immediate objects of sight are not so much as the ideas or resemblances of
things placed at a distance, it is requisite that we look nearer into the
matter, and carefully observe what is meant in common discourse when one
says, that which he sees is at a distance from him. Suppose, for example,
that looking at the moon I should say it were fifty or sixty semidiameters
of the earth distant from me. Let us see what moon this is spoken of. It
is plain it cannot be the visible moon, or anything like the visible moon,
or that which I see—which is only a round luminous plain, of about thirty
visible points in diameter. For, in case I am carried from the place where
I stand directly towards the moon, it is manifest the object varies still
as I go on; and, by the time that I am advanced fifty or sixty
semidiameters of the earth, I shall be so far from being near a small,
round, luminous flat that I shall perceive nothing like it—this object
having long since disappeared, and, if I would recover it, it must be by
going back to the earth from whence I set out(323). Again, suppose I
perceive by sight the faint and obscure idea of something, which I doubt
whether it be a man, or a tree, or a tower, but judge it to be at the
distance of about a mile. It is plain I cannot mean that what I see is a
mile off, or that it is the image or likeness of anything which is a mile
off; since that every step I take towards it the appearance alters, and
from being obscure, small, and faint, grows clear, large, and vigorous.
And when I come to the mile’s end, that which I saw first is quite lost,
neither do I find anything in the likeness of it(324).
45. In these and the like instances, the truth of the matter, I find,
stands thus:—Having of a long time experienced certain ideas perceivable
by touch(325)—as distance, tangible figure, and solidity—to have been
connected with certain ideas of sight, I do, upon perceiving these ideas
of sight, forthwith conclude what tangible ideas are, by the wonted
ordinary course of nature, like to follow. Looking at an object, I
perceive a certain visible figure and colour, with some degree of
faintness and other circumstances, which, from what I have formerly
observed, determine me to think that if I advance forward so many paces,
miles, &c., I shall be affected with such and such ideas of touch. So
that, in truth and strictness of speech, I neither see distance itself,
nor anything that I take to be at a distance. I say, neither distance nor
things placed at a distance are themselves, or their ideas, truly
perceived by sight. This I am persuaded of, as to what concerns myself.
And I believe whoever will look narrowly into his own thoughts, and
examine what he means by saying he sees this or that thing at a distance,
will agree with me, that what he sees only suggests to his understanding
that, after having passed a certain distance, to be measured by the motion
of his body, which is perceivable by touch(326), he shall come to perceive
such and such tangible ideas, which have been usually connected with such
and such visible ideas. But, that one might be deceived by these
suggestions of sense, and that there is no necessary connexion between
visible and tangible ideas suggested by them, we need go no farther than
the next looking-glass or picture to be convinced. Note that, when I speak
of tangible ideas, I take the word idea for any the immediate object of
sense, or understanding—in which large signification it is commonly used
by the moderns(327).
46. From what we have shewn, it is a manifest consequence that the ideas
of space, outness(328), and things placed at a distance are not, strictly
speaking, the object of sight(329); they are not otherwise perceived by
the eye than by the ear. Sitting in my study I hear a coach drive along
the street; I look through the casement and see it; I walk out and enter
into it. Thus, common speech would incline one to think I heard, saw, and
touched the same thing, to wit, the coach. It is nevertheless certain the
ideas intromitted by each sense are widely different, and distinct from
each other; but, having been observed constantly to go together, they are
spoken of as one and the same thing. By the variation of the noise, I
perceive the different distances of the coach, and know that it approaches
before I look out. Thus, by the ear I perceive distance just after the
same manner as I do by the eye.
47. I do not nevertheless say I hear distance, in like manner as I say
that I see it—the ideas perceived by hearing not being so apt to be
confounded with the ideas of touch as those of sight are. So likewise a
man is easily convinced that bodies and external things are not properly
the object of hearing, but only sounds, by the mediation whereof the idea
of this or that body, or distance, is suggested to his thoughts. But then
one is with more difficulty brought to discern the difference there is
betwixt the ideas of sight and touch(330): though it be certain, a man no
more sees and feels the same thing, than he hears and feels the same
thing.
