Crawford avalanche. (Grayling, Mich.) 1879-19??, 1899-05-18
THE BIOGRAPHS SECRETS.
now OBJECTS IN MOTION ARE REPRO
DUcED WITH STARTLING REALISM.
Films $50 Yards In Leagth--.yeu Don't See
One Moving Picture, a. You Think, but
Hundreds Of Stationary Photographs. Fol.
lowing Each Other RapIdIy.

Hundreds Of Stationary Photographs, Fol-
lowing Each Other Rapidly.
The fundamental principle upon
which a moving picture apparatus Is
constructed is the principle OF the re-
tention Of the image by the retina OF
the eye. 1t is well known that the du-
ration of fash of lightning Is an ex,
ceedingly small fraction of a second.
Nevertheless, this brief period OF illu-
mination is sufficient to imprint upon
the retina perfect picture OF
landscape; and the impression Of the
beholder Is that the period Of illumi-
nation Is enormously greater than 1t
actually is. Working on this principle,
a series of photographs are taken on a
long strip Of celluloid film. The time
of exposure Of these pictures is ordi-
narily very much shorter than Is en-
plOyed In so-called instantaneous pho
tographs taken by hand cameras, the
period Of exposure ranging from l.
Tooth to 1-4O0th part of second. After
each exposure, which Is ordinarily
made by n revolving shutter, having a
slit or opening through which the light
Is permitted to reach the sensitized
film for a brief instant, the film is
moved forward by the mechanism of
the camera until new surface comes
opposite the lens. The film is then
usually held stationary while a second
exposure Is made. This process is re-
peated in n biograph camera at the
rate Of about thirty exposures per Sec
Ond, and ii will thus be noted that the
time of the moving film occupies a
much greater proportion of the time
than is used in making the exposure.
The actual time of exposure depends
upon number of conditions.
One of these is the rapidity of move
ment Of the object being photo
graphed; thus fast moving objects like
an express train will permit of only
very short eXposure-perhaps 1-3OOth
part of a second-in order that the
picture may be sharp and distinct; for
if the object moves an appreciable dis
lance during the time the exposure is
being made the picture that results is
blurred. Comparatively slow moving
objects, such as parade or a vessel
admit of a longer exposure.
The light conditions during the time
the picture is being taken must also
be considered. Therefore, in order to
gee sharp picture of rapidly moving
object it is necessary to have brilliant
sunshine, while pictures of slower
moving objects may be taken in sat.
isfactory manner when the light con-
fa
After series of negatives have been
obtained. the long strip of film, 2A
inches wide and ranging from $50 to
$50 or more feet in length, is taken in
TO the dark room and wound upon
large wire drum. This drum is then
rotated in vat of developing solution,
and the whole series of one thousand
or more negatives are developed in
about the same time that is ordinarily
required to develop single photo
graphic negative.
After the strip is developed and
dried. ii is run through an automatic
printing machine together with strip
of positive film of the same width and
length. This printing machine is a
very intricate automatic device, and
by it perfect positive reproduction of
the entire negative is made in short
space of time; special pains being
taken that the pictures shall register
perfectly one after another, so that
when reproduced by the biograph,
there may be no vibration between
successive pictures. This positive
print is developed in manner similar
to the negative and after being thor
oughly dried. is ready for use.
AS many of these positives as it Is
desired to exhibit are spliced together
and wound upon large reel or drum;
thus forming one continuous band of
film many thousand feet in length.
The film is led from this receiving reel
over series Of pulleys and through
a number of clamps and down into a
winding-up reel; the operation of the
machine being such that when
the pictures comes opposite the
projecting lens of the machine
through which the light from
powerful arc light is directed the film
stands stationary, allowing the picture
to rest quietly upon the screen. A
shutter then revolves, cutting off the
light from the picture, and during this
brief interval of darkness the film is
moved forward exactly the space of
one picture. allowing the following
pictures to take their place upon the
screen one after the other, each sue
ceeding picture being separated from
the preceding one by the same brief
interval of time that elapses when
the pictures were taken. The result
is that through optical illusion the eye
eye does not detect the change of pie
ture and apparently only sees one pic
ture, but the objects in this picture
appear to move as in life.
If the number of pictures presented
to the eye is too small, disagreeable
flicker, very trying to the eyes, is no.
ticed, and If the succeeding pictures
that pass before the lens Of the ma
chine do not register perfectly one
after the other then even the station
airy figures in the picture appear to VI
brate and dance about in the most OBJ
jectionable manner.
An electric motor runs the machine
with q uniform motion, adapted to
present the pictures to the eye at ex-
actly the same speed with which they
We're taken. This is n most essential