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.