rdinary Light of the day being freely
let in upon them, they immediately disappear: so our Tryals have inform'd
us, that as to the Prismatical Iris painted on the Floor by the beams of
the Sun Trajected through a Triangular-glass; though the Colours of it
appear very Vivid ev'n at Noon-day, and in Sun shiny Weather, yet by a more
Powerfull Light they may be made to disappear. For having sometimes, (in
prosecution of some Conjectures of mine not now to be Insisted on,) taken a
large Metalline Concave _Speculum_, and with it cast the converging Beams
of the Sun upon a Prismatical Iris which I had caus'd to be projected upon
the Floor, I found that the over-powerfull Light made the Colours of the
Iris disappear. And if I so Reflected the Light as that it cross'd but the
middle of the Iris, in that part only the Colours vanish'd or were made
Invisible; those parts of the Iris that were on the right and left hand of
the Reflected Light (which seem'd to divide them, and cut the Iris asunder)
continuing to exhibit the same Colours as before. But upon this we must not
now stay to Speculate.

_EXPERIMENT VII._

I have sometimes thought it worth while to take notice, whether or no the
Colours of Opacous Bodies might not appear to the Eye somewhat Diversify'd,
not only by the Disposition of the Superficial parts of the Bodyes
themselves and by the Position of the Eye in Reference to the Object and
the Light, (for these things are Notorious enough;) but according also to
the Nature of the Lucid Body that shines upon them. And I remember that in
Prosecution of this Curiosity, I observ'd a manifest Difference in some
Kinds of Colour'd Bodyes look'd on by Day-light, and afterwards by the
light of the Moon; either directly falling on them or Reflected upon them
from a Concave Looking-glass. But not finding at present in my Collections
about Colours any thing set down of this Kind, I shall, till I have
opportunity to repeat them, content my self to add what I find Register'd
concerning Colours look'd on by Candle-light, in regard that not only the
Experiment is more easie to be repeated, but the Objects being the Same
Sorts of Colour'd Paper lastly mention'd, the Collation of the two
Experiments may help to make the Conjectures they will suggest somewhat the
less uncertain.

Within a few dayes of the time above mention'd, divers Sheets of Colour'd
Paper that had been look'd upon before in the Sunshine were look'd upon at
night by the