible that Aristotle's enumeration of the colours may have been derived from, or confirmed by, this very experiment. Speaking of the after-image of colours he says, "The impression not only exists in the sensorium in the act of perceiving, but remains when the organ is at rest. Thus if we look long and intently on any object, when we change the direction of the eyes a responding colour follows. If we look at the sun, or any other very bright object, and afterwards shut our eyes, we shall, as if in ordinary vision, first see a colour of the same kind; this will presently be changed to a red colour, then to purple, and so on till it ends in black and disappears."--_De Insomniis_. [1] "Geschichte der Farbenlehre," in the "Nachgelassene Werke." Cotta, 1833. [2] The treatise in question is ascribed by Goethe to Theophrastus, but it is included in most editions of Aristotle, and even attributed to him in those which contain the works of both philosophers; for instance, in the Aldine Princeps edition, 1496. Calcagnini says, the treatise is made up of two separate works on the subject, both by Aristotle. [3] His authority seems to have been equally great on subjects connected with the phenomena of vision; the Italian translator of a Latin treatise, by Portius, on the structure and colours of the eye, thus opens his dedication to the Cardinal Ercole Gonzaga, of Mantua:--"Grande anzi quasi infinito è l'obligo che ha il mondo con quel più divino che umano spirito di Aristotile." [4] In a letter to Ziegler the mathematician, Calcagnini speaks of Raphael as "the first of painters in the theory as well as in the practice of his art." This expression may, however, have had reference to a remarkable circumstance mentioned in the same letter, namely, that Raphael entertained the learned Fabius of Ravenna as a constant guest, and employed him to translate Vitruvius into Italian. This MS. translation, with marginal notes, written by Raphael, is now in the library at Munich. "Passavant, Rafael von Urbino." [5] Lodovico Dolce's Treatise on Colours (1565) is in the form of a dialogue, like his "Aretino." The abridged theory of Aristotle is followed by a translation of the Treatise of Antonius Thylesius on Colours; this is adapted to the same colloquial form, and the author is not acknowledged: the book ends with an absurd catalogue of emblems. The "Somma della Filosofia d'Aristotile," published earlier by the same author, is a very careless performance.