yet when numbers of these Thrids are brought together into one Skein, their Colour becomes notorious.
9. But the same Occasion that invited me to say what I have mention'd concerning the Leaves of Trees, invites me also to give you some account of what happens in Changeable Taffities, where we see differing Colours, as it were, Emerge and Vanish upon the Ruffling of the same piece of Silk: As I have divers times with Pleasure observ'd, by the help of such a Microscope, as, though it do not very much Magnifie the Object, has in recompence this great Conveniency, that you may easily, as fast as you please, remove it from one part to another of a Large Object, of which the Glass taking a great part at once, you may thereby presently Survey the Whole. Now by the help of such a Microscope I could easily (as I began to say) discern, that in a piece of Changeable Taffity, (that appear'd, for Instance, sometimes Red, and sometimes Green) the Stuff was compos'd of Red thrids and Green, passing under and over each other, and crossing one another in almost innumerable points; and if I look'd through the Glass upon any considerable portion of the Stuff, that (for example sake) to the
naked Eye appear'd to be Red, I could plainly see, that in that Position, the Red thrids were Conspicuous, and reflected a vivid Light; and though I could also perceive, that there were Green ones, yet by reason of their disadvantagious Position in the Physical Surface of the Taffity, they were in part hid by the more Protuberant Thrids of the other Colour; and for the same cause, the Reflection from as much of the Green as was discover'd, was comparatively but Dim and Faint. And if, on the contrary, I look'd through the Microscope upon any part that appear'd Green, I could plainly see that the Red thrids were less fully expos'd to the Eye, and obscur'd by the Green ones, which therefore made up the Predominant Colour. And by observing the Texture of the Silken Stuff, I could easisy so expose the Thrids either of the one Colour or of the other to my Eye, as at pleasure to exhibit an apparition of Red or Green, or make those Colours succeed one another: So that, when I observ'd their Succession by the help of the Glass, I could mark how the Predominant Colour did as it were start out, when the Thrids that exhibited it came to be advanagiously plac'd; And by making little Folds in the Stuff after a certain manner,
the Sides that met and terminated in those Folds, would appear to the naked Eye, one of them Red, and the other Green. When Thrids of more than two differing Colours chance to be Interwoven, the resulting changeableness of the Taffity may be also somewhat different. But I choose to give an Instance in the Stuff I have been speaking off, because the mixture being more Simple, the way whereby the Changeableness is produc'd, may be the more easily apprehended: and though Reason alone might readily enough lead a considering Man to guess at the Explication, in case he knew how Changeable Taffities are made: yet I thought it not impertinent to mention it, because both Scholars and Gentlemen are wont to look upon the Inquiry into Manufactures, as a Mechanick imployment, and consequently below Them; and because also with such a Microscope as I have been mentioning, the discovery is as well Pleasant as Satisfactory, and may afford Hints of the Solution of other Phænomena of Colours. And it were not amiss, that some diligent Inquiry were made, whether the Microscope would give us an account of the Variableness of Colour, that is so Conspicuous and so Delightfull in Mother of Pearl, in Opalls, and some
other resembling Bodies: For though I remember I did formerly attempt something of that Kind (fruitlesly enough) upon Mother of Pearl, yet not having then the advantage of my best Microscope, nor some Conveniences that might have been wish'd, I leave it to you, who have better Eyes, to try what you can do further; since 'twill be Some discovery to find, that, in this case, the best Eyes and Microscopes themselves can make None.
10. I confess, Pyrophilus, that a great part of what I have deliver'd, (or propos'd rather) concerning the differing forms of Asperity in Bodies, by which Differences the incident Light either comes to be Reflected with more or less of Shade, and with that Shade more or less Interrupted, or else happens to be also otherwise Modify'd or Troubl'd, is but Conjectural. But I am not sure, that if it were not for the Dullness of our Senses, either these or some other Notions of Kin to them, might be better Countenanc'd; for I am apt to suspect, that if we were Sharp sighted enough, or had such perfect Microscopes, as I fear are more to be wish'd than hop'd for, our promoted Sense might discern in the Physical Surfaces of Bodies, both a great many latent Ruggidnesses, and the particular
Sizes, Shapes, and Situations of the extremely little Bodies that cause them, and perhaps might perceive among other Varieties that we now can but imagine, how those little Protuberances and Cavities do Interrupt and Dilate the Light, by mingling with it a multitude of little and singly undiscernable Shades, though some of them more, and some of them less Minute, some less, and some more Numerous; according to the Nature and Degree of the particular Colour we attribute to the Visible Object; as we see, that in the Moon we can with Excellent Telescopes discern many Hills and Vallies, and as it were Pits and other Parts, whereof some are more, and some less Vividly illustrated, and others have a fainter, others a deeper Shade, though the naked Eye can discern no such matter in that Planet. And with an Excellent Microscope, where the Naked Eye did see but a Green powder, the Assisted Eye as we noted above, could discern particular Granules, some of them of a Blew, and some of them of a Yellow colour, which Corpuscles we had beforehand caus'd to be exquisitly mix'd to compound the Green.
11. And, Pyrophilus, that you may not think me altogether extravagant in what I
have said of the Possibility, (for I speak of no more) of discerning the differing forms of Asperity in the Surfaces of Bodies of several Colours, I'l here set down a Memorable particular that chanc'd to come to my Knowledge, since I writ a good part of this Essay; and it is this. Meeting casually the other Day with the deservedly Famous[4] Dr. J. Finch, Extraordinary Anatomist to that Great Patron of the Virtuosi, the now Great Duke of Toscany, and enquiring of this Ingenious Person, what might be the chief Rarity he had seen in his late return out of Italy into England, he told me, it was a Man at Maestricht in the Low-Countrys, who at certain times can discern and distinguish Colours by the Touch with his Fingers. You'l easily Conclude, that this is farr more strange, than what I propos'd but as not Impossible; since the Sense of the Retina seeming to be much more Tender and quick than that of those Grosser Filaments, Nerves or Membranes of our Fingers, wherewith we use to handle Gross and Hard Bodies, it seems scarce credible, that any Accustomance, or Diet, or peculiarity of Constitution, should enable a Man to distinguish
with such Gross and Unsuitable Organs, such Nice and Subtile Differences as those of the forms of Asperity, that belong to differing Colours, to receive whose Languid and Delicate Impressions by the Intervention of Light, Nature seems to have appointed and contexed into the Retina the tender and delicate Pith of the Optick Nerve. Wherefore I confess, I propos'd divers Scruples, and particularly whether the Doctor had taken care to bind a Napkin or Hankerchief over his Eyes so carefully, as to be sure he could make no use of his Sight, though he had but Counterfeited the want of it, to which I added divers other Questions, to satisfie my Self, whether there were any Likelihood of Collusion or other Tricks. But I found that the Judicious Doctor having gone farr out of his way, purposely to satisfie Himself and his Learned Prince about this Wonder, had been very Watchfull and Circumspect to keep Himself from being Impos'd upon. And that he might not through any mistake in point of Memory mis-inform Me, he did me the Favour at my Request, to look out the Notes he had Written for his Own and his Princes Information, the summ of which Memorials, as far as we shall mention them here, was this, That the Doctor