48. One reason of which seems to be this. It is thought a great absurdity
to imagine that one and the same thing should have any more than one
extension and one figure. But, the extension and figure of a body being
let into the mind two ways, and that indifferently, either by sight or
touch, it seems to follow that we see the same extension and the same
figure which we feel.
49. But, if we take a close and accurate view of the matter, it must be
acknowledged that we never see and feel one and the same object(331). That
which is seen is one thing, and that which is felt is another. If the
visible figure and extension be not the same with the tangible figure and
extension, we are not to infer that one and the same thing has divers
extensions. The true consequence is that the objects of sight and touch
are two distinct things(332). It may perhaps require some thought rightly
to conceive this distinction. And the difficulty seems not a little
increased, because the combination of visible ideas hath constantly the
same name as the combination of tangible ideas wherewith it is
connected—which doth of necessity arise from the use and end of
language(333).
50. In order, therefore, to treat accurately and unconfusedly of vision,
we must bear in mind that there are two sorts of objects apprehended by
the eye—the one primarily and immediately, the other secondarily and by
intervention of the former. Those of the first sort neither are nor appear
to be without the mind, or at any distance off(334). They may, indeed,
grow greater or smaller, more confused, or more clear, or more faint. But
they do not, cannot approach, [or even seem to approach (335)] or recede
from us. Whenever we say an object is at a distance, whenever we say it
draws near, or goes farther off, we must always mean it of the latter
sort, which properly belong to the touch(336), and are not so truly
perceived as suggested by the eye, in like manner as thoughts by the ear.
51. No sooner do we hear the words of a familiar language pronounced in
our ears but the ideas corresponding thereto present themselves to our
minds: in the very same instant the sound and the meaning enter the
understanding: so closely are they united that it is not in our power to
keep out the one except we exclude the other also. We even act in all
respects as if we heard the very thoughts themselves. So likewise the
secondary objects, or those which are only suggested by sight, do often
more strongly affect us, and are more regarded, than the proper objects of
that sense; along with which they enter into the mind, and with which they
have a far more strict connexion than ideas have with words(337). Hence it
is we find it so difficult to discriminate between the immediate and
mediate objects of sight, and are so prone to attribute to the former what
belongs only to the latter. They are, as it were, most closely twisted,
blended, and incorporated together. And the prejudice is confirmed and
riveted in our thoughts by a long tract of time, by the use of language,
and want of reflection. However, I doubt not but anyone that shall
attentively consider what we have already said, and shall say upon this
subject before we have done (especially if he pursue it in his own
thoughts), may be able to deliver himself from that prejudice. Sure I am,
it is worth some attention to whoever would understand the true nature of
vision.
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52. I have now done with Distance, and proceed to shew how it is that we
perceive by sight the Magnitude of objects(338). It is the opinion of some
that we do it by angles, or by angles in conjunction with distance. But,
neither angles nor distance being perceivable by sight(339), and the
things we see being in truth at no distance from us(340), it follows that,
as we have shewn lines and angles not to be the medium the mind makes use
of in apprehending the apparent place, so neither are they the medium
whereby it apprehends the apparent magnitude of objects.
53. It is well known that the same extension at a near distance shall
subtend a greater angle, and at a farther distance a lesser angle. And by
this principle (we are told) the mind estimates the magnitude of an
object(341), comparing the angle under which it is seen with its distance,
and thence inferring the magnitude thereof. What inclines men to this
mistake (beside the humour of making one see by geometry) is, that the
same perceptions or ideas which suggest distance do also suggest
magnitude. But, if we examine it, we shall find they suggest the latter as
immediately as the former. I say, they do not first suggest distance and
then leave it to the judgment to use that as a medium whereby to collect
the magnitude; but they have as close and immediate a connexion with the
magnitude as with the distance; and suggest magnitude as independently of
distance, as they do distance independently of magnitude. All which will
be evident to whoever considers what has been already said and what
follows.
