_MADAM,_
Concerning the comparison, your _Author_ makes between an Immaterial
Spirit, and Light,[1] That, _as Light is contractive and dilative, and
yet not divisible, so is also an Immaterial substance._ Give me leave
to tell you, that in my opinion, all that is contractive and dilative,
is also dividable, and so is light: As for example; when a Candle is
snuff'd, the Snuffers do not onely clip the wick, but also the light:
The like when a dark body is interposed, or crosses the rays of the
Sun; it cuts those rays asunder, which by reason they cannot joyn
together again, because of the interposed body, the light cut off,
suddenly goeth out; that is, the matter of light is altered from the
figure of light, to some other thing, but not annihilated: And since no
more light can flow into the room from the Fountain or Spring of Light,
the Sun, because the passage is stopt close, the room remaineth dark:
For Light is somewhat of the nature of Water; so long as the Spring
is open, the Water flows, and whatsoever is taken away, the Spring
supplies; and if another body onely presses thorow it, it immediately
joyns and closes its severed parts again, without any difficulty or
loss; The same doth Light; onely the difference is, that the substance
of Light is extraordinary rare, and pure; for as Air is so much rarer
then Water, so Light is so much rarer and purer then Air, and its
matter may be of so dilating a nature, as to dilate from a point into
numerous rayes. As for ordinary Fire-light, it doth not last longer,
then it hath fuel to feed it, and so likewise it is with the light
of the Sun; for Light is according to the substance that feeds it;
and though it is a substance it self, yet it increases and decreases,
according as it hath something that succours or nourishes it. But some
may object, that if Light were a body, and did contract and dilate, as
I say, it is impossible that it could display it self in so great and
vast a compass, and remove so suddenly and instantly as it doth. To
which objection, I answer, first, That although I say, Light is a real
corporeal substance, and doth contract and dilate it self from a point
into numerous rayes, as also in another Letter I sent you before,[2]
That Light and Darkness do succeed each other; nevertheless, as for the
perception of Light, I am not so eager in maintaining this opinion,
as if it was an Infallible Truth, and impossible to be otherwise; but
I say onely, That, to my sense and reason, it seems very probable,
that it may be so, that the light of the Sun doth really dilate it
self into so vast a compass as we see, and that light and darkness do
really succeed each other, as all other Creatures do: But yet it seems
also probable to mee, that the parts of the Air may onely pattern
out the figure of light, and that the light we see in the Air may be
onely patterns taken from the real figure of the light of the Sun: And
therefore, if it be according to the former opinion, to wit, That the
light of the Sun doth really dilate it self into so vast a compass, My
answer is, That contraction and dilation are natural corporeal actions
or motions, and that there is no alteration of motion in Nature, but
is done in Time, that is, successively, not instantly; for Time is
nothing else but the alteration of motion: Besides, I do not perceive
any so sudden and swift alteration and succession of light, but that
it is done by degrees: As for example; in the morning, when it begins
to dawn and grow light, it appears clearly to our sight how light doth
come forth, and darkness remove by degrees; and so at night, when it
grows dark, how light removes, and darkness succeeds; nay, if there
be any such sudden change of the motions of Light, I desire you to
consider, _Madam_, that light is a very subtil, rare, piercing and
active body, and therefore its motions are much quicker then those of
grosser bodies, and cannot so well be perceived by our gross exterior
senses. But if it be, that the Air doth pattern out the light of the
Sun, then the framed objection can prove nothing, because there is not
then such a real dilation or succession of light, but the corporeal
figurative motions of the Air do make patterns of the light of the
Sun, and dissolve those patterns or figures again, more suddenly and
quickly then man can shut and open his eyes, as being more subtil
then his gross exterior senses. But it may be said, that if Air did
pattern out the light of the Sun, the light would increase by these
numerous patterns. I answer, that cannot appear to our Eyes; for we
see onely the pattern'd figure of light, and that a great compass is
enlightned; also that the further the air is from the Sun, the darker
it is; nevertheless, I do verily believe, that the body of the Sun is
far brighter then the light we see, and that the substance of light,
and the patterns taken from light, are not one and the same, but very
different. And thus much of light. As for Penetration, I conceive it
to be nothing else but division; as when some parts pierce and enter
through other parts, as Duellers run each other thorow, or as water
runs through a sieve. And this is the opinion of,
Madam,
_Your faithful Friend,_
_and Servant._
[1] _In the Append. to the Antid. c._ 3. and _Of the Immortality of the
Soul, l._ 1. _c._ 5.
[2] _Sect._ 1. _Let._ 20.