It conduces also something to the confirmation of this Proposition,
that, according to the 22d Observation, the Colours exhibited by the
denser thin Body within the rarer, are more brisk than those exhibited
by the rarer within the denser.
PROP. VII.
_The bigness of the component parts of natural Bodies may be conjectured
by their Colours._
For since the parts of these Bodies, by _Prop._ 5. do most probably
exhibit the same Colours with a Plate of equal thickness, provided they
have the same refractive density; and since their parts seem for the
most part to have much the same density with Water or Glass, as by many
circumstances is obvious to collect; to determine the sizes of those
parts, you need only have recourse to the precedent Tables, in which the
thickness of Water or Glass exhibiting any Colour is expressed. Thus if
it be desired to know the diameter of a Corpuscle, which being of equal
density with Glass shall reflect green of the third Order; the Number
16-1/4 shews it to be (16-1/4)/10000 parts of an Inch.
The greatest difficulty is here to know of what Order the Colour of any
Body is. And for this end we must have recourse to the 4th and 18th
Observations; from whence may be collected these particulars.
_Scarlets_, and other _reds_, _oranges_, and _yellows_, if they be pure
and intense, are most probably of the second order. Those of the first
and third order also may be pretty good; only the yellow of the first
order is faint, and the orange and red of the third Order have a great
Mixture of violet and blue.
There may be good _Greens_ of the fourth Order, but the purest are of
the third. And of this Order the green of all Vegetables seems to be,
partly by reason of the Intenseness of their Colours, and partly because
when they wither some of them turn to a greenish yellow, and others to a
more perfect yellow or orange, or perhaps to red, passing first through
all the aforesaid intermediate Colours. Which Changes seem to be
effected by the exhaling of the Moisture which may leave the tinging
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