Opticks 1717 - Up

which between the fame G&es exhibited the
i:mc Colour, as 4 to 3, arid’sby the 21it Obfervation
the Colours of thinJBodies,are not varied
by var ing the ambient Medium; the thickqY.s
o ry a B~bblc of Water, exhibiting any Co-
I~uT, will be -$ of1 the thicknefs of Air produtjing
the fame Colour. And fo according to
qhe fame 10th and zxit Obfervations the thicknefs
of a Plate of Glafs, whafe Refra&ian of
the mean refrangible Ray, is me&red by the
proportion of the Sines 31 to 20, may be 9 of
the thicknefs of Air producing the fame Colours
; and the like of other Mediums. I do
not affirm, that this proportian of 20 to 3r,
* holds in all the Rays ; for the Sines of other
Sorts of Rays have other Proportions. But the
differences of thofe Proportions arc fo little
. that I do not here confider them. On thefe
Grounds I phave compofed the following Table,
wherein the thicknefs of Air, Wateri and.
,, Glafs, at which each Colour is molt intenl’c
ind fpecifick, is exprefled in parts’ of an Inch
: divided into ten hundred thouiand equal parts.