Evening star. [volume] (Washington, D.C.) 1854-1972, 1890-11-15

l
over the world are engaged upon the subject
and already they have arrived at partially sue.
cessful results. There is one Frenchman who
claims that he has actually discovered a sue.
cessful process though others dispute his as
sertion.
You must understand that photosraphing
In colorsi is. in one sense. no new thing. As early
as the days of the uaguerreotype it was some
times accomplished by accident. That is 10
say, once In while the sun picture would be
found TO have reproduced ~ color IN some
mysterious way that no one knew how to ex-
pam. 1t has since been surmised that the
curious result was due to a trace OF copper that
got into the sensitive surface. At All events
copper has been employed IN efforts to get
colors since and with some degree of success.
However. it has been found much better for
the purpose to use chloride OF silver. which is
made, by exposure 20 light for a certain time.
sensitive to color waves. But the trouble has
been with experiments in this line that the
colors would not remain. They can be pro-
Iueed usually now, but how TO fix them is the
ulinculty. so that they will stay. Nevertheless,
longer l expect and portraits and other pictures
Will be painted in colors by the camera.
RETAINING COLOR VALUES.
"A great Improvement has recently been in
troduced in the shape of 'isochromatic' plates,
made with new chemical composition, which,
though they do not reproduce the colors
actually, DO give, in a way that they have never
hitherto been given, the values of the colors
OF objects. To explain what / mean, look at
III, anose two photographs of vase full of flowers,
The vase was in light yellow and the bouquet
was made up OF yellow jonquils, blue hya-
clnths and white narcissus. One of the photo
graphs Is from an ordinary plate. and you will
observe that all the color values are lost The
narclssus comes out white. because it is white;
ha Ill
son that yellow takes that way; the jonquils
are nearly black also, aud the hyacinths look
anything but blue. Now, on the other hand,
look at this other photograph, which is of the
Same vase and posy from an 'isochromatic
plate. You see that in the latter, though no
by the shading that the hyacinths really look
blue and the ionquils and the vase light vel.
low, as in the original. This you cannot help
admitting is In itself great step ahead.
COLOR PHoTo-NIcRoGRArHs.
"Color photography would be great help to
us in our work Of making acknowledgements of
sections of rocks. In the so-called 'lithologi-
cal division of the National Museum we try to
exhibit the various rocks of the world in four
ways. We show. first. block of a particular
kind OF stone Next. We give in figures the sup
porting strength OF that stone. Third. we offer
a picture in water colers, showing how a build
ing made Of that stone will look. And finally
We hang up on the window, where the light
shines through it, greatly magnified section
of the stone as il is seen under a microscope by
polarlzed light For this last purpose a small
piece of rock Is ground down until 1t is the
thinness possible transparent film. raw of
light is passed through prism of Iceland spar,
which has the peculiar property of SO separat-
ing the light waves as to 'polariZe' the light
as the technical phrase is. Precisely the
meaning of this 1t would take too long to ex-
plain in detail, but it is sufficient to
say that it has certain effect of
refraction which accomplishes the purpose /
wish to describe. The ray of light. having
gone through the prism of Iceland SPAR passes
on through the film of rock. which is mounted
on glass plate, and beyond through micro
scope, the Other end of which is fitted into a
camera. Thus a very much magnited image of
the rock section is thrown upon the sensitive
plate inside the camera and big picture of il is
made. The picture is merely in black and
white, but the image produced ON the ground
glass at the back of the camera is in all sorts
OF beautiful colors each element of which the
stone is composed being made by the refract-
ing effect OF the polarlZed light to take on a
tint of Its own, so that the least pretty bit of
ordinary cobblestone is patchwork Of lovely
hues. As ii is We are obliged to tint the photo
graphs with water colors, copied after the
image on the ground glass; but. if we had a
way to photograph colors, the exquisitely
tinted pictures of the stones could be obtained
directly. II you care to look at the windows in
the south wing of the museum, which light the
Theological exhibition you will see a number
of these colored photo-m icrographs just as
they would appear to your eye if you looked at
the originals through microscope. They are
put up on the windows in order that the light
may shine through them and show their trans
parency. exactly would be the case if you
were employing a microscope for tho examine
tiOn of he sectOns