action, in like
manner as a long staff acts at one end when pushed forward by the other.
That light is certainly darted by the sun; in fine, that light is
transmitted from the sun to the earth in about seven minutes, though a
cannonball, which were not to lose any of its velocity, could not go that
distance in less than twenty-five years. How great would have been his
astonishment had he been told that light does not reflect directly by
impinging against the solid parts of bodies, that bodies are not
transparent when they have large pores, and that a man should arise who
would demonstrate all these paradoxes, and anatomise a single ray of
light with more dexterity than the ablest artist dissects a human body.
This man is come. Sir Isaac Newton has demonstrated to the eye, by the
bare assistance of the prism, that light is a composition of coloured
rays, which, being united, form white colour. A single ray is by him
divided into seven, which all fall upon a piece of linen, or a sheet of
white paper, in their order, one above the other, and at unequal
distances. The first is red, the second orange, the third yellow, the
fourth green, the fifth blue, the sixth indigo, the seventh a
violet-purple. Each of these rays, transmitted afterwards by a hundred
other prisms, will never change the colour it bears; in like manner, as
gold, when completely purged from its dross, will never change afterwards
in the crucible. As a superabundant proof that each of these elementary
rays has inherently in itself that which forms its colour to the eye,
take a small piece of yellow wood, for instance, and set it in the ray of
a red colour; this wood will instantly be tinged red. But set it in the
ray of a green colour, it assumes a green colour, and so of all the rest.

From what cause, therefore, do colours arise in Nature? It is nothing
but the disposition of bodies to reflect the rays of a certain order and
to absorb all the rest.

What, then, is this secret disposition? Sir Isaac Newton demonstrates
that it is nothing more than the density of the small constituent
particles of which a body is composed. And how is this reflection
performed? It was supposed to arise from the rebounding of the rays, in
the same manner as a ball on the surface of a solid body. But this is a
mistake, for Sir Isaac taught the astonished philosophers that bodies are
opaque for no other reason but because their pores are large, that light
reflects o