Glass.
These are the principal Ph nomena of thin Plates or Bubbles, whose
Explications depend on the properties of Light, which I have heretofore
deliver'd. And these you see do necessarily follow from them, and agree
with them, even to their very least circumstances; and not only so, but
do very much tend to their proof. Thus, by the 24th Observation it
appears, that the Rays of several Colours, made as well by thin Plates
or Bubbles, as by Refractions of a Prism, have several degrees of
Refrangibility; whereby those of each order, which at the reflexion from
the Plate or Bubble are intermix'd with those of other orders, are
separated from them by Refraction, and associated together so as to
become visible by themselves like Arcs of Circles. For if the Rays were
all alike refrangible, 'tis impossible that the whiteness, which to the
naked Sense appears uniform, should by Refraction have its parts
transposed and ranged into those black and white Arcs.
It appears also that the unequal Refractions of difform Rays proceed not
from any contingent irregularities; such as are Veins, an uneven Polish,
or fortuitous Position of the Pores of Glass; unequal and casual Motions
in the Air or ther, the spreading, breaking, or dividing the same Ray
into many diverging parts; or the like. For, admitting any such
irregularities, it would be impossible for Refractions to render those
Rings so very distinct, and well defined, as they do in the 24th
Observation. It is necessary therefore that every Ray have its proper
and constant degree of Refrangibility connate with it, according to
which its refraction is ever justly and regularly perform'd; and that
several Rays have several of those degrees.
And what is said of their Refrangibility may be also understood of their
Reflexibility, that is, of their Dispositions to be reflected, some at a
greater, and others at a less thickness of thin Plates or Bubbles;
namely, that those Dispositions are also connate with the Rays, and
immutable; as may appear by the 13th, 14th, and 15th Observations,
compared with the fourth and eighteenth.
By the Precedent Observations it appears also, that whiteness is a
dissimilar mixture of all Colours, and that Light is a mixture of Rays
endued with all those Colours. For, considering the multitude of the
Rings of Colours in the 3d, 12th, and 24th Observations, it is manifest,
136