ld
be one-tenth of a second; and for a normal eye such an exhibition would
present a substantially continuous photograph. If the angular movement
of the object across the field is very slow, as, for instance, a distant
vessel, the successive positions of the object are so nearly coincident
that when reproduced before the eye an impression of smooth, continuous
movement is secured. If, however, the object is moving rapidly across
the field of view, one picture will be separated from its successor to a
marked extent, and the resulting impression will be jerky and unnatural.
Recognizing this fact, Edison always sought for a very high speed, so as
to give smooth and natural reproductions, and even with his experimental
apparatus obtained upward of forty-eight pictures per second, whereas,
in practice, at the present time, the accepted rate varies between
twenty and thirty per second. In the efforts of the present day
to economize space by using a minimum length of film, pictures are
frequently taken at too slow a rate, and the reproductions are therefore
often objectionable, by reason of more or less jerkiness.

During the experimental period and up to the early part of 1889, the
kodak film was being slowly developed by the Eastman Kodak Company.
Edison perceived in this product the solution of the problem on which he
had been working, because the film presented a very light body of tough
material on which relatively large photographs could be taken at rapid
intervals. The surface, however, was not at first sufficiently sensitive
to admit of sharply defined pictures being secured at the necessarily
high rates. It seemed apparent, therefore, that in order to obtain
the desired speed there would have to be sacrificed that fineness
of emulsion necessary for the securing of sharp pictures. But as was
subsequently seen, this sacrifice was in time rendered unnecessary. Much
credit is due the Eastman experts--stimulated and encouraged by Edison,
but independently of him--for the production at last of a highly
sensitized, fine-grained emulsion presenting the highly sensitized
surface that Edison sought.

Having at last obtained apparently the proper material upon which to
secure the photographs, the problem then remained to devise an apparatus
by means of which from twenty to forty pictures per second could be
taken; the film being stationary during the exposure and, upon the
closing of the shutter, being moved to present a fresh