The painter seeks to produce in his picture an image of external
objects. The first aim of our investigation must be to ascertain what
degree and what kind of similarity he can expect to attain, and what
limits are assigned to him by the nature of his method. The uneducated
observer usually requires nothing more than an illusive resemblance
to nature: the more this is obtained, the more does he delight in the
picture. An observer, on the contrary, whose taste in works of art has
been more finely educated, will, consciously or unconsciously, require
something more, and something different. A faithful copy of crude
Nature he will at most regard as an artistic feat. To satisfy him, he
will need artistic selection, grouping, and even idealisation of the
objects represented. The human figures in a work of art must not be
the everyday figures, such as we see in photographs; they must have
expression, and a characteristic development, and if possible beautiful
forms, which have perhaps belonged to no living individuals or indeed
any individuals which ever have existed, but only to such a one as
might exist, and as must exist, to produce a vivid perception of any
particular aspect of human existence in its complete and unhindered
development.
If however the artist is to produce an artistic arrangement of only
idealised types, whether of man or of natural objects, must not the
picture be an actual, complete, and directly true delineation of that
which would appear if it anywhere came into being?
Since the picture is on a plane surface, this faithful representation
can of course only give a faithful perspective view of the objects.
Yet our eye, which in its optical properties is equivalent to a camera
obscura, the well-known apparatus of the photographer, gives on the
retina, which is its sensitive plate, only perspective views of the
external world; these are stationary, like the drawing on a picture, as
long as the standpoint of the eye is not altered. And, in fact, if we
restrict ourselves in the first place to the form of the object viewed,
and disregard for the present any consideration of colour, by a correct
perspective drawing we can present to the eye of an observer, who views
it from a correctly chosen point of view, the same forms of the visual
image as the inspection of the objects themselves would present to the
same eye, when viewed from the corresponding point of view.
But apart from the fact that any movement of the observer, whereby his
eye changes its position, will produce displacements of the visual
image, different when he stands before objects from those when he
stands before the image, I could speak of only _one_ eye for which
equality of impression is to be established. We however see the world
with _two_ eyes, which occupy somewhat different positions in space,
and which therefore show two different perspective views of objects
before us. This difference of the images of the two eyes forms one of
the most important means of estimating the distance of objects from
our eye, and of estimating depth, and this is what is wanting to the
painter, or even turns against him; since in binocular vision the
picture distinctly forces itself on our perception as a plane surface.
You must all have observed the wonderful vividness which the solid
form of objects acquires when good stereoscopic images are viewed in
the stereoscope, a kind of vividness in which either of the pictures
is wanting when viewed without the stereoscope. The illusion is most
striking and instructive with figures in simple line; models of
crystals and the like, in which there is no other element of illusion.
The reason of this deception is, that looking with two eyes we view
the world simultaneously from somewhat different points of view, and
thereby acquire two different perspective images. With the right eye
we see somewhat more of the right side of objects before us, and also
somewhat more of those behind it, than we do with the left eye; and
conversely we see with the left, more of the left side of an object,
and of the background behind its left edges, and partially concealed
by the edge. But a flat picture shows to the right eye absolutely the
same picture, and all objects represented upon it, as to the left eye.
If then we make for each eye such a picture as that eye would perceive
if itself looked at the object, and if both pictures are combined in
the stereoscope, so that each eye sees its corresponding picture, then
as far as form is concerned the same impression is produced in the
two eyes as the object itself produces. But if we look at a drawing
or a picture with both eyes, we just as easily recognise that it is a
representation on a plane surface, which is different from that which
the actual object would show simultaneously to both eyes. Hence is due
the well-known increase in the vividness of a picture if it is looked
at with only one eye, and while quite stationary, through a dark tube;
we thus exclude any comparison of its distance with that of adjacent
objects in the room. For it must be observed that as we use different
pictures seen with the two eyes for the perception of depth, in like
manner as the body moves from one place to another, the pictures seen
by the same eye serve for the same purpose. In moving, whether on foot
or riding, the nearer objects are apparently displaced in comparison
with the more distant ones; the former appear to recede, the latter
appear to move with us. Hence arises a far stricter distinction between
what is near and what is distant, than seeing with one eye from one and
the same spot would ever afford us. If we move towards the picture, the
sensuous impression that it is a flat picture hanging against the wall
forces itself more strongly upon us than if we look at it while we are
stationary. Compared with a large picture at a greater distance, all
those elements which depend on binocular vision and on the movement
of the body are less operative, because in very distant objects the
differences between the images of the two eyes, or between the aspect
from adjacent points of view, seem less. Hence large pictures furnish
a less distorted aspect of their object than small ones, while the
impression on a stationary eye, of a small picture close at hand, might
be just the same as that of a large distant one. In a painting close at
hand, the fact that it is a flat picture continually forces itself more
powerfully and more distinctly on our perception.
