which would be needless where the belief is as strong as that of
demonstration itself, is the paramount force of this universal and
irresistible belief; and there is no fear that this can be weakened by
any argument, or be less felt by him who denies it, than by him who
asserts it. We are conscious, indeed, only of the feelings that are the
momentary states of our own mind; but some of these it is absolutely
impossible for us not to ascribe to causes that are external, and
independent of us; and the belief of a system of external things, is
one of these very states of the mind, which itself forms, and will ever
form, a part of the train of our consciousness. This Mr Hume himself,
the great sceptic whom Dr Reid opposes, admits as readily as Dr Reid
himself:--“A Copernican or Ptolemaic, who supports each his different
system of astronomy, may hope to produce a conviction, which will
remain constant and durable, with his audience. A Stoic or Epicurean
displays principles, which may not only be durable, but which have
an effect on conduct and behaviour. But a Pyrrhonian cannot expect,
that his philosophy will have any constant influence on the mind:
or, if it had, that its influence would be beneficial to society. On
the contrary, he must acknowledge, if he will acknowledge any thing,
that all human life must perish, were his principles universally and
steadily to prevail. All discourse, all action, would immediately
cease; and men remain in a total lethargy, till the necessities of
nature, unsatisfied, put an end to their miserable existence. It is
true, so fatal an event is very little to be dreaded. Nature is always
too strong for principle; and, though a Pyrrhonian may throw himself,
or others, into a momentary amazement and confusion by his profound
reasonings, the first and most trivial event in life will put to flight
all his doubts and scruples, and leave him the same, in every point
of action and speculation, with the philosophers of every other sect,
or with those who never concerned themselves in any philosophical
researches. When he awakes from his dream, he will be the first to join
in the laugh against himself.”[113] In what respect does this differ
from the language of Dr Reid himself, when he says, that “the belief of
a material world is older, and of more authority, than any principles
of philosophy. It declines the tribunal of reason, and laughs at all
the artillery of the logician.”[114] Surely, if it decline the tribunal
of reason, it is not by reasoning that it is to be supported,--even
though the reasoner should have the great talents which Dr Reid
unquestionably possessed.
The sceptic, and the orthodox philosopher of Dr Reid's school,
thus come precisely to the same conclusion. The creed of each, on
this point, is composed of two propositions, and of the same two
propositions; the first of which is, that the existence of a system
of things, such as we understand when we speak of an external world,
cannot be proved by argument; and the second, that the belief of it
is of a force, which is paramount to that of argument, and absolutely
irresistible. The difference, and the only difference is, that, in
asserting the same two propositions, the sceptic pronounces the first
in a loud tone of voice, and the second in a whisper,--while his
supposed antagonist passes rapidly over the first, and dwells on the
second, with a tone of confidence. The negation in the one case, and
the affirmation in the other case, are, however, precisely the same.
To him, indeed, who considers the _tone_ only, and not the _meaning_,
there may seem to be a real strife of sentiment; but, if we neglect the
tone, which is of no consequence, and attend to the meaning only of
what is affirmed and denied by both, we shall not be able to discover
even the slightest discrepancy. There is no argument of mere reasoning
that can prove the existence of an external world; it is absolutely
impossible for us not to believe in the existence of an external world.
We may call these two propositions, then, a summary of the doctrine of
Reid, or of the doctrine of Hume, as we please; for it is truly the
common and equal doctrine of the two.
Though we have thus seen reason to deny to Dr Reid the merit commonly
ascribed to him, on the points which we have been considering, relative
to the theory of perception, I trust you will not on that account,
be insensible to the merits which he truly possessed. _He_ knows
little, indeed, of the human mind, who does not know, how compatible
many errors and misconceptions are with the brightest and most active
energies of intellect. On this “Isthmus of a middle State,” of which
Pope speaks, man, though not “reasoning but to err,” is yet subject to
occasional error, even in his proudest reasonings. With all his wisdom,
he is still but “darkly wise;” and with all the grandeur of his being,
but “rudely great.”
VISION.
