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.
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