The fact that perspective drawings, which are taken from too near a
point of view, may easily produce a distorted impression, is, I think,
connected with this. For here the want of the second representation
for the other eye, which would be very different, is too marked. On
the other hand, what are called geometrical projections, that is,
perspective drawings which represent a view taken from an infinite
distance, give in many cases a particularly favourable view of the
object, although they correspond to a point of sight which does not in
reality occur. Here the pictures of both eyes for such an object are
the same.
You will notice that in these respects there is a primary incongruity,
and one which cannot be got over, between the aspect of a picture and
the aspect of reality. This incongruity may be lessened, but never
entirely overcome. Owing to the imperfect action of binocular vision,
the most important natural means is lost of enabling the observer
to estimate the depth of objects represented in the picture. The
painter possesses a series of subordinate means, partly of limited
applicability, and partly of slight effect, of expressing various
distances by depth. It is not unimportant to become acquainted with
these elements, as arising out of theoretical considerations; for in
the practice of the art of painting they have manifestly exercised
great influence on the arrangement, selection, and mode of illumination
of the objects represented. The distinctness of what is represented is
indeed of subordinate importance when considered in reference to the
ideal aims of art; it must not however be depreciated, for it is the
first condition by which the observer attains an intelligibility of
expression, which impresses itself without fatigue on the observer.
This direct intelligibility is again the preliminary condition for an
undisturbed, and vivid action of the picture on the feelings and mood
of the observer.
The subordinate methods of expressing depth which have been referred
to, depend in the first place on perspective. Nearer objects partially
conceal more distant ones, but can never themselves be concealed by
the latter. If therefore the painter skilfully groups his objects, so
that the feature in question comes into play, this gives at once a very
certain gradation of far and near. This mutual concealment may even
preponderate over the binocular perception of depth, if stereoscopic
pictures are intentionally produced in which each counteracts the
other. Moreover, in bodies of regular or of known form, the forms of
perspective projection are for the most part characteristic for the
depth of the object. If we look at houses, or other results of man’s
artistic activity, we know at the outset that the forms are for the
most part plane surfaces at right angles to each other, with occasional
circular or even spheroidal surfaces. And in fact, when we know so
much, a correct perspective drawing is sufficient to produce the whole
shape of the body. This is also the case with the figures of men and
animals which are familiar to us, and whose forms moreover show two
symmetrical halves. The best perspective drawing is however of but
little avail in the case of irregular shapes, rough blocks of rock and
ice, masses of foliage, and the like; that this is so, is best seen
in photographs, where the perspective and shading may be absolutely
correct, and yet the total impression is indistinct and confused.
When human habitations are seen in a picture, they represent to the
observer the direction of the horizontal surfaces at the place at which
they stand; and in comparison therewith the inclination of the ground,
which without them would often be difficult to represent.
The apparent magnitude which objects, whose actual magnitude is known,
present in different parts of the picture must also be taken into
account. Men and animals, as well as familiar trees, are useful to the
painter in this respect. In the more distant centre of the landscape
they appear smaller than in the foreground, and thus their apparent
magnitude furnishes a measure of the distance at which they are placed.
Shadows, and more especially double ones, are of great importance. You
all know how much more distinct is the impression which a well-shaded
drawing gives as distinguished from an outline; the shading is hence
one of the most difficult, but at the same time most effective,
elements in the productions of the draughtsman and painter. It is his
task to imitate the fine gradation and transitions of light and shade
on rounded surfaces, which are his chief means of expressing their
modelling, with all their fine changes of curvature; he must take
into account the extension or restriction of the sources of light,
and the mutual reflection of the surfaces on each other. While the
modifications of the lighting on the surface of bodies themselves
is often dubious--for instance, an intaglio of a medal may, with a
particular illumination, produce the impression of reliefs which are
only illuminated from the other side--double shadows, on the contrary,
are undoubted indications that the body which throws the shadow is
nearer the source of light than that which receives the shadow. This
rule is so completely without exception, that even in stereoscopic
views a falsely placed double shadow may destroy or confuse the entire
illusion.
