surface. In
connection with this problem it is interesting to note that this
question of high speed was apparently regarded by all Edison's
predecessors as the crucial point. Ducos, for example, expended a great
deal of useless ingenuity in devising a camera by means of which a
tape-line film could receive the photographs while being in continuous
movement, necessitating the use of a series of moving lenses. Another
experimenter, Dumont, made use of a single large plate and a great
number of lenses which were successively exposed. Muybridge, as we have
seen, used a series of cameras, one for each plate. Marey was limited to
a very few photographs, because the entire surface had to be stopped and
started in connection with each exposure.

After the accomplishment of the fact, it would seem to be the obvious
thing to use a single lens and move the sensitized film with respect to
it, intermittently bringing the surface to rest, then exposing it, then
cutting off the light and moving the surface to a fresh position; but
who, other than Edison, would assume that such a device could be made
to repeat these movements over and over again at the rate of twenty to
forty per second? Users of kodaks and other forms of film cameras will
appreciate perhaps better than others the difficulties of the problem,
because in their work, after an exposure, they have to advance the
film forward painfully to the extent of the next picture before another
exposure can take place, these operations permitting of speeds of but
a few pictures per minute at best. Edison's solution of the problem
involved the production of a kodak in which from twenty to forty
pictures should be taken IN EACH SECOND, and with such fineness of
adjustment that each should exactly coincide with its predecessors even
when subjected to the test of enlargement by projection. This, however,
was finally accomplished, and in the summer of 1889 the first modern
motion-picture camera was made. More than this, the mechanism for
operating the film was so constructed that the movement of the film took
place in one-tenth of the time required for the exposure, giving the
film an opportunity to come to rest prior to the opening of the shutter.
From that day to this the Edison camera has been the accepted standard
for securing pictures of objects in motion, and such changes as have
been made in it have been purely in the nature of detail mechanical
refinements.

The earliest form of