acknowledged that we never see and feel one and the same object. 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. 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.
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; they may indeed
grow greater or smaller, more confused, or more clear, or more faint, but
they do not, cannot approach 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, 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. 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 reflexion. However, I believe 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.
52. I have now done with distance, and proceed to show how it is that we
perceive by sight the magnitude of objects. 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, and the things we
see being in truth at no distance from us, it follows that as we have
shown 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, 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 hath been already said, and what
follows.
54. It hath been shown there are two sorts of objects apprehended by
sight; each whereof hath 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, it is certain sensible
extension is not infinitely divisible. There is a MINIMUM TANGIBILE and a
MINIMUM VISIBILE, beyond which sense cannot perceive. This everyone'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 anything, 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. But though the tangible and visible
magnitude in truth belong to two distinct objects: I shall nevertheless
(especially since those objects are called by the same name, and are
observed to coexist), 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. CETERIS 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 hath 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 of 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 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, 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
sensation of pleasure or pain. Now bodies operating on our organs, by an
immediate application, and the hurt or 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 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 any
wise altering the frame of their bodies) they may be able to foresee
(from the experience they have had what tangible ideas are connected with
such and such visible ideas) and 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, everyone'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 concern us, and are not fitted to produce any
alteration in our bodies.
60. That the matter of fact is true will be evident to anyone who
considers that a man placed at ten foot distance is thought as great as
if he were placed at a 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, etc., 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, etc., is evident, because a visible inch is itself no
constant, determinate magnitude, 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, etc., 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 to
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, 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 shows 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 between 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, which 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, 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 magnitudes 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; 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 exceeding 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 everyone, perhaps, will not find it easy
to emancipate himself, by any [but] the clearest convictions of reason.
And there are some grounds to think that if there was one only invariable
and universal languages in the world, and that men were born with the
faculty of speaking it, it would be the opinion of many that the ideas of
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.
67. There is a celebrated phenomenon, 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 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 anyone 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. 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. And yet, THIRDLY, 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 doth.
71. Add to this that in misty weather it is a common observation that the
appearance of the horizontal moon is far larger than usual, which greatly
conspires with and strengthens our opinion. Neither would it prove in the
least irreconcilable with what we have said, if the horizontal moon
should chance sometimes to seem enlarged beyond its usual extent, even in
more serene weather. For we must not only have regard to the mist which
happens to be in the place where we stand; we ought also to take into our
thoughts the whole sum of vapours and exhalations which lie betwixt the
eye and the moon: all which cooperating to render the appearance of the
moon more faint, and thereby increase its magnitude, it may chance to
appear greater than it usually does, even in the horizontal position, at
a time when, though there be no extraordinary fog or haziness, just in
the place where we stand, yet the air between the eye and the moon, taken
all together, may be loaded with a greater quantity of interspersed
vapours and exhalations than at other times.
72. It may be objected that in consequence of our principles the
interposition of a body in some degree opaque, which may intercept a
great part of the rays of light, should render the appearance of the moon
in the meridian as large as when it is viewed in the horizon. To which I
answer, it is not faintness anyhow applied that suggests greater
magnitude, there being no necessary but only an experimental connexion
between those two things. It follows that the faintness which enlarges
the appearance must be applied in such sort, and with such circumstances,
as have been observed to attend the vision of great magnitudes. When from
a distance we behold great objects, the particles of the intermediate air
and vapours, which are themselves unperceivable, do interrupt the rays of
light, and thereby render the appearance less strong and vivid: now,
faintness of appearance caused in this sort hath been experienced to
coexist with great magnitude. But when it is caused by the interposition
of an opaque sensible body, this circumstance alters the case, so that a
faint appearance this way caused doth not suggest greater magnitude,
because it hath not been experienced to coexist with it.