CHAPTER VI.

Light and its phenomena--Magic pictures--The optical
paradox--Chinese metallic mirrors--Effect of an optical
instrument on a superstitious mind--Origin of photography--The
Talbotype--The Daguerreotype--Sunlight pictures.


The cause of those sensations which we refer to the eyes, or that which
produces the sense of seeing, is light. The phenomena of vision have
always been regarded as among the most interesting branches of natural
science. The knowledge of the laws which regulate the phenomena of
light, constitutes the science of optics, which explains the cause of
many most striking illusions.

Magic pictures have been produced, which, when seen in a certain point
through a glass, exhibit an object different from that be held by the
naked eye. Niceron tells us that he executed at Paris, and deposited in
the library of the Minimes of the Place Royale, a picture of this kind;
when seen by the naked eye, it represented fifteen portraits of Turkish
sultans, but, when viewed through the glass, it was a portrait of Louis
XIII.

The writer has often seen a singular transformation effected by an
ingenious device, called the optical paradox: thus an eagle may be
changed into a lion, and a dog into a cat.

[Illustration]

[Illustration]

For this purpose, a wooden three-sided box must be prepared, and
through the open part may slide the various drawings to be used, as B.
Connected with this, there must be a pillar, C, and a horizontal bar
holding a tube, D, having in it a glass placed exactly over the centre.
The change is partly dependent on the glass, the sides of which are
flat and diverge from its hexagonal base upwards, to a point in the
axis of the glass, like a pyramid, E, forming an isosceles triangle.
All that is now necessary to the completion of the change, is in the
border of the drawing, in which the various parts required for the new
figure are cleverly introduced; so that when the distance of the glass
from the eye is rightly adjusted, each angular side will take up its
portion from the border, and present to the eye the various parts in an
entire figure. The shape of the glass prevents the appearance of any
particular figure in the centre, as the eagle, for instance; while the
lion, arranged in portions and drawn on the circle of refraction at six
different parts of the border, yet artfully disguised by blending with
it, the transformation will be completely produced.

A paper has lately been read to the Academy of Sciences at Paris, by M.
Stanislaus Julien, on the metallic mirrors made in China, and to which
the name of “magic mirrors” has been given. Hitherto all attempts by
Europeans to obtain information as to the process, in the localities
where they are manufactured, have proved failures, some of the persons
applied to being unwilling to reveal the secret, and others being
ignorant of the process. These mirrors are called magical, because,
if they receive the rays of the sun on their polished surface, the
characters, or flowers _in relief_, which exist on the other side, are
faithfully reproduced. The following information has been obtained
by M. Julien, from the writings of an author named Ou-tseu-hing, who
lived between 1260 and 1341:--“The cause of this phenomenon is the
distinct use of fine copper and rough copper. If, on the under side,
there be produced, by casting in a mould, the figure of a dragon in
a circle, there is then engraved deeply on the disc a dragon exactly
similar. Then, the parts which have been cut are filled with rather
rough copper; and this is, by the action of fire, incorporated with
the other metal, which is of a finer nature. The face of the mirror
is next prepared, and a slight coating of tin is spread over it. If
the polished disc of a mirror so prepared be turned towards the sun,
and the image be reflected on a wall, it presents distinctly the clear
portion and the dark portion, the one of the fine, and the other of the
rough copper.” Ou-tseu-hing states, that he had ascertained this by a
careful inspection of the fragments of a broken mirror.

It is easy for an ignorant and superstitious mind to confound a very
harmless and simple instrument with one of magical power. We have an
example of this in Dodwell’s description of his residence at Athens.
On his first admission within the venerable walls of the Acropolis,
it was necessary to offer a small present to the disdar, or Turkish
governor, and an additional sum to make drawings and observations
without being molested by the servants of the garrison. The disdar
proved to be a man of bad faith and insatiable rapacity, and, after
experiencing numerous vexations from the mercenary Turk, Dodwell was
at length released from his importunities by a singular circumstance.
As he was one day engaged in drawing the Parthenon, with the aid of
his camera obscura, the disdar, whose surprise was excited by the
novelty of the sight, asked, with a sort of fretful inquietude, what
new conjuration he was performing with that extraordinary machine.
Dodwell endeavoured to explain it, by putting in a clean sheet of
paper, and making him look at the instrument; but he no sooner saw the
Temple of Minerva reflected on the paper in all its lines and colours,
than he imagined the effect was produced by some magical process; his
astonishment appeared mingled with alarm, and, stroking his long black
beard, he repeated several times the words Allah, Masch-Allah--a term
of admiration with the Turks, signifying that which is made by God.

