The Light of a Fire tinges every thing it illumines, with Yellow; but this does never ap pear, excepting when view'd in opposition to some other thing enlighten'd by the Air. It may be observ'd towards the close of the Day, and better about the Dawn, or in a dark Room; where a Ray being reflected from the Air, and another emitted from a Fire, or Candle, upon the same Object, their difference will be very plain and obvious. But without thus opposing them to each other, their difference wou'd be scarcely sensible; nor without this Method wou'd it be easy to distinguish between several Colours which bear a near affinity to each other; as for instance, White and Yellow, Sea-Green and Azure; for in effect, the Light illumining the Air, being Yellowish, tinges the Blue into a kind of Green, which may be further improved into a very beautiful Green, by the mixture of a little more Yellow.