Photography

3722

Phrenology

and is carried on until an image of sufficient
density is obtained. The image is then fixed
by immersing it in a solution of sodium hy-
posulphite. Prints are then obtained from
the negative by placing it in front of a piece
of sensitized paper and exposing to light. The
light passes through the negative most read-
ily in the clearer portions, thus darkening the
paper most at the places where little light
fell on the plate when in the camera, and
hence reproducing the shadows of the object.
Similarly the high lights of the object pro-
duce opacity in the negative, and this gives
light places on the print.

Within the last few years by the discovery
of a new class of dyes, the so-called 'isocyan-
ines,' the sensitiveness of the silver salts for
the red end of the spectrum has been so much
increased that the 'panchromatic' plate, sen-
sitive to all colors, has placed an absolutely
new power in the hands of the photographer
both for artistic and scientific work. If suit-
able filters, that is, scientifically adjusted
films of gelatin stained with aniline dyes, are
inserted between the lens and the sensitive
surface, it is possible to obtain a perfectly
true representation of the relative brightness
of different colors. This discovery may be
practically said to have been one of the big-
gest advances since the discovery of photo-
graphy. Photography has become the hand-
maid of science and commerce. In legal cases
photographs of objects and places are fre-
quently introduced into court for the pur-
pose of aiding the jurors to a more intelligent
understanding of the facts of a case. In as-
tronomy, photographs of the heavens are
furnishing extremely valuable data for re-
search and investigation; while in biology
and zoology the art is invaluable in the study
of the life, haunts, and habits of wild ani-
mals, reptiles, and insects. Photographs of
micro-organisms have been exceedingly use-
ful in medicine, and photographic exhibits
play an important part in campaigns for the
promotion of health and the prevention of
disease. Photography as an adjunct to adver-
tising is of constantly growing importance;
while the large number of illustrated cata-
logues issued periodically bear witness to its
r61e in the business of selling. With the in-
creasing demand for photographs for pub-
licity purposes, a considerable number of
companies have been incorporated for the
sole purpose of securing and supplying pho-
tographs of prominent persons, places, and
objects, for publishing and advertising

houses. The possibilities of the field of tele-
vision have by no means been explored, but
it is along these lines that many photographic
experiments are now being made. The ap-
plication of photography in military prac-
tice is of special interest. In all wars previ-
ous to World War I photography had been
largely in the hands of civilians, doing their
work for profit and in haphazard manner.
While there were a few authorized photogra-
phers in the Signal Corps, there was no sepa-
rate corps of photographers in the U. S. Army
until its entrance into the European War in
1917. Present-day military photography falls
into two grand divisions: photography in the
air, and photography on the ground. Of these
the most important is aerial photography. An
important function of the Aviation Services
of all armies is carrying military photogra-
phers over the lines so that they may make
record photographs revealing enemy works.
By 1918 an automatic camera had been
evolved that, once its mechanism was set
tfoing, did not need further attention from
the operator. In World War II photography
in its many phases played a very important
role. Consult Journal of the Photographic
Society of America; C. E. K. Mces, The
Theory of the Photographic. Process. See
MOVING PICTUKKS.

Photometry is the measurement of the
relative amounts of light emitted by different
sources, by comparing them with a suitable
standard. The ordinary unit of measurement
used in the United States and Great Britain
is the candle-power, which is the light pro-
duced by a standard candle of weight six to
the pound, burning 120 grains of spermaceti
wax per hour. There are many different kinds
of photometers. Among the simplest are the
Rumford and the Bunsen, Consult Fleming's
Handbook for the Electrical Laboratory;
Palaz's Industrial Photometry (Eng. trans,);
Stine's Photometrical Measurements; Record
of the International Congress of Physicists,
1900.

Photophone, an instrument invented by
Graham Bell and Sumner Tainter, by which
sounds, including speech, can be transmitted
to a distance by the agency of light.

Photosphere, the sun's radiating surface,
probably composed of incandescent clouds
floating in a less luminous medium.

Phrenology, a pseudo-science, whose de-
votees claim that the external features of
the skull furnish an index to the mind and
character. Franz Joseph Gall, a German,