Again he looked into the camera obscura, with a kind of cautious
diffidence, and, at that moment, some of his soldiers happening to
pass before the reflecting-glass, were beheld by the astonished disdar
walking upon the paper. He now became outrageous; he assailed Dodwell
with various opprobrious epithets, one of which was Bonaparte--the
appellation being at the time synonymous to that of magician, or of
any one supposed to be endowed with supernatural talents--and declared
that, if Dodwell chose, he might take away all the stones in the
temple, but that he would not permit his soldiers to be conjured into
a box. “When I found,” says Dodwell, “that it was no use to reason
with his ignorance, I changed my tone, and told him that, if he did
not leave me unmolested, I would put him into my box; and that he
should find it a very difficult matter to get out again. His alarm was
now visible; he immediately retired, and ever after stared at me with
a mixture of apprehension and amazement. When he saw me come to the
Acropolis, he carefully avoided my approach; and never afterwards gave
me any further molestation.”

[Illustration]

The portable camera obscura, represented by the diagram, has often
yielded much pleasure in the domestic circle, while the larger ones,
which are publicly exhibited, are highly interesting. No person,
perhaps, has witnessed the neatness of outline, the precision of
form, the truth of colouring, and the sweet gradations of tint, thus
apparent, without regretting that an imagery so exquisite and faithful
to nature could not be made to fix itself permanently on the tablet of
the machine. Yet, in the estimation of all, such a wish seemed destined
to take its place among other dreams of beautiful things; the splendid
but impracticable conceptions in which men of science and ardent
temperament have sometimes indulged. Such a dream, however, has been
realized of late.

[Illustration]

Mr. Thomas Wedgewood, the celebrated porcelain manufacturer, so early
as 1802, published, in the journals of the Royal Institution, a
method of copying paintings upon glass, and of making profiles by the
agency of light upon nitrate of silver. The experiments he made were
repeated by sir Humphry Davy; but several years after, MM. Niepcé
and Daguerre, and Mr. Fox Talbot, laid the foundation of the present
state of photographic drawing. The former engaged in a long series of
experiments to render metallic surfaces peculiarly sensitive; the aim
of the latter was to produce this effect on paper. The camera obscura
used for this purpose is a rectangular box, with a double convex lens,
A, at one end, and a glass reflector, B, which is generally a piece
of looking-glass, at the other. Now, supposing the rays of light to
proceed from an extensive landscape, and pass through this small convex
lens, as we well know they may do, what will be the effect produced?
The scene will, in the first place, be thrown on the reflector, which
is fixed at an angle of forty-five degrees to the horizon. Now it
follows, from a law well known to opticians, that these rays will
be reflected to the top of the box, immediately over the mirror; so
that if a ground glass, or any other medium capable of receiving the
reflected image, be placed there, a representation of the landscape
may be observed. As then, it is proved, by innumerable experiments,
that reflected light has, in proportion to its power, as much influence
on prepared or photographic paper, as the direct rays of the sun; it
follows that, if a piece of it be placed in the same situation as the
ground glass, the reflected image, be it a landscape, a figure, or
an artificial object, will be formed on it. All that is, therefore,
required to be done, in using the camera obscura for photographic
drawing, is to place upon the opening at the top of the box the
prepared paper, and immediately to cover it with the lid, C, so that
it may not be acted upon by any other light than that reflected from
the mirror. The time required for producing the necessary effect will
depend on several circumstances, such as the preparation of the paper
and the intensity of the light when the experiment is made; the latter,
however, is by far the more important. On a bright sun-shining day,
the drawing will be produced in one-half the time, and with far more
sharpness of outline, than on a dull wintry day, when the sun struggles
with the mists by which its radiant beams are encumbered. “The Pencil
of Nature,” is the expressive title of a collection of photographic
drawings, produced by Mr. Talbot. Upon the third part of this work, we
find the following acute criticism in the _Athenæum_, No. 920.