54. It has been shewn there are two sorts of objects apprehended by sight,
each whereof has its distinct magnitude, or extension—the one, properly
tangible, i.e. to be perceived and measured by touch, and not immediately
falling under the sense of seeing; the other, properly and immediately
visible, by mediation of which the former is brought in view. Each of
these magnitudes are greater or lesser, according as they contain in them
more or fewer points, they being made up of points or minimums. For,
whatever may be said of extension in abstract(342), it is certain sensible
extension is not infinitely divisible(343). There is a _minimum
tangibile_, and a _minimum visibile_, beyond which sense cannot perceive.
This every one’s experience will inform him.
55. The magnitude of the object which exists without the mind, and is at a
distance, continues always invariably the same: but, the visible object
still changing as you approach to or recede from the tangible object, it
hath no fixed and determinate greatness. Whenever therefore we speak of
the magnitude of any thing, for instance a tree or a house, we must mean
the tangible magnitude; otherwise there can be nothing steady and free
from ambiguity spoken of it(344). Now, though the tangible and visible
magnitude do in truth belong to two distinct objects(345), I shall
nevertheless (especially since those objects are called by the same name,
and are observed to coexist(346)), to avoid tediousness and singularity of
speech, sometimes speak of them as belonging to one and the same thing.
56. Now, in order to discover by what means the magnitude of tangible
objects is perceived by sight, I need only reflect on what passes in my
own mind, and observe what those things be which introduce the ideas of
greater or lesser into my thoughts when I look on any object. And these I
find to be, _first_, the magnitude or extension of the visible object,
which, being immediately perceived by sight, is connected with that other
which is tangible and placed at a distance: _secondly_, the confusion or
distinctness: and _thirdly_, the vigorousness or faintness of the
aforesaid visible appearance. _Cæteris paribus_, by how much the greater
or lesser the visible object is, by so much the greater or lesser do I
conclude the tangible object to be. But, be the idea immediately perceived
by sight never so large, yet, if it be withal confused, I judge the
magnitude of the thing to be but small. If it be distinct and clear, I
judge it greater. And, if it be faint, I apprehend it to be yet greater.
What is here meant by confusion and faintness has been explained in sect.
35.
57. Moreover, the judgments we make of greatness do, in like manner as
those of distance, depend on the disposition of the eye; also on the
figure, number, and situation(347) of intermediate objects, and other
circumstances that have been observed to attend great or small tangible
magnitudes. Thus, for instance, the very same quantity of visible
extension which in the figure of a tower doth suggest the idea of great
magnitude shall in the figure of a man suggest the idea of much smaller
magnitude. That this is owing to the experience we have had of the usual
bigness of a tower and a man, no one, I suppose, need be told.
58. It is also evident that confusion or faintness have no more a
necessary connexion with little or great magnitude than they have with
little or great distance. As they suggest the latter, so they suggest the
former to our minds. And, by consequence, if it were not for experience,
we should no more judge a faint or confused appearance to be connected
with great or little magnitude than we should that it was connected with
great or little distance.
59. Nor will it be found that great or small visible magnitude hath any
necessary relation to great or small tangible magnitude—so that the one
may certainly and infallibly be inferred from the other. But, before we
come to the proof of this, it is fit we consider the difference there is
betwixt the extension and figure which is the proper object of touch, and
that other which is termed visible; and how the former is principally,
though not immediately, taken notice of when we look at any object. This
has been before mentioned(348), but we shall here inquire into the cause
thereof. We regard the objects that environ us in proportion as they are
adapted to benefit or injure our own bodies, and thereby produce in our
minds the sensations of pleasure or pain. Now, bodies operating on our
organs by an immediate application, and the hurt and advantage arising
therefrom depending altogether on the tangible, and not at all on the
visible, qualities of any object—this is a plain reason why those should
be regarded by us much more than these. And for this end [chiefly(349)]
the visive sense seems to have been bestowed on animals, to wit, that, by
the perception of visible ideas (which in themselves are not capable of
affecting or anywise altering the frame of their bodies), they may be able
to foresee(350) (from the experience they have had what tangible ideas are
connected with such and such visible ideas) the damage or benefit which is
like to ensue upon the application of their own bodies to this or that
body which is at a distance. Which foresight, how necessary it is to the
preservation of an animal, every one’s experience can inform him. Hence it
is that, when we look at an object, the tangible figure and extension
thereof are principally attended to; whilst there is small heed taken of
the visible figure and magnitude, which, though more immediately
perceived, do less sensibly affect us, and are not fitted to produce any
alteration in our bodies.
