The other of these Wedges, I fill'd with a most lovely tincture of Copper,
drawn from the filings of it, with spirit of _Urine_, and this Wedge held
as the former against the Light, afforded all manner of Blues, from the
faintest to the deepest, so that I was in good hope by these two, to have
produc'd all the varieties of colours imaginable; for I thought by this
means to have been able by placing the two _Parallelogram_ sides together,
and the edges contrary ways, to have so mov'd them to and fro one by
another, as by looking through them in several places, and through several
thicknesses, I should have compounded, and consequently have seen all those
colours, which by other like compositions of colours would have ensued.

But insteed of meeting with what I look'd for, I met with somewhat more
admirable; and that was, that I found my self utterly unable to see through
them when placed both together, though they were transparent enough when
asunder; and though I could see through twice the thickness, when both of
them were fill'd with the same colour'd liquors, whether both with the
Yellow, or both with the Blue, yet when one was fill'd with the Yellow, the
other with the Blue, and both looked through, they both appear'd dark,
onely when the parts near the tops were look'd through, they exhibited
Greens, and those of very great variety, as I expected, but the Purples and
other colours, I could not by any means make, whether I endeavour'd to look
through them both against the Sun, or whether I plac'd them against the
hole of a darkned room.

But notwithstanding this mis-ghessing, I proceeded on with my trial in a
dark room, and having two holes near one another, I was able, by placing my
Wedges against them, to mix the ting'd Rays that past through them, and
fell on a sheet of white Paper held at a convenient distance from them as I
pleas'd; so that I could make the Paper appear of what colour I would, by