“The subjects are ‘The Entrance Gateway of Queen’s College, Oxford;’
‘The Ladder,’ in which we have three figures from the life; and ‘A
View of the Author’s Residence, Lacock Abbey, in Wiltshire.’ In the
first of these, the truth-telling character of photographic pictures
is pleasingly shown. It appears, by the turret clock, that the view
was taken a little after two, when the sun was shining obliquely upon
the building. The story of every stone is told, and the crumbling of
its surface under the action of atmospheric influences is distinctly
marked. The figures in ‘The Ladder’ are prettily arranged, but the face
of the boy is distorted, from the circumstance of its being so very
near the edge of the field of view embraced by the lens of the camera
obscura. In looking at this photograph, we are led at once to reflect
on the truth to nature observed by Rembrandt, in the disposition of
his lights and shadows. We have no violent contrasts; even the highest
lights and the deepest shadows seem to melt into each other, and the
middle tints are but the harmonizing gradations. Without the aid of
colour, with simple brown and white, so charming a result is produced,
that, looking at the picture from a little distance, we are almost
led to fancy that the introduction of colour would add nothing to its
charm.”

The following is the patent process for obtaining a negative
picture:--Take a sheet of paper, with a smooth surface, and a close
and even texture, and without the water-mark, and wash one side of
it, by means of a soft camel’s-hair brush, with a solution composed of
one hundred grains of crystallized nitrate of silver dissolved in six
ounces of distilled water, having previously marked with a cross the
side which is to be washed. When the paper has been dried cautiously at
the fire, or spontaneously in the dark, immerse it for a few minutes
(two minutes, at a temperature of sixty-five degrees,) in a solution
of iodide of potassium, consisting of five hundred grains to one pint
of distilled water. The paper is then to be dipped in water, and
then dried, by applying blotting-paper to it lightly, and afterwards
exposing it to the heat of a fire, or allowing it to dry spontaneously.
The paper thus prepared is called iodized paper, and may be kept for
any length of time in a portfolio not exposed to light. When a sheet of
paper is required for use, wash it with the following solution, which
we shall call No. 1; take one hundred grains of nitrate of silver,
dissolved in two ounces of distilled water, and add to this one-third
of its volume of strong acetic acid. Make another solution, No. 2, by
dissolving crystallized gallic acid in cold distilled water, and then
mix the two solutions together in equal proportions, and in no greater
quantity than is required for immediate use, as it will not keep long
without spoiling. This mixture, called gallo-nitrate of silver, by the
patentee, is then to be spread, by a soft camel’s-hair brush, on the
marked side of the iodized paper; and, after allowing the paper to
remain half-a-minute to absorb the solution, it should be dipped in
distilled water and dried lightly; first with blotting-paper, and then
by holding the paper at a considerable distance from the fire. When
dry, the paper is ready, and it is advisable to use it within a few
hours.

The paper, which is highly sensitive to light, must now be placed
in the camera obscura, in order to receive on its marked surface a
distinct image of the landscape or person whose picture is required.
After remaining in the camera from ten seconds to several minutes,
according to the intensity of the light, it is taken out of the
camera in a dark room. If the object has been strongly illuminated,
or if the paper has been long in the camera, a sensible picture will
be seen on the paper; but, if the time of exposure has been short,
or the illumination feeble, the paper will “appear entirely blank.”
An invisible image, however, is impressed on the paper, and may
be rendered apparent by the following process:--Take some of the
gallo-nitrate of silver, and, with a soft camel’s-hair brush, wash the
paper all over with this liquid, then hold it before a gentle fire,
and, in a short time, the image will begin to appear; and those parts
upon which the light has acted most strongly will become brown or
black, while the others remain white. The image continues to grow more
and more distinct for some time, and, when it becomes sufficiently so,
the operation must be terminated, and the picture fixed. In order to
effect this, the paper must be dipped first into water, then partly
dried by blotting-paper, and afterwards washed with a solution of
bromide of potassium, consisting of one hundred grains of the salt,
dissolved in eight or ten ounces of water. The picture is then finally
washed in water and dried as before. In place of bromide of potassium,
a strong solution of common salt may be used.

By this process we get a negative picture--having the lights dark
and the shades light--and from it positive pictures may be obtained
as follows:--Dip a sheet of good paper in a solution of common salt,
consisting of one part of a saturated solution, to eight parts of
water, and dry it first with blotting-paper, and then spontaneously.
Mark one of its sides, and wash that side with a solution of nitrate
of silver, which we shall call No. 3, consisting of eighty grains of
salt, to one ounce of distilled water. When this paper is dry, place it
with its marked side uppermost on a flat board or surface of any kind,
and above it put the negative picture, which should be pressed against
the nitrated or positive paper by means of a glass plate and screws.
In the course of ten or fifteen minutes of a bright sunshine, or of
several hours of common daylight, a fine positive picture will be found
on the paper beneath the negative picture. When this picture has been
well washed or soaked in water, it is washed over with the solution
of bromide of potassium, already mentioned, or plunged in a strong
solution of common salt.[F]

A singular result of the application of this invention occurred to an
accomplished traveller, who ascended Mount Etna, in order to obtain
representations of that remarkable volcano. No sooner was the camera
fixed on the edge of the crater, and the sensitive paper introduced,
than a partial irruption took place, and the traveller had to fly for
his life. On the cessation of the irruption, he returned; doubtless,
with the expectation of merely collecting the fragments of his valuable
instrument; when, to his great astonishment and delight, he discovered
not only that his camera was absolutely uninjured, but that it
contained an admirable representation of the crater and the irruption.

