Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1892-07-06
PERFECT PHOTOGRAPHY.

Lippmann's Discovery as to Colors Com
pletes the Art-A French Writer'S Opin-
ions on tho Advancement Made by His
Countrymen.
Alphonse Berget has written an article
on Lippmann's great discovery wh1cn
eratuve In it he says that the
remarkable thing about DR.. Lipp.
mann's discovery is, fret OF all. the result
obtained which : fills the gap which re-
| mafned to be filed in the art OF photog-
raphy. Indeed, he has given his attention
| to scientific principle Of the utmost n1cety
in arriving at the end he had in view. Let
| me attempt in few words to give the es-
sence of this discovery. His method is
simplicity itself Take a plate with any
kind of a sensitized film. This flm need
only be transparent and free from granula-
| tions and fmperfectfons. Expose 1t as usual
in the camera obscura, turning the sensi-
tized side of the plate away from the lens,
but taking care to place against this plate q
| mirror Of perfect polish.
This mirror is made of a thin coating of
| mercury hold between the sensitized glass
and another glass at the back Of It. Then
follows the fuse as usual, the negative is
fixed, and when dry. 1t shows, without any
manipulation, the colors Of the object pho
| tographed. They are in this state durable
| and permanently fixed. Neither pigment
nor coloring matter of any kind has been
| used. Furthermore, the sensitized film re-
mains transparent as before, and is not in
itself colored. The reproduction of the
color is therefore not artificial, but is due to
natural phenomenon, of which l will try
to explain the mechanism. The expert
ments of physicists have made it possible to
explain with precision the nature of light.
1t is the result Of a vibratory motion, like
sound; and, like sound, is propagated by
waves.
Similarity OF Light and Sound.
While sound only travels at the rate of
$50 metres a second, light In the same time
traverses 800 600 kilometres. And while
sonorous bodies, such as the strinSs Of vio-
lins only make few hundred vibrations,
the molecules Of the ether which transmit
light execute trillions. Light is therefore
like sound, but It Is measured by greater
numbers. lift is thus with sound and light,
how about colors? The answer is simple.
Colors are but notes in the light scale, the
successive steps in the ladder of sound; and
just as two chords of different vibrations
give different sounds, so colors are differ
en- tiated by the number of pulsations of the
ether. For this reason the rain bow has been
IS he result OF an nsT
of colors succeeding each other by grada-
tions from red to purple on the prismatic
scale. This is shown when ray OF light
enters prism perfectly white and emerges
broken up into all the elementary colors of
the rainbow. We know, therefore, that
color comes of vibratory motion.
What, then, would be the result If two
such motions were to meet? Precisely the
same thing happens when two runners meet.
If they are going in the same direction, their
energies can be Joined to pull burden; but
nnnnQitA dirpcti0Do
simply stop each others progress. So with
waves of sound and light. Thus we see that
it is possible for one sound added to another
to produce silence; and one light added to
another surprising as it seems. may make
darkness. Now let us see what happens
when light is reflected in a mirror. The
direct light will meet in its journey the light
which has been thrown back just before its
arrival; so that whenever the two motions
are in the same direction the inters rsity will
be doubled, but when they oppose each
The space, therefore, in front OF a mirror
will be divided into cheeks (tranches) or
& ssrascations In some Of
others there will be no light at all. Let me
hasten to say that, the size of these cheeks
being only the one-four-millionth part of a
millimetre, they are not observable to the
eye. but show simply a uniformly lighted
surface.
The Reproduction of Colors.
But where the eye fails the Photographic
plate does not; and if the front of the mirror
is curved with a film sensitive to light, the
stratifications mentioned are reproduced in
this sensitive film. 1t follows that the lu-
minous impression will be made only
in the cheeks where the light is
at its maximum, whereas there will |
be no action where the film is obscure. II |
you develop such a plate, it's thickness will
be filled with a series of layers of photo |
graphic film, one separated from the other
differ from one another according to the !
color which has 1mpinged the plate at the |
point in question. What is the use of these |
layers of silver deposited under the chemi- |
cal action of light? This only remains to be |
told. These layers are the organ for the re- |
production of colors, without need of being |
colored themselves. Let me explain. Every |
time that transparent body is placed |
under q very thin lamella or plate, it appears
with irridescent coloring, though made
of colorless substance. Soap bubbles
the fact that the light reflected on the two !
faces of the very thin plates QamelIae) has
not gone over the same course. Physicists
call this the phenomenon of interference
It is furthermore known that colors differ
according to tine thickness of the lamella.
Thus, when soap bubble first appears at
the end of straw it first reflects violet
then blue. then green, then yellow. then red,
until it has grown SO attenuated that it
bursts. 1t is easy to see how important are
these silver layers in the body of the SEN
lamella of soap bubble, and sends TO tho
eye the color Of the light which gave it
birth.
The problem in photography is solved by
precisely similar causes. Such is q brief
sketch of this magnificent discovery, worthy
In every way of French science. Let me
add a few practical details to give general
idea of the question. Since it is these
which by reflection reproduce the
color, no obstacle of any kind must be per-
nitted to prevent them from lodging in the |
film. Therefore this film must
have no granulations to obstruct by their
relative enormous size the rejecting layer.
This excludes at once plates with bromide
Of silver such as are used in commerce, and
will not prevent the use of collodion, or,
more properly speaking, of albulnen sensi-
;ized in bath. This is good deal, of
course, to lose. To-day we are used to
Effects but In old times we
we're content to await results, and the re-
ults in this case are, in their beauty, well
worthy Of the trouble.