Experiment XIX
To ſhew the Chymiſts, that Colours may be made to Appear or Vaniſh, where there intervenes no Acceſſion or Change either of the Sulphureous, or the Saline, or the Mercurial principle (as they ſpeak) of Bodies: I ſhall not make uſe of the Iris afforded by the Glaſs-priſm, nor of the Colours to be ſeen in a fair Morning in thoſe drops of Dew that do in a convenient manner Reflect and Refract the Beams of Light to the Eye; But I will rather mind them of what they may obſerve in their own Laboratories, namely, that divers, if not all, Chymical Eſſential Oyls, as alſo good Spirit of Wine, being ſhaken till they have good ſtore of Bubbles, thoſe Bubbles will (if attentively conſider’d) appear adorn’d with various and lovely Colours, which all immediately Vaniſh, upon the relapſing of the Liquor that affords thoſe Bubbles their Skins, into the reſt of the Oyl, or Spirit of Wine, ſo that a Colourleſs Liquor may be made in a trice to exhibit variety of Colours, and may loſe them in a moment without the Acceſſion or Diminution of any of its Hypoſtatical Principles. And, by the way, ’tis not unworthy our notice, that ſome Bodies, as well Colourleſs, as Colour’d, by being brought to a great Thinneſs of parts, acquire Colours though they had none before, or Colours differing from them they were before endued with: For, not to inſiſt on the Variety of Colours, that Water, made ſomewhat Glutinous by Sope, acquires, when ’tis blown into ſuch Sphærical Bubbles as Boys are wont to make and play with; Turpentine (though it have a Colour deep enough of its own) may (by being blown into after a certain manner) be brought to afford Bubbles adorn’d with variety of Orient Colours, which though they Vaniſh after ſome while upon the breaking of the Bubbles, yet they would in likelihood always exhibit Colours upon their Superfices, (though not always the ſame in the ſame Parts of them, but Vary’d according to the Incidence of the Sight, and the Poſition of the Eye) if their Texture were durable enough: For I have ſeen one that was Skill’d at faſhioning Glaſſes by the help of a Lamp, blowing ſome of them ſo ſtrongly as to burſt them, whereupon it was found, that the Tenacity of the Metall was ſuch, that before it broke it ſuffer’d it ſelf to be reduc’d into Films ſo extremely thin, that being kept clean they conſtantly ſhew’d on their Surfaces (but after the manner newly mention’d) the varying Colours of the Rain-bow, which were exceedingly Vivid, as I had often opportunity to obſerve in ſome, that I caus’d purpoſely to be made, to keep by me.
But leſt it ſhould be objected, that the above mentioned Inſtances are drawn from Tranſparent Liquors, it may poſſibly appear, not impertinent to add, what I have ſometimes thought upon, and ſeveral times tried, when I was conſidering the Opinions of the Chymiſts about Colours, I took then a Feather of a convenient Bigneſs and Shape, and holding it at a fit diſtance betwixt my Eye and the Sun when he was near the Horizon, me thought there appear’d to me a Variety of little Rain-bows, with differing and very vivid Colours, of which none was conſtantly to be ſeen in the Feather; the like Phænomenon I have at other times (though not with altogether ſo good ſucceſs) produc’d, by interpoſing at a due diſtance a piece of Black Ribband betwixt the almoſt ſetting Sun and my Eye, not to mention the Trials I have made to the ſame purpoſe, with other Bodies.