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