Our inquiry into the nature of the sensations of _touch_,--or at
least of those sensations, which are truly, and of others which are
commonly, though, I think, falsely, ascribed to this organ, has led
us into speculations, in the course of which I have been obliged to
anticipate many remarks, that more peculiarly belong to the sense which
still remains to be considered by us,--the sense of sight, that to
which we owe so much of our most valuable information, with respect to
nature, and so many of those pleasures, which the bounty of Him, who,
has formed us to be happy, as well as to be wise, has so graciously
intermingled, with all the primary means of our instruction.
The anticipations, into which I have been led, were necessary for
throwing light on the subjects before considered, particularly on the
complex feelings ascribed to touch,--the knowledge of which feelings,
however, was still more necessary, for understanding fully the complex
perceptions of this sense. It is thus scarcely possible, in science,
to treat of _one_ subject, without considering it in relation to some
other subject, and often to subjects between which, on first view, it
would be difficult to trace any relation. Every thing throws light
upon every thing,--though the reflection,--which is, in many cases, so
bright, as to force itself upon common eyes--may, in other cases, be
so faint, as to be perceptible only to eyes of the nicest discernment.
It may almost be said, that there is an universal _affinity_ in
_truths_,--like that universal attraction, which unites to each other,
as one common system, the whole masses which are scattered through
the infinity of space, and by which, as I have before remarked, the
annihilation of a single particle of matter, in any one of these
orbs,--however inconceivably slight its elementary modification might
be of the general sum of attraction,--would in that very instant be
productive of change throughout the universe. It is not easy to say,
what any _one_ science would have been, if any other science had not
existed. How different did Astronomy become, in consequence of the
accidental burning of a few sea-weeds upon the sand, to which the
origin of glass has been ascribed; and, when we think of the universal
accessions, which navigation has made to every department of knowledge,
what an infinity of truths may be considered as almost starting into
existence, at the moment, when the polarity of the magnet was first
observed!
“True to the pole, by thee the pilot guides
His steady helm, amid the struggling tides,
Braves with broad sail the unmeasurable sea,
Cleaves the dark air, and asks no star but thee.”[115]
The anticipations, which have been made, in the present instance, will
be of advantage, in abridging much of the labour, which would have been
necessary in treating of vision simply. I may now safely leave you, to
make, for yourselves, the application of many arguments, on which I
have dwelt at length, in treating of the other senses.
The organ of sight, as you well know, is the eye,--a machine of such
exquisite and obvious adaptation to the effects produced by it, as to
be, of itself, in demonstrating the existence of the Divine Being who
contrived it, equal in force to many volumes of theology. The atheist,
who has seen, and studied, its internal structure, and yet _continues
an atheist_, may be fairly considered as beyond the power of mere
argument to reclaim. The minute details of its structure, however,
belong to the anatomist. It is enough for our purpose to know, that,
by an apparatus of great simplicity, all the light, which, from every
quarter strikes on the pellucid part of the ball of the eye,--and which
if it continued to pass in the same direction, would thus produce one
mingled and indistinct expanse of colour,--is so _refracted_, as it is
termed, or bent from its former direction to certain focal points, as
to be distributed again on the retina, in distinct portions, agreeing
with the portions which come from each separate object, so exactly, as
to form on it a miniature landscape of the scenery without. Nor is this
all. That we may vary, at our pleasure, the field of this landscape,
the ball of the eye is furnished with certain muscles, which enable
us to direct it more particularly toward the objects which we wish to
view; and according as the light which falls from these may be more
or less intense, there are parts which minister to the sensibility of
the eye, by increasing or diminishing in proportion the transparent
aperture at which the light is admitted. There are, then, in this truly
wonderful and beautiful process, in the first place, as determining
what objects, in the wide scene around us, are to be visible at the
moment, _the contraction of certain muscles_, on which the particular
field of our vision depends, and which may almost be said to enable us
to increase the extent of our field of vision, by enabling us to vary
it at will;--in the second place, the _external light_, emitted from
all the objects within this radiant field, which, on its arrival at
the retina, is itself the direct object of vision; in the third place,
the provision for increasing or diminishing the diameter of the pupil,
in proportion to the quantity of that incident light;--in the fourth
place, the _apparatus_, by which the dispersed rays of light are made
to assume within the eye, the focal convergence necessary for distinct
vision;--and lastly, the expansion of the optic nerve, as a part of
the great sensorial organ, essential to sensation. The difference
of the phenomena, produced by the varieties of the external light
itself, is exhibited in almost every moment of our waking existence;
and the diversities, arising from other parts of the process, are
not less striking. There are peculiar diseases which affect the optic
nerve, or other parts of the sensorial organ immediately connected
with it,--there are other diseases which affect the refracting
apparatus,--others which affect the iris, so as to prevent the
enlargement or diminution of the pupil, when different quantities of
light are poured on it,--others, which affect the muscles that vary the
position of the ball,--and, in all these cases, we find, as might be
expected, a corresponding difference of the phenomena.