60. That the matter of fact is true will be evident to any one who
considers that a man placed at ten foot distance is thought as great as if
he were placed at the distance only of five foot; which is true, not with
relation to the visible, but tangible greatness of the object: the visible
magnitude being far greater at one station than it is at the other.
61. Inches, feet, &c. are settled, stated lengths, whereby we measure
objects and estimate their magnitude. We say, for example, an object
appears to be six inches, or six foot long. Now, that this cannot be meant
of visible inches, &c. is evident, because a visible inch is itself no
constant determinate magnitude(351), and cannot therefore serve to mark
out and determine the magnitude of any other thing. Take an inch marked
upon a ruler; view it successively, at the distance of half a foot, a
foot, a foot and a half, &c. from the eye: at each of which, and at all
the intermediate distances, the inch shall have a different visible
extension, i.e. there shall be more or fewer points discerned in it. Now,
I ask which of all these various extensions is that stated determinate one
that is agreed on for a common measure of other magnitudes? No reason can
be assigned why we should pitch on one more than another. And, except
there be some invariable determinate extension fixed on to be marked by
the word inch, it is plain it can be used to little purpose; and to say a
thing contains this or that number of inches shall imply no more than that
it is extended, without bringing any particular idea of that extension
into the mind. Farther, an inch and a foot, from different distances,
shall both exhibit the same visible magnitude, and yet at the same time
you shall say that one seems several times greater than the other. From
all which it is manifest, that the judgments we make of the magnitude of
objects by sight are altogether in reference to their tangible extension.
Whenever we say an object is great or small, of this or that determinate
measure, I say, it must be meant of the tangible and not the visible
extension(352), which, though immediately perceived, is nevertheless
little taken notice of.
62. Now, that there is no necessary connexion between these two distinct
extensions is evident from hence—because our eyes might have been framed
in such a manner as to be able to see nothing but what were less than the
_minimum tangibile_. In which case it is not impossible we might have
perceived all the immediate objects of sight the very same that we do now;
but unto those visible appearances there would not be connected those
different tangible magnitudes that are now. Which shews the judgments we
make of the magnitude of things placed at a distance, from the various
greatness of the immediate objects of sight, do not arise from any
essential or necessary, but only a customary, tie which has been observed
betwixt them.
63. Moreover, it is not only certain that any idea of sight might not have
been connected with this or that idea of touch we now observe to accompany
it, but also that the greater visible magnitudes might have been connected
with and introduced into our minds lesser tangible magnitudes, and the
lesser visible magnitudes greater tangible magnitudes. Nay, that it
actually is so, we have daily experience—that object which makes a strong
and large appearance not seeming near so great as another the visible
magnitude whereof is much less, but more faint,(353) and the appearance
upper, or which is the same thing, painted lower on the retina, which
faintness and situation suggest both greater magnitude and greater
distance.
64. From which, and from sect. 57 and 58, it is manifest that, as we do
not perceive the magnitude of objects immediately by sight, so neither do
we perceive them by the mediation of anything which has a necessary
connexion with them. Those ideas that now suggest unto us the various
magnitudes of external objects before we touch them might possibly have
suggested no such thing; or they might have signified them in a direct
contrary manner, so that the very same ideas on the perception whereof we
judge an object to be small might as well have served to make us conclude
it great;—those ideas being in their own nature equally fitted to bring
into our minds the idea of small or great, or no size at all, of outward
objects(354), just as the words of any language are in their own nature
indifferent to signify this or that thing, or nothing at all.
