The Surface of every Opake Body, partakes of the Colour of the Body that enlightens it. This appears in the Instance of dark Bodies, none of which show either their Figure or Colour, unless the Medium between the Body and the Light, be illumined: If the Opake Body therefore be Yellow, and that whence the Light comes Blue, the illumined part of the Opake Body must of consequence be Green; that being the Result of Blue and Yellow mingled together.