The various kinds of illumination are not all equally favourable for
obtaining the full effect of shadows. When the observer looks at the
objects in the same direction as that in which light falls upon them,
he sees only their illuminated sides and nothing of the shadow; the
whole relief which the shadows could give then disappears. If the
object is between the source of light and the observer he only sees the
shadows. Hence we need lateral illumination for a picturesque shading;
and over surfaces which like those of plane or hilly land only present
slightly moving figures, we require light which is almost in the
direction of the surface itself, for only such a one gives shadows.
This is one of the reasons which makes illumination by the rising or
the setting sun so effective. The forms of the landscape become more
distinct. To this must also be added the influence of colour, and of
aerial light, which we shall subsequently discuss.
Direct illumination from the sun, or from a flame, makes the shadows
sharply defined, and hard. Illumination from a very wide luminous
surface, such as a cloudy sky, makes them confused, or destroys
them altogether. Between these two extremes there are transitions;
illumination by a portion of the sky, defined by a window, or by trees,
&c., allows the shadows to be more or less prominent according to the
nature of the object. You must have seen of what importance this is to
photographers, who have to modify their light by all manner of screens
and curtains in order to obtain well-modelled portraits.
Of more importance for the representation of depth than the elements
hitherto enumerated, and which are more or less of local and accidental
significance, is what is called _aerial perspective_. By this we
understand the optical action of the light, which the illuminated
masses of air, between the observer and distant objects, give. This
arises from a fine opacity in the atmosphere, which never entirely
disappears. If, in a transparent medium, there are fine transparent
particles of varying density and varying refrangibility, in so far as
they are struck by it, they deflect the light passing through such
a medium, partly by reflection and partly by refraction; to use an
optical expression, they _scatter_ it in all directions. If the opaque
particles are sparsely distributed, so that a great part of the light
can pass through them without being deflected, distant objects are
seen in sharp, well-defined outlines through such a medium, while at
the same time a portion of the light which is deflected is distributed
in the transparent medium as an opaque halo. Water rendered turbid by
a few drops of milk shows this dispersion of the light and cloudiness
very distinctly. The light in this case is deflected by the microscopic
globules of butter which are suspended in the milk.
In the ordinary air of our rooms, this turbidity is very apparent when
the room is closed, and a ray of sunlight is admitted through a narrow
aperture. We see then some of these solar particles, large enough to be
distinguished by the naked eye, while others form a fine homogeneous
turbidity. But even the latter must consist mainly of suspended
particles of organic substances, for, according to an observation of
Tyndall, they can be burnt. If the flame of a spirit lamp is placed
directly below the path of these rays, the air rising from the flame
stands out quite dark in the surrounding bright turbidity; that is to
say, the air rising from the flame has been quite freed from dust.
In the open air, besides dust and occasional smoke, we must often
also take into account the turbidity arising from incipient aqueous
deposits, where the temperature of moist air sinks so far that the
water retained in it can no longer exist as invisible vapour. Part of
the water settles then in the form of fine drops, as a kind of the very
finest aqueous dust, and forms a finer or denser fog; that is to say,
cloud. The turbidity which forms in hot sunshine and dry air may arise,
partly from dust which the ascending currents of warm air whirl about;
and partly from the irregular mixture of cold and warm layers of air
of different density, as is seen in the tremulous motion of the lower
layers of air over surfaces irradiated by the sun. But science can as
yet give no explanation of the turbidity in the higher regions of the
atmosphere which produces the blue of the sky; we do not know whether
it arises from suspended particles of foreign substances, or whether
the molecules of air themselves may not act as turbid particles in the
luminous ether.