To open our eyes at present, is not to have a single simple feeling;
it is, as it were, to have innumerable feelings. The colour, the
magnitude, the figure, the relative position of bodies, are seen by us
at once. It is not a small expanse of light, which we perceive, equal
merely to the surface of the narrow expansion of the optic nerve. It
is the universe itself. We are present with stars, which beam upon
us, at a distance that converts to nothing the whole wide diameter of
our planetary system. It is as if the tie, which binds us down to the
globe on which we dwell, belonged only to our other senses, and had no
influence over _this_, which, even in its union with the body, seems
still to retain all the power, and unbounded freedom, of its celestial
origin.
It is of importance, however, to remember, that, even in the perception
of the most distant body, the true object of vision is not the distant
body itself, but the light that has reached the expansive termination
of the optic nerve; and the sense of vision, therefore, which seems so
independent of the tie that binds us to our small spot of earth, is as
truly limited to it, as any of our other senses. If the light could
exist in the same manner, moving in the same varieties of direction,
as at present,--though no other bodies were in existence, than the
light itself, and our sensorial organ,--all the sensations belonging
to mere sight would be exactly the same as now; and accordingly we
find, as light is, in a great measure, manageable by us, that we have
it in our power to vary at pleasure, the visual notions, which any one
would otherwise have formed of bodies,--without altering the bodies
themselves, or even their position with respect to the eye,--by merely
interposing substances, to modify the light reflected or emitted from
them. The same paper, which we term white, when we observe it with our
naked eye, seems blue or red, when we look at it through glass, of
such a kind, as absorbs all the light which enters it, but the rays
of those particular colours; and it seems larger or smaller, as we
look at it through a concave or convex lens, which leaves the object
precisely as it was, and affects only the direction of the rays that
come from it:--the reason of all which diversities of perception is,
that, though what we are accustomed to term the _object_ continues
the same,--whatever substance may be interposed between it and the
eye,--that, which is really the object of vision, is _different_; and
our perceptions, therefore, correspond with the diversity of their real
objects.
In treating of the distinction which has been made, of those objects
of sense which act _directly_ on our organs, and of those which act
through a _medium_, as it has been termed, I before remarked to you
the confusion, into which we might be led, by this distinction, which
forgets that the supposed _medium_ is itself the real _object_, as
truly, as any of the objects, which in their relations to other
senses, are termed _direct_. In no instance, however, has it led to so
much confusion, as in the case of vision. It is the more important,
therefore, for you, to have precise notions on this subject, and to
have constantly in mind, that, though indirectly, we may be said to
perceive by sight distant objects, as truly as we perceive colour,
still the _direct_ object of _vision_ is not the object, existing
permanently at a distance, but those rays of light, whose existence is
independent of the object, and which have received, from the object
that reflects them, nothing more than a change of their direction,
in consequence of which they have come within the boundary of that
small pellucid circle of the eye, which, insignificant as it may seem,
comprehends in itself what is truly the whole sphere of our vision.
_Sight_, then, which comprehends all the varieties of colour, is the
object, and the only object, of the sense which we are considering.
But, simple as it is, of what instruction, and joy, and beauty, and
ever-varying magnificence, is it the source!
“Carmine quo Dea te dicam, gratissima coeli
Progenies, ortumque tuum; gemmantia rore
Ut per prata levi lustras, et floribus halans
Purpureum Veris gremium, scenamque virentem
Pingis, et umbriferos colles, et cærula regna?
Gratia te Venerisque lepos, et mille colorum,
Formarumque chorus sequitur, motusque decentes.
At caput invisum Stygiis Nox atra tenebris.