A brief account of the process of the Daguerreotype may now be given. A
plate of silvered copper, about as thick as a shilling, is well cleaned
and polished by rubbing it with cotton, fine pumice powder, and dilute
nitric acid, and afterwards exposed to the heat of a spirit-lamp,
placed below it, till a strong white coating is formed on the polished
surface. On the plate being cooled suddenly by means of a cold slab of
stone or of metal, the white coating is removed by repeatedly polishing
it with dry pumice and cotton, and then three times more with the
dilute nitric acid and pumice powder.

A careful cleaning being thus given to the plate, it is placed in a box
containing iodine, till it becomes visibly covered with a golden film
of that substance, which must neither be pale nor purple. It is then
placed in the camera till a distinct picture of whatever appears before
it is formed upon the surface; it remains there for a period depending
on the intensity of the light, and is then removed to a metallic box,
having in it a cup containing at least three ounces of mercury. Placed
below the cup is a spirit-lamp, which throws off the mercurial vapour;
and, in exact proportion as this vapour deposits itself on the parts
of the plate which have been acted upon by the light, is the picture
developed on the surface of the plate, by the adhesion of the white
mercurial vapour to the different parts which had been impressed by
the light. As soon as the picture appears complete, the plate is
placed in a trough of sheet-copper, containing either a saturated
solution of common salt, or a weak solution of hyposulphite of soda.
Thus, the coating of iodine will be dissolved, the yellow colour quite
disappearing; hot, but not boiling, distilled water is then poured over
the plate, and any drops which remain are removed by blowing upon them.

The picture being now finished, is preserved from dust by placing it
in a frame, and covering it with glass. In every successful operation,
the picture is almost as perfect in its details as that of the camera
obscura itself; but, as the light of the sun is only white, there can
be, of course, none of the varied tints of nature. The shades are
supplied by the black polish of the metallic surface which, when it
reflects a luminous object, the white vapour of the mercury appears
in shade, and thus gives us either a positive or a negative picture,
according to the light in which it is viewed.

Various improvements have gradually been made in the processes of the
Daguerreotype and the Talbotype, which our limited space forbids us to
describe. Mr. Beard has added colour to his Daguerreotype portraits,
which is uniform and so transparent as not to affect the likeness
in any degree, while the life-like effect is greatly heightened. M.
Claudet has found that, when the sun is rendered red by the vapours of
the atmosphere, it not only produces no effect upon the Daguerreotype
plate, but that it destroys the effect previously produced by the
white light. If the image of the red sun be taken in the camera
obscura, it produces upon the Daguerreotype plate a black image. By
covering a Daguerreotype plate previously affected by light with a
red, orange, or yellow glass, the radiation through these coloured
media has also the property of destroying the action produced by white
light. The most interesting part of M. Claudet’s statement refers to
the fact that, after the destroying action of the red, orange, and
yellow radiations, the plate is restored to its former sensitiveness;
so that, after having been affected by white light, and restored by
the destructive action of the red, orange, and yellow radiations, it
is possible to produce a photographic effect, as upon a plate just
prepared with iodine and bromine. This alternate acting and destroying
action may be repeated _ad infinitum_, without altering the final
state of the plate. This curious fact proves, evidently, that, in the
Daguerreotype process, light does not alter the chemical compound on
the plate, and that the affinity for mercury is the result of some new
property imparted by the action of the rays of light. M. Claudet’s
experiments prove, also, that the red and yellow rays are endowed
with a photographic action of their own, which, as well as that of
the blue and violet rays, gives an affinity for mercurial vapour. The
photographic action of the red ray is destroyed by the yellow, that
of the yellow by the red; the red and yellow destroy the photographic
action of the blue, and the blue destroys the action of the others.
The photographic, or the destroying action of any particular ray
cannot be continued by any other. It appears, therefore, that each
radiation changes the state of the plate, and each change produces the
sensitiveness to mercurial vapour when it does not exist, and destroys
this sensitiveness when it does exist.[G]