The colour of the light reflected by the opaque particles mainly
depends on their magnitude. When a block of wood floats on water, and
by a succession of falling drops we produce small wave-rings near
it, these are repelled by the floating wood as if it were a solid
wall. But in the long waves of the sea, a block of wood would be
rocked about without the waves being thereby materially disturbed in
their progress. Now light is well known to be an undulatory motion
of the ether which fills all space. The red and yellow rays have the
longest waves, the blue and violet the shortest. Very fine particles,
therefore, which disturb the uniformity of the ether, will accordingly
reflect the latter rays more markedly than the red and yellow rays. The
light of turbid media is bluer, the finer are the opaque particles;
while the larger particles of uniform light reflect all colours, and
therefore give a whitish turbidity. Of this kind is the celestial
blue, that is, the colour of the turbid atmosphere as seen against
dark cosmical space. The purer and the more transparent the air, the
bluer is the sky. In like manner it is bluer and darker when we ascend
high mountains, partly because the air at great heights is freer
from turbidity, and partly because there is less air above us. But
the same blue, which is seen against the dark celestial space, also
occurs against dark terrestrial objects; for instance, when a thick
layer of illuminated air is between us and masses of deeply shaded or
wooded hills. The same aerial light makes the sky blue, as well as the
mountains; excepting that in the former case it is pure, while in the
latter it is mixed with the light from objects behind; and moreover
it belongs to the coarser turbidity of the lower regions of the
atmosphere, so that it is whiter. In hot countries, and with dry air,
the aerial turbidity is also finer in the lower regions of the air,
and therefore the blue in front of distant terrestrial objects is more
like that of the sky. The clearness and the pure colours of Italian
landscapes depend mainly on this fact. On high mountains, particularly
in the morning, the aerial turbidity is often so slight that the
colours of the most distant objects can scarcely be distinguished from
those of the nearest. The sky may then appear almost bluish-black.
Conversely, the denser turbidity consists mainly of coarser particles,
and is therefore whitish. As a rule, this is the case in the lower
layers of air, and in states of weather in which the aqueous vapour in
the air is near its point of condensation.
On the other hand, the light which reaches the eye of the observer
after having passed through a long layer of air, has been robbed of
part of its violet and blue by scattered reflections; it therefore
appears yellowish to reddish-yellow or red, the former when the
turbidity is fine, the latter when it is coarse. Thus the sun and the
moon at their rising and setting, and also distant brightly illuminated
mountain-tops, especially snow-mountains, appear coloured.
These colourations are moreover not peculiar to the air, but occur
in all cases in which a transparent substance is made turbid by the
admixture of another transparent substance. We see it, as we have
observed, in diluted milk, and in water to which a few drops of eau de
Cologne have been added, whereby the ethereal oils and resins dissolved
by the latter, separate out and produce the turbidity. Excessively
fine blue clouds, bluer even than the air, may be produced, as Tyndall
has observed, when the sun’s light is allowed to exert its decomposing
action on the vapours of certain carbon compounds. Goethe called
attention to the universality of this phenomenon, and endeavoured to
base upon it his theory of colour.
By aerial perspective we understand the artistic representation of
aerial turbidity; for the greater or less predominance of the aerial
colour above the colour of the objects, shows their varying distance
very definitely; and landscapes more especially acquire the appearance
of depth. According to the weather, the turbidity of the air may be
greater or less, more white or more blue. Very clear air, as sometimes
met with after continued rain, makes the distant mountains appear small
and near; whereas, when the air contains more vapour, they appear large
and distant.
This latter is decidedly better for the landscape painter, and the high
transparent landscapes of mountainous regions, which so often lead the
Alpine climber to under-estimate the distance and the magnitude of the
mountain-tops before him, are also difficult to turn to account in a
picturesque manner. Views from the valleys, and from seas and plains
in which the aerial light is faintly but markedly developed, are far
better; not only do they allow the various distances and magnitudes of
what is seen to stand out, but they are on the other hand favourable to
the artistic unity of colouration.
Although aerial colour is most distinct in the greater depths of
landscape, it is not entirely wanting in front of the near objects of
a room. What is seen to be isolated and well defined, when sunlight
passes into a dark room through a hole in the shutter, is also not
quite wanting when the whole room is lighted. Here, also, the aerial
lighting must stand out against the background, and must somewhat
deaden the colours in comparison with those of nearer objects; and
these differences, also, although far more delicate than against the
background of a landscape, are important for the historical, genre, or
portrait painter; and when they are carefully observed and imitated,
they greatly heighten the distinctness of his representation.