In a Composition, as well as in every Single Figure, or other part of which the Picture consists, one thing must Contrast, or be varied from another. Thus in a Figure, the Arms and Legs must not be placed to answer one another in Parallel Lines. In like manner if one Figure in a Composition Stands, another must Bend, or Lye on the Ground ; and of those that Stand, or are in any other Position, if there be several of them, they must be varied by Turns of the Head, or some other Artful Disposition of their Parts ; as may be seen (for instance) in the Carton of giving the Keys. The Masses must also have the like Contrast, two must not be alike in Form, or Size, nor the whole Mass compos’d of those lesser ones of too Regular a Shape. The Colours must be also Contrasted, and Oppos’d, so as to be grateful to the Eye : There must not (for example) be two Draperies in one Picture of the same Colour, and Strength, unless they are contiguous, and then they are but as one. If there be two Reds, Blews, or whatever other Colour, One must be of a Darker, or Paler Tinct, or be some way Varied by Lights, Shadows, of Reflections. Rafaëlle, and others have made great Advantage of Changeable Silks to unite the Contrasting Colours, as well as to make a part of the Contrast themselves. As in the Carton of Giving the Keys, the Apostle that stands in Profile, and immediately behind S. John, has a Yellow Garment with Red Sleeves, which connects that Figure with S. Peter, and S. John, whose Draperies are of the same Species of Colours. Then the same Anonymous Apostle has a loose changeable Drapery, the Lights of which are a Mixture of Red, and Yellow, the other Parts are Bluish. This Unites it self with the Other Colours already mentioned, and with the Blew Drapery of another Apostle which follows afterwards ; between which, and the changeable Silk is a Yellow Drapery something different from the other Yellows, but with Shadows bearing upon the Purple, as those of the Yellow Drapery of S. Peter incline to the Red : All which, together with several other Particulars, produce a wonderful Harmony.