Abdidit, horrendæque simul Formidinis ora
Pervigilesque æstus Curarum, atque anxius Angor;
Undique Lætitiâ florent mortalia corda,
Purus et arridet largis fulgoribus Æther.”[116]
“Hail, holy light, offspring of heaven first born!
Or of the Eternal, coeternal beam,
May I express thee unblam'd? since God is light,
And never but in unapproached light
Dwelt from eternity; dwelt then in Thee,
Bright Effluence of bright Essence increate!
--Or hear'st thou rather, pure ethereal Stream!
Whose fountain who shall tell? Before the Sun,
Before the heavens, _Thou_ wert, and at the voice
Of God, as with a mantle didst invest
The rising world of waters dark and deep,
Won from the void and formless infinite.”[117]
How pathetic is the very beauty of this invocation, when we consider
the feelings with which it must have been written by him, who,
“Like the wakeful bird,
Sung _darkling_,”[118]
and who seems to have looked back on that loveliness of nature, from
which he was separated, with the melancholy readiness, with which the
thoughts of the unfortunate and the sorrowful still revert to past
enjoyments; as the prisoner, even when fettered to his dungeon-floor,
still turns his eye, almost involuntarily, to that single gleam of
light, which reminds him only of scenes that exist no longer to him.
“Thus with the year
Seasons return; but _not_ to _me_ returns
Day, or the sweet approach of even or morn,
Or sight of vernal bloom, or summer's rose,
Or flocks, or herds, or human face divine;
But cloud instead, and ever-during dark
Surround me.”[119]
How often must he have felt,--and how deeply must such a mind have
felt,--the force of that complaint, which he puts into the mouth of
Samson,--a complaint, which may surely be forgiven, or almost forgiven,
to the blind:--
“O why was sight
To such a tender ball as the eye confined,
So obvious, and so easy to be quench'd;
And not, as feeling, through all parts diffused,
That she might look at will through every pore?”[120]
The immediate object of vision, we have seen, then, is _light_, which
gives rise to all the various sensations of colour; and, since the days
of Berkeley, philosophers have, with scarcely any exception, admitted,
that the knowledge of the distance, magnitude, and real figure of
objects, which seems at present to be immediately received by sight,
is the result of knowledge acquired by the other senses:--though they
have,--I think without sufficient reason,--as universally supposed,
that the superficial extension, of length and breadth, becomes known to
us by sight originally;--that there is, in short, a _visible figure_ of
objects, corresponding with the picture which they form on the retina,
and changing, therefore, with their change of position relatively to
the eye,--and a _tangible figure_ of objects, permanent and independent
of their change of place; the latter being the real figure suggested by
the former, nearly in the same manner as the conception of objects is
suggested, by the arbitrary sounds, or written character, which denote
them. The inquiry, with respect to the truth of this visible figure,
as a sensation, may, however, be omitted, till we have considered the
former opinion, which respects the visual perception of distance, and
of the figure and magnitude which are termed _tangible_.
If it had been duly considered, that it is _light_ which is the true
object of vision, and not the luminous body, the question, as far as
it depends on reasoning _a priori_, exclusively of any instinctive
connexions that might be supposed, could not have admitted of very
long discussion. From whatever distance light may come, it is but the
_point_ of the long line which terminates at the retina, of which we
are sensible; and this terminating point must be the same, whether the
ray has come from a few feet of distance, or from many miles. The rays,
that beam from the adjacent meadow, or the grove, are not nearer to my
eye, at the instant of vision, than those which have been reflected
from the mountain, on the very verge of the horizon, or from the cloud
that hangs at an immeasurable distance above my head. The light, that
converges on our eye, from all the stars of heaven, within what we
term the field of our vision, is collected, in a space, that cannot
be larger than the retina on which it falls. A _cube_ or a _sphere_
is represented to us, by the two dimensions of a coloured _plane_,
variously shaded, as truly, as by the object itself with its triple
dimensions; and, in the determination of the exact correspondence
of these double and triple dimensions, in all their varieties of
relation to the eye, the whole art of perspective consists. A coin of
a single inch in diameter, when placed before the eye, and, of course,
intercepting only an extent of light equal to the extent of its own
surface, is sufficient to hide from us, by actual eclipse, the fields,
and villages, and woods, that seemed stretched in almost endless
continuity before us.
