I know not whether you will think it Inconſiderable to annex to this Experiment, That we obſerv'd in a Room not Darken'd, that the Priſmatical Iris (if I may ſo call it) might be Reflected without loſing any of its ſeveral Colours (for we now conſider not their Order) not onely from a plain Looking-glaſs and from the calm Surface of Fair Water, but alſo from a Concave Looking-glaſs; and that Refraction did as little Deſtroy thoſe Colours as Reflection. For by the help of a large (double Convex) Burning-glaſs through which we Refracted the Suns Beams, we found that one part of the Iris might be made to appear either beyond, or on this ſide of the other Parts of the ſame Iris; but yet the ſame Vivid Colours would appear in the Diſplac'd part (if I may ſo term it) as in the other. To which I ſhall add, that having, by hiding the ſide of the Priſm, obverted to the Sun with an Opacous Body, wherein only one ſmall hole was left for the Light to paſs through, reduc'd the Priſmatical Iris (caſt upon White Paper) into a very narrow compaſs, and look'd upon it througn a Microſcope; the Colours appear'd the ſame as to kind that they did to the naked Eye.
EXPERIMENT VI.
It may afford matter of Speculation to the Inquiſitive, ſuch as you, Prophilus, that as the Colours of outward Objects brought into a Darken'd Room, do ſo much depend for their Viſibility upon the Dimneſs of the Light they are there beheld by; that the ordinary 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 light of a pretty big Candle, (ſnuff'd) and the Changes that were obſerv'd were theſe.