65. As we see distance so we see magnitude. And we see both in the same
way that we see shame or anger in the looks of a man. Those passions are
themselves invisible; they are nevertheless let in by the eye along with
colours and alterations of countenance which are the immediate object of
vision, and which signify them for no other reason than barely because
they have been observed to accompany them. Without which experience we
should no more have taken blushing for a sign of shame than of gladness.
66. We are nevertheless exceedingly prone to imagine those things which
are perceived only by the mediation of others to be themselves the
immediate objects of sight, or at least to have in their own nature a
fitness to be suggested by them before ever they had been experienced to
coexist with them. From which prejudice every one perhaps will not find it
easy to emancipate himself, by any the clearest convictions of reason. And
there are some grounds to think that, if there was one only invariable and
universal language in the world, and that men were born with the faculty
of speaking it, it would be the opinion of some, that the ideas in other
men’s minds were properly perceived by the ear, or had at least a
necessary and inseparable tie with the sounds that were affixed to them.
All which seems to arise from want of a due application of our discerning
faculty, thereby to discriminate between the ideas that are in our
understandings, and consider them apart from each other; which would
preserve us from confounding those that are different, and make us see
what ideas do, and what do not, include or imply this or that other
idea(355).
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67. There is a celebrated phenomenon(356) the solution whereof I shall
attempt to give, by the principles that have been laid down, in reference
to the manner wherein we apprehend by sight the magnitude of objects.—The
apparent magnitude of the moon, when placed in the horizon, is much
greater than when it is in the meridian, though the angle under which the
diameter of the moon is seen be not observed greater in the former case
than in the latter; and the horizontal moon doth not constantly appear of
the same bigness, but at some times seemeth far greater than at others.
68. Now, in order to explain the reason of the moon’s appearing greater
than ordinary in the horizon, it must be observed that the particles which
compose our atmosphere do intercept the rays of light proceeding from any
object to the eye; and, by how much the greater is the portion of
atmosphere interjacent between the object and the eye, by so much the more
are the rays intercepted, and, by consequence, the appearance of the
object rendered more faint—every object appearing more vigorous or more
faint in proportion as it sendeth more or fewer rays into the eye. Now,
between the eye and the moon when situated in the horizon there lies a far
greater quantity of atmosphere than there does when the moon is in the
meridian. Whence it comes to pass, that the appearance of the horizontal
moon is fainter, and therefore, by sect. 56, it should be thought bigger
in that situation than in the meridian, or in any other elevation above
the horizon.
69. Farther, the air being variously impregnated, sometimes more and
sometimes less, with vapours and exhalations fitted to retund and
intercept the rays of light, it follows that the appearance of the
horizontal moon hath not always an equal faintness, and, by consequence,
that luminary, though in the very same situation, is at one time judged
greater than at another.
70. That we have here given the true account of the phenomena of the
horizontal moon, will, I suppose, be farther evident to any one from the
following considerations:—_First_, it is plain, that which in this case
suggests the idea of greater magnitude, must be something which is itself
perceived; for, that which is unperceived cannot suggest to our perception
any other thing(357). _Secondly_, it must be something that does not
constantly remain the same, but is subject to some change or variation;
since the appearance of the horizontal moon varies, being at one time
greater than at another. [_Thirdly_, it must not lie in the circumjacent
or intermediate objects, such as mountains, houses, fields, &c.; because
that when all those objects are excluded from sight the appearance is as
great as ever(358).] And yet, _thirdly_(359), it cannot be the visible
figure or magnitude; since that remains the same, or is rather lesser, by
how much the moon is nearer to the horizon. It remains therefore, that the
true cause is that affection or alteration of the visible appearance,
which proceeds from the greater paucity of rays arriving at the eye, and
which I term faintness: since this answers all the forementioned
conditions, and I am not conscious of any other perception that does.