Unless, therefore, there be some instinctive and immediate suggestion,
of certain distances, magnitudes, and figures, by certain varieties of
the sensation of colour, there is nothing in the mere light itself, or
in its relation to the eye at the moment of vision, which seems fit to
communicate the knowledge of these. Not of _distance_; for the rays
from distant objects, when they produce vision, are as near to the
retina, as the rays from objects that are contiguous to the eye. Not of
_real magnitude_; for an object, with which we are familiar, appears to
us of the same size, at distances, at which every thing merely visual
is so completely changed, that its magnitude, as far as it depends on
mere radiation, may be demonstrated, from the laws of optics, to be
equal only to a half, or a tenth part of its apparent magnitude, when
nearer. Not of _figure_; for, without the knowledge of longitudinal
distance, we could not distinguish a sphere or a cube from a plane
surface of two dimensions; and an object, with the shape of which we
are familiar, appears to us of the same form, in all directions; though
it may be demonstrated optically, that the visual figure, as far as it
depends on mere radiation, must vary with every variety of position.
I have said, that the knowledge of the real magnitude, figure, and
position of bodies, could not be obtained immediately from the
diversities of the mere surfaces of light at the retina; unless it
were the suggestion of some instinctive principle, by which the one
feeling was, originally and inseparably, connected with the other: and
I have made this exception, to prevent you from being misled, by the
works on this subject, so as to think, that the original perception of
distance implies, in the very notion of it, a physical impossibility.
Some diversity there evidently must be of the immediate sensation of
sight, or of other feelings coexisting with it, when a difference
of magnitude or figure is suggested: the visual affection, which is
followed by the notion of a mile, cannot be the same as that which is
attended with the notion of half a foot; nor that which is attended
with the perception of a sphere, be the same as that which suggests a
plane circular surface. Whatever the number of the varied suggestions
of this kind may be, there must be, at least, an equal variety of the
immediate sensations that give rise to them; and these corresponding
series of sensations and suggestions, may originally be associated
together by an instinctive principle, as much as any other pairs of
phenomena, the connexion of which we ascribe to instinct; or, in other
words, suppose an adaptation of them to each other, by the gracious
provision of the Power which formed us, for a purpose unforeseen by
us, and unwilled at the moment. It is not more wonderful, _a priori_,
that a sensation of colour should be immediately followed by the notion
of a mile of distance, than that the irritation of the nostril, by
any very stimulant odour, should be immediately and involuntarily,
followed by the sudden contraction of a distant muscular organ, like
the diaphragm, which produces, in sneezing, the violent expiration
necessary for expelling the acrid matter;--or that an increase of the
quantity of light poured on the eye, should be instantly, and without
our consciousness, followed by a contraction of the transparent
aperture. I am far from saying, that there truly is such an instinctive
association of our original visual feelings, with corresponding notions
of distance and magnitude, in the present case; for, at least in
_man_, I believe the contrary. I mean only, that the question has, _a
priori_, only greater probability on one side, not absolute certainty;
and that experience is necessary, before we can decide it with perfect
confidence.
In the case of the other animals, there seems to be little reason
to doubt, that the tedious process, by which man may be truly said
to learn to see, is not necessary for their visual perceptions. The
calf, and the lamb, newly dropt into the world, seem to measure forms
and distances with their eyes, as distinctly, or at least almost
as distinctly, as the human reasoner measures them, after all the
acquisitions of his long and helpless infancy. Of these races of
our fellow animals, Nature is as once the _Teacher_ and the great
_Protectress_,--supplying to them, immediately, the powers which are
necessary for their preservation,--as, in the long continued affection
of the human parent, she far more than compensates to man, the early
instincts which she has denied to him. If the other animals had to
learn to see, in the same manner with ourselves, it would be scarcely
possible, that their existence should be preserved to the period,
at which the acquisitions necessary for accurate perception could
be made; even though the hoof had been an instrument of touch and
measurement, as convenient as the hand. For this difference in the
relative circumstances of their situation, the Almighty Being,--to
whose universal benevolence, nothing which he has created is too humble
for his care,--has made sufficient provision, in giving them that early
maturity, which makes them, for many months, the _superiors_ of him,
who is afterwards to rule them with a sway, that is scarcely conscious
of effort.