ough if one
negative was compared to its neighbour scarcely any variance would be
noted.

After the film has been exposed, the light-tight box containing it is
taken out of the camera and taken to a gigantic dark-room, where it is
wound on a great reel and developed, just as the image on a kodak film
is brought out. The reel is hung by its axle over a great trough
containing gallons of developer, so that the film wound upon it is
submerged; and as the reel is revolved all of the sensitised surface is
exposed to the action of the chemicals and gradually the latent pictures
are developed. After the development has gone far enough, the reel,
still carrying the film, is dipped in clean water and washed, and then a
dip in a similar bath of clearing-and-fixing solution makes the
negatives permanent--followed by a final washing in clean water. It is
simply developing on a grand scale, thousands of separate pictures on
hundreds of feet of film being developed at once.

A negative, however, is of no use unless a positive or print of some
kind is made from it. If shown through a stereopticon, for instance, a
negative would make all the shadows on the screen appear lights, and
vice versa. A positive, therefore, is made by running a fresh film, with
the negative, through a machine very much like the moving-picture
camera. The unexposed surface is behind that of the negative, and at the
proper intervals the shutter is opened and the admitted light prints the
image of the negative on the unexposed film, just as a lantern slide is
made, in fact, or a print on sensitised paper. The positives are made by
this machine at the rate of a score or so in a second. Of course, the
positive is developed in the same manner as the negative.

Therefore, in order to show the people in the theatre the Suburban, five
hundred feet of film was exposed, developed, fixed, and dried, and
nearly ten thousand separate and complete pictures were produced, in the
space of two hours and fifteen minutes, including the time occupied in
taking the films to and from the track, factory, and theatre.

Originally, successive pictures of moving objects were taken for
scientific purposes. A French scientist who was studying aerial
navigation set up a number of cameras and took successive pictures of a
bird's flight. Doctor Muybridge, of Philadelphia, photographed trotting
horses with a camera of his own invention that made exposures in rapid
succession, in order to