would appear of a pretty good, but yet obscure and dark Sky-colour; the
white between the blue Spots diminishing, until it resembled the Threds
of an irregular Net-work, and soon after vanish'd, and left all the
upper part of the Bubble of the said dark blue Colour. And this Colour,
after the aforesaid manner, dilated it self downwards, until sometimes
it hath overspread the whole Bubble. In the mean while at the top, which
was of a darker blue than the bottom, and appear'd also full of many
round blue Spots, something darker than the rest, there would emerge
one or more very black Spots, and within those, other Spots of an
intenser blackness, which I mention'd in the former Observation; and
these continually dilated themselves until the Bubble broke.
If the Water was not very tenacious, the black Spots would break forth
in the white, without any sensible intervention of the blue. And
sometimes they would break forth within the precedent yellow, or red, or
perhaps within the blue of the second order, before the intermediate
Colours had time to display themselves.
By this description you may perceive how great an affinity these Colours
have with those of Air described in the fourth Observation, although set
down in a contrary order, by reason that they begin to appear when the
Bubble is thickest, and are most conveniently reckon'd from the lowest
and thickest part of the Bubble upwards.
_Obs._ 19. Viewing in several oblique Positions of my Eye the Rings of
Colours emerging on the top of the Bubble, I found that they were
sensibly dilated by increasing the obliquity, but yet not so much by far
as those made by thinn'd Air in the seventh Observation. For there they
were dilated so much as, when view'd most obliquely, to arrive at a part
of the Plate more than twelve times thicker than that where they
appear'd when viewed perpendicularly; whereas in this case the thickness
of the Water, at which they arrived when viewed most obliquely, was to
that thickness which exhibited them by perpendicular Rays, something
less than as 8 to 5. By the best of my Observations it was between 15
and 15-1/2 to 10; an increase about 24 times less than in the other
case.
Sometimes the Bubble would become of an uniform thickness all over,
except at the top of it near the black Spot, as I knew, because it would
exhibit the same appearance of Colours in all Positions of the Eye. And
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