Letters on England [35]
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 on our eyes from the very
bosom of those pores, that the smaller the pores of a body are the
more such a body is transparent. Thus paper, which reflects the
light when dry, transmits it when oiled, because the oil, by filling
its pores, makes them much smaller.
It is there that examining the vast porosity of bodies, every
particle having its pores, and every particle of those particles
having its own, he shows we are not certain that there is a cubic
inch of solid matter in the universe, so far are we from conceiving
what matter is. Having thus divided, as it were, light into its
elements, and carried the sagacity of his discoveries so far as to
prove the method of distinguishing compound colours from such as are
primitive, he shows that these elementary rays, separated by the
prism, are ranged in their order for no other reason but because
they are refracted in that very order; and it is this property
(unknown till he discovered it) of breaking or splitting in this
proportion; it is this unequal refraction of rays, this power of
refracting the red less than the orange colour, &c., which he calls
the different refrangibility. The most reflexible rays are the most
refrangible, and from hence he evinces that the same power is the
cause both of the reflection and refraction of light.
But all these wonders are merely but the opening of his discoveries.
He found out the secret to see the vibrations or fits of light which
come and go incessantly, and which either transmit light or reflect
it, according to the density of the parts they meet with. He has
presumed to calculate the density of the particles of air necessary
between two glasses, the one flat, the other convex on one side, set
one upon the other, in order to operate such a transmission or
reflection, or to form such and such a colour.
From all these combinations he discovers the proportion in which
light acts on bodies and bodies act on light.
He saw light so perfectly, that he has determined to what degree of
perfection the art of increasing it, and of assisting our eyes by
telescopes, can be carried.
Descartes, from a noble confidence that was very excusable,
considering how strongly he was fired at the first discoveries he
made in an art which he almost first found out; Descartes, I say,
hoped to discover in the stars, by the assistance of telescopes,
objects as small as those we discern upon the earth.
But Sir Isaac has shown that dioptric telescopes cannot be brought
to a greater perfection, because of that refraction, and of that
very refrangibility, which at the same time that they bring objects
nearer to us, scatter too much the elementary rays. He has
calculated in these glasses the proportion of the scattering of the
red and of the blue rays; and proceeding so far as to demonstrate
things which were not supposed even to exist, he examines the
inequalities which arise from the shape or figure of the glass, and
that which arises from the refrangibility. He finds that the object
glass of the
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 on our eyes from the very
bosom of those pores, that the smaller the pores of a body are the
more such a body is transparent. Thus paper, which reflects the
light when dry, transmits it when oiled, because the oil, by filling
its pores, makes them much smaller.
It is there that examining the vast porosity of bodies, every
particle having its pores, and every particle of those particles
having its own, he shows we are not certain that there is a cubic
inch of solid matter in the universe, so far are we from conceiving
what matter is. Having thus divided, as it were, light into its
elements, and carried the sagacity of his discoveries so far as to
prove the method of distinguishing compound colours from such as are
primitive, he shows that these elementary rays, separated by the
prism, are ranged in their order for no other reason but because
they are refracted in that very order; and it is this property
(unknown till he discovered it) of breaking or splitting in this
proportion; it is this unequal refraction of rays, this power of
refracting the red less than the orange colour, &c., which he calls
the different refrangibility. The most reflexible rays are the most
refrangible, and from hence he evinces that the same power is the
cause both of the reflection and refraction of light.
But all these wonders are merely but the opening of his discoveries.
He found out the secret to see the vibrations or fits of light which
come and go incessantly, and which either transmit light or reflect
it, according to the density of the parts they meet with. He has
presumed to calculate the density of the particles of air necessary
between two glasses, the one flat, the other convex on one side, set
one upon the other, in order to operate such a transmission or
reflection, or to form such and such a colour.
From all these combinations he discovers the proportion in which
light acts on bodies and bodies act on light.
He saw light so perfectly, that he has determined to what degree of
perfection the art of increasing it, and of assisting our eyes by
telescopes, can be carried.
Descartes, from a noble confidence that was very excusable,
considering how strongly he was fired at the first discoveries he
made in an art which he almost first found out; Descartes, I say,
hoped to discover in the stars, by the assistance of telescopes,
objects as small as those we discern upon the earth.
But Sir Isaac has shown that dioptric telescopes cannot be brought
to a greater perfection, because of that refraction, and of that
very refrangibility, which at the same time that they bring objects
nearer to us, scatter too much the elementary rays. He has
calculated in these glasses the proportion of the scattering of the
red and of the blue rays; and proceeding so far as to demonstrate
things which were not supposed even to exist, he examines the
inequalities which arise from the shape or figure of the glass, and
that which arises from the refrangibility. He finds that the object
glass of the