Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1892-02-07
CATCHING SUNBEAMS.
The Science of Photography on the
Verge of Great Development.
SOON TO HAVE COLOR PICTURES.
Conquests Of the Sky and Its Alliance
With the Printing Press.
THE UTILITY OF FUGITIVE DYES
lwR1rrEy FOR THE pIspATcH.I


may suggest q new use for which the thing,
actly fit; and the new use may be much
more important than the old one. When
dyes from coal tar, oils, and Peruvian bark
were first made they had provoking way
of fading out of their fabrics in few days,
or even in few hours. Usually, too, the
more brilliant the tints the more fugitive
they were. That defect has, in large meas
ure, been overcome, but before it yielded to
the resources of the laboratory remarkable
series of experiments took place.
1t was in 1873 that DR.. H. W. Vogel, of
Berlin, observed that certain Photographic
plates of his had much more than ordinary
sensitiveness to rays of green light. Search
ing for the reason he noticed that the plates
were of somewhat reddish color Could it
be possible that tine mere accident of color
had conferred a new quality of sensitive
ness upon the films? He determined to
put the question to the test of experiment
forthwith, and at once procured some chino
line and pyrodine dyes-red, violet and blue
beautiful in tint, but feeting and worth
less. As he looked on these fine colors his
reflections did not take the direction of seek
ing some method of making them enduring.
Bad In One Way Good in Another.
Thought he, this eyanscence is certainly
very bad when we wish to give color to q
cloth, but, after all, it only means extreme
sensitiveness to light, and that may be q
very valuable popularity. Indeed, it is
just such property which gives the COM
pounds of silver their importance in photo
graphy. And noteworthy point about
these dyes is that they are impossible by
the red and yellow rays which scarcely
affect the silver salts at all. Perhaps If
they were applied to Photographic plate
they would make it sensitive in new and
most useful way.
Acting on those ideas, DR.. Vogel began Q
course of experiments which issued in his
giving photography a fidelity to nature
which it had never before enjoyed. To his
delight he found that many fugitive dyes
entered into chemical combinations with
the salts of silver, comforting upon his films
their own peculiar susceptibility to certain
rays of light. Anybody who has ever de-
veloped an ordinary Photographic negative
knows that the only light safe to employ
for the purpose is what little Sits its way
through panes of red or canary glass, be-
cause red or yellow rays have no influence
whatever on the plates silver coating.
Hence arises serious want of truth in the
picture; red rose or a red gown comes out
as if black, and SO does q yellow aster or
mass of yellow foliage.
Photos Of Many Colored Flowers.
With the orthochromstic plates that We
owe to DR.. Vogel and the chemists who
have followed his lead, that falsity in color
values ceases. 1t is accomplished by their
bringing visual intensity and Photographic
intensity to harmony. A plate tinged with
cyanin, beautiful blue substance, has sur
passing sensitiveness to orange rays; stained
with erythrosin, preparation red in color,
it takes on in addition a high impressibility
to yellow light. Armed with such plate
photographer, with close approach to truth
of effect, can take picture of q varigated
flower bed, of autumn woods, of lady in
richly colored costume. Despite the plates
Improvement blue and violet rays may con-
tinue to impress it in an undue degree.
To remedy that screen of glass or film of
gelatine, stained yellow, cut off the over
active rays during part of the exposure;then
for moment the screen or film is with
drawn and the blue and violet rays are per-
mitted to imprint themselves.
To the dyes for which We are indebted to
Dr.. Vogel many additions have been made
year by year. The garden as we'll as the
laboratory has been laid under contribu-
tion, chiefly for chlorophyll, the green col
oring matter of leaves. Solutions of it de-
rived from the plantain, blue myrtle and
many other plants have been added to the
Photographic film with results always inter-
esting, if only rarely Of practical value.
Taking Pictures by Gaslight.
Orthochromy has shared in the impetus
received BY every branch of photography
since the introduction Of bromide-gelatine
plates, and were orthochromatic plates as
quickly impressed and as easily developed
as common plates their use would be much
more general Because they are acted upon
by the red and yellow rays of gaslight and
oillight they can be employed at night, and
although the exposure must be longer than
by daylight it is by no means tedious
Orthochromatic plates have especial value
in the reproduction of oil paintings, which
they render into monochrome with a per-
fection unimaginable in the days before
silver of salts and dyes were brought
together.
Beyond every other achievement of the
camera must rank the marvels it reveals
when directed to the orbs of heaven, and in
this noble field of work the new plates en-
large the instruments powers in very won-
derful way. Every chemical element, when
it reaches glowing heat, gives out light OF
characteristic color. When we have once
seen the yellow fame of sodium, or the red
beams shot forth by strontium, we can al
ways detect the presence of these substances
in a pyrotechnic display. 1t is by an ex-
tension of this principle that the story of
the spectroscope is spelled out The pio-
neer in this remarkable field of research
was DR.. Henry Draper, of New York, who
first secured q well-defined star spectrum in
the camera Since his death in 1882, and
through the liberal endowment of Mrs.
Draper, his work has been continued by
Prof. E. G. Pickering of the Harvard OBJ
seryatory.
A New Means OF Exploration.
Photographs of stellar spectra are now
taken in Peru as well as at Cambridge, and
by staining the plates with erythrosin the
include thosesot the green and
yellow rays which exert no action on an or
dinary film. Varied as these experiments
are, they are far from exhausting the pos
of the camera Beyond the violet
rays of the spectrum's rainbow extend vi
brations which, though invisible to the eye,
have since the very early days of photog-
raphy been caugh. and detained on its
plates At the other end of the spectrum,
beyond the red, are other invisible radia-
tions, detected easily by a delicate ther-
which until 1887 eluded capture.
In that year. Captain Abney secured an
image from them on . bromide of silver
plate.
He maintains that here, and in the use of
plates sensitive to ultraviolet rays, astron-
omers have new means of exploration,
with which they are free to enter upon
fresh chain of discoveries To the stars
already known it is within their power to
add new class-stars newly born or newly |