Opticks 1717 - Up

Wards the center, e ‘b(h$ ii+ red
and yellows
Now as all thefe things follow’ f't0111 the pro+
per-ties of Light by $ mathematical %Vay of reak
Coning, fo the truth of them may be.mamfe{~ecj
by Experiments, For in a dark @.OOl$ .by view-.’
&j thefe Kings through .a Priiin, by scflexiori
.of the feverql prifmatick Col0Ul~S,’ ‘~I$11 ,an
afflfiani caufes to’ move to and fro upok a Wall
,or Paper from whence they are pefletted, wj61$
the $$j&htor’s Eye8 d&e Prifnn and the obJe&L
ges (as in the x3 th Obfervation)
dy: the Pofition pf the Circles
.eeiTiveIy by the ‘feveral Colours , wi
fuch, in refpe& of ‘one another, as
fcribed in the Figures 2 b x v 7 ‘or a b XV,
op
+p 5 T, And by the fame method the truth of
the Explications of other Obfervations may be
gxamined.
I3 what hath been kid, the like Phznqmena
nf $ ater, and thin Plates of Glakmay be unk
~erO.o,od. But in fina1.l fragments of thofe J?lates,
there is this farther obfervable, that where they
lye flat upon a ‘Table and are turned about their
centers whilit they are viewed through a Pr$q
they will, in fame pofiures exhibit ‘Waves of va:
rious Colours,, and fame of therq exhibit thefe
Wav& in one or two Pofitions only, but the,
,~~~ofi,of them do in all Poiitions exhibit them?
,and make them for the melt, part appear al?
DN$E dl over the .P)lates, The reafon is) that,
the $!.lyerfkies of filch yj.ates are not even, but
have mat~y. Cavities and ‘Swellin& which how
jhlloW
. ,, ‘.I foever $0, %*< little ., .I vary 8,’ the ,‘.” thicknefs I ,. of
$g